一段代码让你理解set和list的区别

先看代码，最好亲自写

package com.leilei;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

public class HashSetTest {

	public static void main(String[] args) {
		
		List lists = new ArrayList();
		lists.add("1");
		lists.add("2");
		lists.add("3");
		lists.add("2");
		System.out.println(lists);
		for(Object object:lists){
			String list = (String)object;
			System.out.println(list);
		}
		System.out.println("------------------------");
		// 创建集合添加元素
		Set books = new HashSet();
		books.add("1");
		books.add("2");
		books.add("3");
		books.add("3");
		System.out.println(books);
		//遍历集合
		for(Object object:books){
			String book = (String)object;
			System.out.println(book);
		}

	}

}

再看运行结果

----------------------------------------------------这里开始----------------------------------------------------------------

[1, 2, 3, 2]
1
2
3
2
------------------------
[3, 2, 1]
3
2
1

----------------------------------------------------这里结束----------------------------------------------------------------

结论：list存储有序可重复的对象，set存储无序不可重复的set，添加重复数据会失败。