java集合框架

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本文概述了Java集合框架的重要性，介绍了Collection、Map、Queue和Collections工具类，详细讲解了ArrayList、LinkedList、Vector的区别以及排序方法，包括自定义Comparator和实现Comparable接口。

集合框架

为什么学集合

变量-----》数组-----》集合

集合是动态数组，长度可变
集合提供了更多样的存储结构（key-value）

java框架的认知

Java集合框架分4个体系：

Collection 集合
Map 集合
Queue 队列
Collections 集合工具类

不同集合特点不同

能否重复
是否有序

collection集合

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ArrayList: 数组的存储结构非线程安全效率高

Vector: 数组存储结构线程安全效率低

LinkedList：双向链表存储结构遍历时效率低增加、删除时效率高。

每个元素除了存储值，还需存储上、下元素的地址

特点：遍历效率低怎加、删除元素效率高

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深入解析：

源码解析

ArrayList底层是数组，会发生数组的复制

集合排序

Collections.sort();//字符串、数值

如果存放的是对象

Collections.sort(list,排序规则)

排序规则： new Comparator(){}

package com.qf.pro2103.day16;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import com.qf.pro2103.util.ListUtil;

public class Demo6 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ArrayList<Student> stus=new ArrayList<Student>();
		Student s1=new Student("qf001","贾玉堃",25);
		Student s2=new Student("qf002","张磊",18);
		Student s3=new Student("qf003","哈淳鑫",20);
		Student s4=new Student("qf004","胡锦辉",19);
		stus.add(s1);
		stus.add(s2);
		stus.add(s3);
		stus.add(s4);
		//按年年龄升序排序
		Comparator<Student> comparator=new Comparator<Student>(){

			@Override
			public int compare(Student o1, Student o2) {
				// TODO Auto-generated method stub
				//return o2.getAge()-o1.getAge();
				return o1.getStuName().compareTo(o2.getStuName());
			}
			
		};
		//排序
		Collections.sort(stus,comparator);
		//打印集合
		ListUtil.printList(stus);
	}

}

排序方式2：类去实现Comparable—compareTo

package com.qf.pro2103.day16;

public class Student implements Comparable<Student> {
	
	public Student() {
		super();
	}
	
	public Student(String stuNo, String stuName) {
		super();
		this.stuNo = stuNo;
		this.stuName = stuName;
	}
	
	public Student(String stuNo, String stuName, int age) {
		super();
		this.stuNo = stuNo;
		this.stuName = stuName;
		this.age = age;
	}

	@Override
	public String toString() {
		return "Student [stuNo=" + stuNo + ", stuName=" + stuName + ", age=" + age + "]";
	}

	private String stuNo;
	private String stuName;
	private int age;
	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getStuNo() {
		return stuNo;
	}
	public void setStuNo(String stuNo) {
		this.stuNo = stuNo;
	}
	public String getStuName() {
		return stuName;
	}
	public void setStuName(String stuName) {
		this.stuName = stuName;
	}

	@Override
	public int compareTo(Student o) {
		// TODO Auto-generated method stub
		//先按年龄排序
		int n1=this.age-o.age;
		//int n2=this.stuName.compareTo(o.stuName);
		int n2=o.stuName.compareTo(this.stuName);
		
		return n1==0?n2:n1;
	}
}

package com.qf.pro2103.day16;

import java.util.ArrayList;
import java.util.Collections;

import com.qf.pro2103.util.ListUtil;

public class Demo7 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		ArrayList<Student> stus=new ArrayList<Student>();
		Student s1=new Student("qf001","zzz",25);
		Student s2=new Student("qf002","lll",20);
		Student s3=new Student("qf003","hahaha",20);
		Student s4=new Student("qf004","ccc",19);
		stus.add(s1);
		stus.add(s2);
		stus.add(s3);
		stus.add(s4);
		Collections.sort(stus);
		ListUtil.printList(stus);
		
	}

}