java基础之集合

<wbr><wbr> Java 的集合类它可以存储数量不等的多个对象. 或者也可以理解为特殊的容器(如前面学过的数组,集合的功能要更为强大)</wbr></wbr>

Java集合大致分为三大类 Set list Map三类体系
其中Set代表无序不可以重复的集合，List代表有序的重复的集合，Map代表具有映射关系的集合。jdk1.5增加了Queue体系的集合
代表队列集合的实现。
<wbr><wbr><wbr> Java的集合类主要由两个接口派生出:Cllection和Map，Collection和Map是Java集合框架的根接口，这两个接口又包含了一些子接口或实现类。<br><wbr><wbr><wbr> 一 Colllection和Iterator接口<br> Collcetion接口是List Se和Queue接口的父亲接口，该接口定义的方法能操作这三个集合元素，Cllection接口定义了如下操作集合的元素的方法<br><wbr><wbr><wbr><wbr><wbr><wbr> 1 boolean add(Object o):该方法用于向集合里添加一个元素，如果集合对象被添加操作改变了则返回true;<br><wbr><wbr><wbr><wbr><wbr><wbr> 2 boolean addAll(Collection c):该方法把集合里所有的元素添加到指定的集合里，如果集合对象被添加操作改变了则返回true;<br><wbr><wbr><wbr><wbr><wbr><wbr> 3 void clear():清除集合里所有的元素，使集合的长度变为0；<br><wbr><wbr><wbr><wbr><wbr><wbr> 4 boolean contains(Object o):返回集合里是否包含指定的元素；<br><wbr><wbr><wbr><wbr><wbr><wbr> 5 boolean containsAll(Cllocetion c）返回集合里是否包含集合c的全部元素；<br><wbr><wbr><wbr><wbr><wbr><wbr> 6 boolean isEmpty() 返回集合是否为空，当集合长度为0返回true；<br><wbr><wbr><wbr><wbr><wbr><wbr> 7 Iterator iterator():返回iterator对象遍历集合；<br><wbr><wbr><wbr><wbr><wbr><wbr> 8 boolean remove(Object o)删除集合中指定的元素o，如果有多个o元素这些元素将都被删除；<br><wbr><wbr><wbr><wbr><wbr><wbr> 9 boolean remove (Collection c):从集合中删除集合c里指定的全部元素；<br><wbr><wbr><wbr><wbr><wbr><wbr> 10 int size():返回集合里所有元素的个数；<br><wbr><wbr><wbr><wbr><wbr><wbr> 11 Object[]toArray() 把集合转换为数组，集合的元素变成对应的数组元素；<br> 下面是测试这些方法的简单代码：<wbr><wbr><wbr><br> import java.util.*;<br> public class TestCollection<br> {<br><wbr><wbr><wbr> public static void main(String[] args)<br><wbr><wbr><wbr> {<br><wbr><wbr><wbr><wbr><wbr><wbr> Collection c = new ArrayList();<br><wbr><wbr><wbr><wbr><wbr><wbr> //添加元素<br><wbr><wbr><wbr><wbr><wbr><wbr> c.add("swk");<br><wbr><wbr><wbr><wbr><wbr><wbr> //虽然集合里不能放基本类型的值，但Java支持自动装箱<br><wbr><wbr><wbr><wbr><wbr><wbr> c.add(6);<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("c集合的元素个数为:" + c.size());<br><wbr><wbr><wbr><wbr><wbr><wbr> //删除指定元素<br><wbr><wbr><wbr><wbr><wbr><wbr> c.remove(6);<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("c集合的元素个数为:" + c.size());<br><wbr><wbr><wbr><wbr><wbr><wbr> //判断是否包含指定字符串<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("c集合的是否包含孙悟空字符串:" + c.contains("swk"));<br><wbr><wbr><wbr><wbr><wbr><wbr> c.add("J2EE企业应用实战");<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("c集合的元素：" + c);<br><wbr><wbr><wbr><wbr><wbr><wbr> Collection books = new HashSet();<br><wbr><wbr><wbr><wbr><wbr><wbr> books.add("轻量级J2EE企业应用实战");<br><wbr><wbr><wbr><wbr><wbr><wbr> books.add("Struts2权威指南");<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("c集合是否完全包含books集合？" + c.containsAll(books));<br><wbr><wbr><wbr><wbr><wbr><wbr> //用c集合减去books集合里的元素<br><wbr><wbr><wbr><wbr><wbr><wbr> c.removeAll(books);<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("c集合的元素：" + c);<br><wbr><wbr><wbr><wbr><wbr><wbr> //删除c集合里所有元素<br><wbr><wbr><wbr><wbr><wbr><wbr> c.clear();<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("c集合的元素：" + c);<br><wbr><wbr><wbr><wbr><wbr><wbr> //books集合里只剩下c集合里也同时包含的元素<br><wbr><wbr><wbr><wbr><wbr><wbr> books.retainAll(c);<br><wbr><wbr><wbr><wbr><wbr><wbr> System.out.println("books集合的元素:" + books);<br><wbr><wbr><wbr> }<br> }<br> 使用Iterator 接口遍历集合<br><wbr> Iterator接口也是java集合框架的成员与其他集合不一样，该集合是用来遍历集合元素的<br><wbr> Iterator对象也被称为迭代器；<br><wbr> Iterator接口提供了下面主要的三个方法<br><wbr> boolean hasNext();如果迭代的集合还有没遍历的则返回true;<br><wbr> boolean next()返回集合里下一个元素；<br><wbr> void remove()删除集合里上一次next方法返回的元素；<br><wbr> 参考代码：<br><wbr> public class TestIterator<br></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>