集合
我们接下来要学习的内容是Java基础中一个很重要的部分：集合
为了更好的理解集合，我们需要首先引入一个概念：泛型
1 泛型
1.1 概念
我们可以观察一下，下面的代码中有什么元素是我们之前没见过的呢?
其实就是< ? >的部分,它就是泛型
泛型是（Generics）JDK1.5 的一个新特性，通常用来和集合对象一起使用
泛型概念非常重要，它是程序的增强器，它是目前主流的开发方式
1.2 作用
那泛型有什么作用呢？
我们可以把泛型理解成一个“语法糖”，本质上就是编译器为了提供更好的可读性而提供的一种小手段，小技巧，虚拟机层面是不存在所谓“泛型”的概念的。是不有点神奇，不知所云，别着急等我讲完你就清楚了。
我们可以通过泛型的语法定义<>,来约束集合中元素的类型,编译器可以在编译期根据泛型约束提供一定的类型安全检查，这样可以避免程序运行时才暴露BUG,代码的通用性也会更强
泛型可以提升程序代码的可读性,但是它只是一个“语法糖”(编译后这样的部分会被删除,不出现在最终的源码中),所以不会影响JVM后续运行时的性能.
1.3 泛型示例
示例1 : 我们创建一个ArrayList,看到eclipse发出黄线警告,这是为什么呢?
原因:ArrayList定义时使用了泛型,在声明时需要指定具体的类型 
我们把这个”<>”的方式称之为泛型,那么泛型有什么样的作用呢?就是在编译阶段检查传入的参数是否正确
有了泛型,我们可以看到要求存放的是String类型,而测试时存放的是int类型的100,所以编译器报错:
类型List的add方法要求添加的类型为String类型,int类型不匹配,不能正确存入
1.4 泛型声明
泛型可以在接口 类 方法上使用
在方法的返回值前声明了一个,表示后面出现的E是泛型,而不是普通的java变量
1.5 常用名称
1.6 练习:泛型测试
创建包: cn.tedu. generic
创建类: TestGeneric1.java
package cn.tedu.generic;
import java.util.ArrayList;
import java.util.List;
/*本类用于测试泛型的优点/
public class TestGeneric1 {
public static void main(String[] args) {
/*1.泛型是怎么来的?–想要模拟数组的数据类型检查/
String[] a = new String[5];//创建一个用来存放String类型数据的数组,长度为5
a[2] = “泡泡”;
a[4] = “涛涛”;
//数组的好处:在编译时期检查数据的类型,如果不是要求的类型会在编译器就报错
//a[0] = 1;
//a[1] = 8.8;
//a[3] = ‘c’;
<span class="token comment">/**2.泛型通常会结合着集合一起使用*/</span>
List list <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//注意导包:java.util...</span>
<span class="token comment">//没有泛型,数据类型根本没有约束 -- 太自由!!!</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"江江"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">8.8</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">'a'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//通过打印查看集合中的元素</span>
<span class="token comment">/**3.引入泛型--主要目的是想通过泛型来约束集合中元素的类型<?>*/</span>
<span class="token comment">/**4.泛型的好处:可以把报错的时机提前,在编译期就报错,而不是运行后抛出异常
* 在向集合中添加元素时,会先检查元素的数据类型,不是要求的类型就编译失败
* */</span>
List<span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span> list2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//注意导包:java.util...</span>
list2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"雷神"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//约束了类型以后,只可以传String参数</span>
<span class="token comment">//list2.add(1);</span>
<span class="token comment">//list2.add(8.8);</span>
<span class="token comment">//list2.add('d');</span>
<span class="token comment">/**5.<type>--type的值应该如何写?
* 需要查看要存放的数据类型是什么,根据类型进行定义
* 但是type必须是引用类型,不是基本类型
*/</span>
<span class="token comment">//List<int> list3 = new ArrayList<int>();//注意导包:java.util...</span>
List<span class="token generics function"><span class="token punctuation"><</span>Integer<span class="token punctuation">></span></span> list3 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics function"><span class="token punctuation"><</span>Integer<span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//注意导包:java.util...</span>
list3<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list3<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list3<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
}
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1.7 练习:泛型测试2
创建包: cn.tedu. generic
创建类: TestGeneric2.java
package cn.tedu.generic; /**本类用来测试泛型的优点2*/ public class TestGeneric2 { public static void main(String[] args) { //需求:打印指定数组中的所有元素 Integer[] a = {1,2,3,4,5,6,7,8,9,10}; print(a);String<span class="token punctuation">[</span><span class="token punctuation">]</span> b <span class="token operator">=</span> <span class="token punctuation">{<!-- --></span><span class="token string">"大哥"</span><span class="token punctuation">,</span><span class="token string">"二哥"</span><span class="token punctuation">,</span><span class="token string">"三哥"</span><span class="token punctuation">,</span><span class="token string">"四哥"</span><span class="token punctuation">,</span><span class="token string">"五哥"</span><span class="token punctuation">,</span><span class="token string">"六哥"</span><span class="token punctuation">,</span><span class="token string">"小弟"</span><span class="token punctuation">}</span><span class="token punctuation">;</span> <span class="token function">print</span><span class="token punctuation">(</span>b<span class="token punctuation">)</span><span class="token punctuation">;</span> Double<span class="token punctuation">[</span><span class="token punctuation">]</span> c <span class="token operator">=</span> <span class="token punctuation">{<!-- --></span><span class="token number">6.0</span><span class="token punctuation">,</span><span class="token number">6.6</span><span class="token punctuation">,</span><span class="token number">6.66</span><span class="token punctuation">,</span><span class="token number">6.666</span><span class="token punctuation">,</span><span class="token number">6.6666</span><span class="token punctuation">}</span><span class="token punctuation">;</span> <span class="token function">print</span><span class="token punctuation">(</span>c<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token comment">/**1.泛型可以实现通用代码的编写,使用E表示元素的类型是Element类型 -- 可以理解成神似多态*/</span> <span class="token comment">/**2.泛型的语法要求:如果在方法上使用泛型,必须两处同时出现,一个是传入参数的类型,一个是返回值前的泛型类型,表示这是一个泛型*/</span> <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token generics function"><span class="token punctuation"><</span>E<span class="token punctuation">></span></span> <span class="token keyword">void</span> <span class="token function">print</span><span class="token punctuation">(</span>E<span class="token punctuation">[</span><span class="token punctuation">]</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span> <span class="token keyword">for</span><span class="token punctuation">(</span>E d <span class="token operator">:</span>e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span> System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>d<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span>
// public static void print(Double[] c) {
// for(Double d : c) {
// System.out.println(d);
// }
// }
//
// public static void print(String[] b) {
// for(String s : b) {
// System.out.println(s);
// }
// }
//
// public static void print(Integer[] a) {
// //使用普通循环遍历数组比较复杂,引入高效for循环
// //普通循环的好处是可以控制循环的步长(怎么变化)
// for (int i = 0; i < a.length; i=i+2) {
// System.out.println(a[i]);
// }
// /**
// * 高效for/foreach循环–如果只是单纯的从头到尾的遍历,使用增强for循环
// * 好处:比普通的for循环写法简便,而且效率高
// * 坏处:没有办法按照下标来操作值,只能从头到尾依次遍历
// * 语法:for(1 2 : 3){代码块} 3是要遍历的数据 1是遍历后得到的数据的类型 2是遍历起的数据名
// */
// for(Integer i : a) {
// System.out.print(i);
// }
// }
}
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2 Collection接口
2.1 集合前言
Java语言的java.util包中提供了一些集合类,这些集合类又称之为容器
提到容器不难想到数组,集合类与数组最主要的不同之处是,数组的长度是固定的,集合的长度是可变的，而数组的访问方式比较单一,插入/删除等操作比较繁琐,而集合的访问方式比较灵活
常用的集合类有List集合,Set集合,Map集合,其中List集合与Set集合继承了Collection接口,各个接口还提供了不同的实现类.
2.2 集合概念
集合的英文名称是Collection,是用来存放对象的数据结构,而且长度可变,可以存放不同类型的对象,并且还提供了一组操作成批对象的方法.Collection接口层次结构 中的根接口,接口不能直接使用,但是该接口提供了添加元素/删除元素/管理元素的父接口公共方法.
由于List接口与Set接口都继承了Collection接口,因此这些方法对于List集合和Set集合是通用的.
2.3 集合的继承结构
Collection接口
List 接口【数据有下标，有序，可重复】ArrayList子类
LinkedList子类
Set 接口【数据无下标，无序，不可重复】HashSet子类
Map 接口【键值对的方式寸数据】HashMap子类
2.4 Collection方法速查表
2.4 练习:Collection接口测试
创建包: cn.tedu.collection
创建类: TestCollection.java
package cn.tedu.colletion;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
/*本类用来测试Collection接口/
public class TestColletion {
public static void main(String[] args) {
//1.创建Collection接口相关对象
//Collection c = new Collection();//报错,因为Collection是接口不能实例化new
/*1.<Integer>是泛型,用来约束集合中的元素的类型,只能写引用类型,不能是基本类型/
Collection<Integer> c = new ArrayList<Integer>();
<span class="token comment">//2.1测试常用方法--对于单个集合的方法</span>
c<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
c<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
c<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">300</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
c<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">400</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
c<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">500</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>c<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//直接打印查看集合中的元素</span>
<span class="token comment">//c.clear();//清空集合中的元素</span>
<span class="token comment">//System.out.println(c);</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> c<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token number">300</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//true,判断集合中是否包含元素300</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> c<span class="token punctuation">.</span><span class="token function">hashCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//127240651,返回集合对应的哈希码值</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> c<span class="token punctuation">.</span><span class="token function">isEmpty</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//false,判断集合是否为空</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> c<span class="token punctuation">.</span><span class="token function">remove</span><span class="token punctuation">(</span><span class="token number">100</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//true,移出集合中的元素100,移出成功返回true</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> c <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//[200, 300, 400, 500],100被成功移除</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> c<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//4,获取集合的元素个数/类似数组长度</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> c<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//false,判断是否与100相等</span>
<span class="token comment">/**接返回值类型快捷键:Shift+alt+L*/</span>
Object<span class="token punctuation">[</span><span class="token punctuation">]</span> array <span class="token operator">=</span> c<span class="token punctuation">.</span><span class="token function">toArray</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//把集合中的元素放入数组</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>Arrays<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span>array<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//使用数组的工具类查看数组中的元素内容</span>
<span class="token comment">//2.2测试常用方法--集合间的操作</span>
Collection<span class="token generics function"><span class="token punctuation"><</span>Integer<span class="token punctuation">></span></span> c2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics function"><span class="token punctuation"><</span>Integer<span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
c2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//给c2集合添加元素</span>
c2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">4</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//给c2集合添加元素</span>
c2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">6</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//给c2集合添加元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>c2<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//[2, 4, 6],直接打印查看c2集合的内容</span>
c<span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>c2<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//把c2集合添加到c集合中</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>c<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//[200, 300, 400, 500, 2, 4, 6],追加操作</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>c<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span>c2<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//false</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>c<span class="token punctuation">.</span><span class="token function">containsAll</span><span class="token punctuation">(</span>c2<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//true,查看c集合是否包含c2集合中的所有元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>c<span class="token punctuation">.</span><span class="token function">removeAll</span><span class="token punctuation">(</span>c2<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//true,删除c集合中属于c2集合的所有元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>c<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//[200, 300, 400, 500],查看c集合删除c2集合后的结果,正确删除</span>
<span class="token comment">//System.out.println(c.retainAll(c2));//true,删除c集合</span>
<span class="token comment">//System.out.println(c);//[]</span>
<span class="token comment">//2.3 用来遍历/迭代集合中的元素 Iterator<E> iterator()</span>
<span class="token comment">/**
* 1.如何获取迭代器 c.iterator()
* 2.判断集合是否有下个元素 it.hasNext()
* 3.获取当前迭代到的元素 it.next()
*/</span>
Iterator<span class="token generics function"><span class="token punctuation"><</span>Integer<span class="token punctuation">></span></span> it <span class="token operator">=</span> c<span class="token punctuation">.</span><span class="token function">iterator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//通过iterator迭代器,循环获取集合中的元素</span>
<span class="token keyword">while</span><span class="token punctuation">(</span>it<span class="token punctuation">.</span><span class="token function">hasNext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
<span class="token comment">//hasNext()用来判断集合中是否有下个元素,有就返回true,继续循环取值</span>
Integer num <span class="token operator">=</span> it<span class="token punctuation">.</span><span class="token function">next</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//next()用来获取迭代到的元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
}
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3 List接口
3.1 概述
有序的colletion(也称为序列).此接口的用户可以对列表中的每个元素的插入位置进行精确的控制,用户可以根据元素的整数索引(在列表中的位置)来访问元素,并搜索列表中的元素.
3.2 特点
- 元素都有下标
- 数据是有序的
- 允许存放重复的元素
3.3 List方法速查表
3.4 练习:List接口测试
创建包: cn.tedu.collection
创建类: TestList.java
package cn.tedu.colletion;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/*本类用于测试List接口/
public class TestList {
public static void main(String[] args) {
//1.创建List接口对象,注意此处创建的多态对象,List是接口,不能直接实例化
List<String> list = new ArrayList<String>();//注意导包:java.util…导包快捷键:Ctrl+Shift+O
<span class="token comment">//2.测试继承自Colletion接口的方法</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"大力娃"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"千顺娃"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"头铁娃"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"喷火娃"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"喷水娃"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"隐身娃"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"小紫娃"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//查看集合中的所有元素</span>
<span class="token comment">//list.clear();//清空集合</span>
<span class="token comment">//System.out.println(list);//[],集合已清空</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"**********我是一个无情的分界线**************"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token string">"大力娃"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//判断是否包含元素"大哥"</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span><span class="token string">"头铁娃"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//判断list对象是否与"二哥"相等</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">hashCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取集合的哈希码值</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">isEmpty</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//判断集合是否为空</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">remove</span><span class="token punctuation">(</span><span class="token string">"喷水娃"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//移除集合中的元素"五哥"</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//查看集合中的内容</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取集合的元素个数,类似于数组的长度</span>
<span class="token comment">//将集合中的元素存入数组中,打印需要使用数组的工具类Arrays</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> Arrays<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">toArray</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//[大哥, 二哥, 三哥, 四哥, 六哥, 七弟]</span>
<span class="token comment">//3.List接口的特有方法 -- 都是可以根据索引来操作的方式</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"小蝴蝶"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//追加在最后</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token string">"蝎子精"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//在指定索引处添加指定的元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取指定下标对应的元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token string">"小蝴蝶"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span><span class="token string">"小蝴蝶"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取指定元素第一次出现的索引</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">lastIndexOf</span><span class="token punctuation">(</span><span class="token string">"小蝴蝶"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取指定元素最后一次出现的索引</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">remove</span><span class="token punctuation">(</span><span class="token number">6</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//移除指定索引的元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token string">"妖精蛇"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//重置指定索引处位置的值</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
List<span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span> subList <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">subList</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//截取子串,[2,6)含头不含尾</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>subList<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//4.集合间的操作</span>
List<span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span> list2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"1"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"2"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"3"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span>list2<span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//把list2集合添加到list集合中</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">addAll</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span>list2<span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//把list2集合添加到list集合的指定位置处</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list <span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span>list2<span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//判断list集合是否有一个元素是list2</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">containsAll</span><span class="token punctuation">(</span>list2<span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//判断list集合是否包含list2集合中的所有元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">.</span><span class="token function">removeAll</span><span class="token punctuation">(</span>list2<span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//删除list集合中list2集合中的所有元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span> list<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
}
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3.5 练习:List接口测试2
创建包: cn.tedu.collection
创建类: TestList2.java
package cn.tedu.colletion;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
/*本类用于进一步测试List接口,注意导包:java.util/
public class TestList2 {
public static void main(String[] args) {
//1.创建List接口对象 导包快捷键:Ctrl+Shift+O
List<String> list = new ArrayList<String>();
<span class="token comment">//2.向集合中添加元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"喜羊羊"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"美羊羊"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"懒羊羊"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"沸羊羊"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"小肥羊"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"红太阳"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//3.测试集合的迭代</span>
<span class="token comment">/**
* 集合迭代的方式:
* 1.for循环
* 2.增强for循环
* 3.iterator
* 4.listIterator
* */</span>
<span class="token comment">//方式一:因为List集合是有序的,元素有下标,所以可以根据下标进行遍历</span>
<span class="token comment">//从何开始:0 到哪结束:list.size() 如何变化:i++</span>
<span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span> <span class="token punctuation">;</span> i<span class="token operator"><</span> list<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
<span class="token comment">//根据对应的下标来获取集合对应位置上的元素</span>
String s <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"***********我是一个无情的分割线1***************"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//方式二:普通for循环遍历效率低,可以通过foreach提高遍历效率</span>
<span class="token comment">//好处:语法简洁效率高 坏处:不能按照下标来处理数据</span>
<span class="token comment">//格式:for(1 2 : 3){循环体} 3是要遍历的数据 1和2是遍历得到的单个数据的类型 和 名字</span>
<span class="token keyword">for</span><span class="token punctuation">(</span>String s <span class="token operator">:</span> list<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span><span class="token comment">//s就是本次循环/遍历得到的集合中的元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"***********我是一个无情的分割线2***************"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//方式三:iterator() 是继承自父接口Collection的</span>
<span class="token comment">/**1.获取当前集合的迭代器*/</span>
Iterator<span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span> it <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">iterator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">/**由于不清楚要遍历的集合中有多少元素,所以我们使用的循环结构是While*/</span>
<span class="token keyword">while</span><span class="token punctuation">(</span>it<span class="token punctuation">.</span><span class="token function">hasNext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span><span class="token comment">//判断集合中是否有下个元素,如果有,返回true,继续遍历</span>
String s <span class="token operator">=</span> it<span class="token punctuation">.</span><span class="token function">next</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取对应的元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"***********我是一个无情的分割线3***************"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//方式四:listIterator()是List接口特有的</span>
<span class="token comment">//Iterator<E> Iterator --父接口 --hasNext() --next() --remove()</span>
<span class="token comment">//ListIterator<E> ListIterator --子接口,拥有父接口的方法,也有自己特有的方法(逆向迭代)</span>
<span class="token comment">//public interface ListIterator<E> extends Iterator<E></span>
ListIterator<span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span> it2 <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">listIterator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">while</span><span class="token punctuation">(</span>it2<span class="token punctuation">.</span><span class="token function">hasNext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span><span class="token comment">//判断是否还有数据</span>
String s <span class="token operator">=</span> it2<span class="token punctuation">.</span><span class="token function">next</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取当前遍历得到的数据</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token comment">//思考:方式3和方式4有什么区别?</span>
<span class="token comment">//3使用的是父接口中的Iterator 4使用的是子接口中的ListIterator</span>
<span class="token comment">//子接口拥有父接口的所有方法,除此之外,子接口也可以拥有自己特有的方法,目前是向前/逆向遍历</span>
<span class="token punctuation">}</span>
}
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4 ArrayList
4.1 概述
- 存在java.util包中
- 内部是用数组结构存放数据,封装数组的操作,每个对象都有下标
- 内部数组默认的初始容量是10,如果不够会以1.5倍的容量增长
- 查询快,增删数据效率会低
4.2 创建对象
4.3 练习:ArrayList测试
创建包: cn.tedu.collection
创建类: TestArrayList.java
package cn.tedu.colletion;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.ListIterator;
/*本类用于测试ArrayList相关内容/
public class TestArrayList {
public static void main(String[] args) {
//1.创建对象,使用的是无参构造
//底层会自动帮我们创建数组存放对象,并且数据的初始容量是10
ArrayList<Integer> list = new ArrayList();//简写方式
<span class="token comment">//2.放入数据进行测试常用方法</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">100</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">300</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">400</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">300</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//向集合中添加元素</span>
list<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span><span class="token number">777</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//在指定下标处新增元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//list.clear();//清空集合</span>
<span class="token comment">//System.out.println(list);</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">contains</span><span class="token punctuation">(</span><span class="token number">300</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//true,判断集合是否包含元素300</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//777,获取集合中指定下标位置上的元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">indexOf</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//2,判断集合中指定元素第一次出现的下标</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">lastIndexOf</span><span class="token punctuation">(</span><span class="token number">200</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//6,判断集合中指定元素最后一次出现的下标</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">isEmpty</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//false,判断集合是否为空</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">remove</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//100,移除集合中指定下标对应着的元素,移除成功,返回被移除的元素</span>
<span class="token comment">/**
*Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 300, Size: 6
*这是根据下标来删除元素的,而此集合没有下标300,最大下标为6,所以会数组下标越界
*System.out.println(list.remove(300));--错误
*如果想根据具体的元素内容移除元素,需要先把int类型的数据转成Integer数据类型
* * */</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">remove</span><span class="token punctuation">(</span>Integer<span class="token punctuation">.</span><span class="token function">valueOf</span><span class="token punctuation">(</span><span class="token number">300</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//true</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">77</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//更改集合中对应下标上元素的值</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>Arrays<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">toArray</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//将集合元素存入数组,打印数组的具体值</span>
<span class="token comment">//4种迭代方式</span>
<span class="token comment">//方式1:for循环</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"方式1"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//开始:0 结束:最大下标(集合长度-1) 变化:++</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> list<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">print</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//根据下标获取对应下标位置上的元素</span>
<span class="token punctuation">}</span>
<span class="token comment">//方式2:增强for循环</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"方式2"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span>Integer i <span class="token operator">:</span> list<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span><span class="token comment">//遍历list集合,每次循环得到的元素是Integer类型的i</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">print</span><span class="token punctuation">(</span>i<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//打印每次循环到的集合元素</span>
<span class="token punctuation">}</span>
<span class="token comment">//方式3:Iterator</span>
<span class="token comment">/**1.获取迭代器 2.判断是否还有元素(一般用来做循环条件) 3.获取当前遍历到的元素*/</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"方式3"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Iterator<span class="token generics function"><span class="token punctuation"><</span>Integer<span class="token punctuation">></span></span> it <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">iterator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取集合用来迭代的迭代器,此迭代器是继承自Collection接口中的</span>
<span class="token keyword">while</span><span class="token punctuation">(</span>it<span class="token punctuation">.</span><span class="token function">hasNext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span><span class="token comment">//通过迭代器来判断集合中是否还有元素,如果有,继续迭代,如果没有,结束循环</span>
Integer num <span class="token operator">=</span> it<span class="token punctuation">.</span><span class="token function">next</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取当前遍历到的集合元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//打印当前遍历到的集合元素</span>
<span class="token punctuation">}</span>
<span class="token comment">//方式4:ListIterator</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"方式4"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
ListIterator<span class="token generics function"><span class="token punctuation"><</span>Integer<span class="token punctuation">></span></span> it2 <span class="token operator">=</span> list<span class="token punctuation">.</span><span class="token function">listIterator</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取集合用来迭代的迭代器,此迭代器是List接口中的迭代器</span>
<span class="token keyword">while</span><span class="token punctuation">(</span>it2<span class="token punctuation">.</span><span class="token function">hasNext</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span><span class="token comment">//通过迭代器来判断集合中是否还有元素,如果有继续迭代,如果没有,结束循环</span>
Integer s2 <span class="token operator">=</span> it2<span class="token punctuation">.</span><span class="token function">next</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取当前遍历到的集合元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">print</span><span class="token punctuation">(</span>s2<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//打印当前遍历到的集合元素</span>
<span class="token punctuation">}</span>
}
}
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5 LinkedList
5.1 概述
链表,两端效率高,底层就是链表实现的
5.2 创建对象
LinkedList() 构造一个空列表
5.3 常用方法
void addFirst(E e) 将指定元素插入此列表的开头
void addLast(E e) 将指定元素添加到此列表的结尾
E getFirst() 返回此列表的第一个元素
E getLast() 返回此列表的最后一个元素
E removeFirst()移除并返回此列表的第一个元素
E removeLast() 移除并返回此列表的最后一个元素
E element() 获取但不移除此列表的头（第一个元素）
boolean offer(E e) 将指定元素添加到此列表的末尾（最后一个元素）
boolean offerFirst(E e) 在此列表的开头插入指定的元素
boolean offerLast(E e) 在此列表末尾插入指定的元素
E peek() 获取但不移除此列表的头（第一个元素）
E peekFirst() 获取但不移除此列表的第一个元素；如果此列表为空，则返回 null
E peekLast() 获取但不移除此列表的最后一个元素；如果此列表为空，则返回 null
E poll()获取并移除此列表的头（第一个元素）
E pollFirst() 获取并移除此列表的第一个元素；如果此列表为空，则返回 null
E pollLast() 获取并移除此列表的最后一个元素；如果此列表为空，则返回 null
5.4练习:LinkedList测试
创建包: cn.tedu.collection
创建类: TestLinkedList.java
package cn.tedu.colletion;
import java.util.LinkedList;
/*本类用于测试LinkedList的相关测试/
public class TestLinkedList {
public static void main(String[] args) {
//1.创建对象
LinkedList<String> list = new LinkedList();
//2.添加数据
list.add(“孙悟空”);
list.add(“猪八戒”);
list.add(“唐三藏”);
list.add(“沙师弟”);
list.add(“白龙马”);
System.out.println(list);
<span class="token comment">//3.1自行测试从collection继承过来的共性方法测试</span>
<span class="token comment">//3.2 LinkedList特有方法测试</span>
list<span class="token punctuation">.</span><span class="token function">addFirst</span><span class="token punctuation">(</span><span class="token string">"蜘蛛精"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//添加首元素</span>
list<span class="token punctuation">.</span><span class="token function">addLast</span><span class="token punctuation">(</span><span class="token string">"玉兔精"</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//添加尾元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">getFirst</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取首元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">getLast</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取尾元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">removeFirst</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//移除首元素,成功移除会返回移除的数据</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">.</span><span class="token function">removeLast</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//移除尾元素,成功移除会返回移除的数据</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//4.其他测试</span>
<span class="token comment">//4.1创建对象</span>
LinkedList<span class="token generics function"><span class="token punctuation"><</span>String<span class="token punctuation">></span></span> list2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">LinkedList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//4.2添加数据</span>
list2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"水浒传"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"三国演义"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"西游记"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
list2<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"红楼梦"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">)</span><span class="token punctuation">;</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">element</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取但不移除此列表的首元素(第一个元素)</span>
<span class="token comment">/**别名:查询系列*/</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">peek</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取但不移除此列表的首元素(第一个元素)</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">peekFirst</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取但不移除此列表的首元素(第一个元素)</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">peekLast</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取但不移除此列表的尾元素(最后一个元素)</span>
<span class="token comment">/**别名:新增系列*/</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">offer</span><span class="token punctuation">(</span><span class="token string">"遮天"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//将指定元素添加到列表末尾</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">offerFirst</span><span class="token punctuation">(</span><span class="token string">"斗罗大陆"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//将指定元素插入列表开头</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">offerLast</span><span class="token punctuation">(</span><span class="token string">"斗破苍穹"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//将指定元素插入列表末尾</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">/**别名:移除系列*/</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">poll</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取并且移除此列表的首元素(第一个元素),成功移除,返回移除元素</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">pollFirst</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取并且移除此列表的首元素(第一个元素),成功移除,返回移除元素,如果此列表为空,则返回null</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">.</span><span class="token function">pollLast</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//获取并且移除此列表的尾元素(最后一个元素),成功移除,返回移除元素,如果此列表为空,则返回null</span>
System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>list2<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
}
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6 扩展: ArrayList扩容
ArrayList相当于在没指定initialCapacity时就是会使用延迟分配对象数组空间，当第一次插入元素时才分配10（默认）个对象空间。假如有20个数据需要添加，那么会分别在第一次的时候，将ArrayList的容量变为10；之后扩容会按照1.5倍增长。也就是当添加第11个数据的时候，Arraylist继续扩容变为10*1.5=15；当添加第16个数据时，继续扩容变为15 * 1.5 =22个
ArrayList没有对外暴露其容量个数，查看源码我们可以知道，实际其值存放在elementData对象数组中，那我们只需拿到这个数组的长度，观察其值变化了几次就知道其扩容了多少次。怎么获取呢？只能用反射技术了。
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