java 例子分析

例子一

public class Test1 {

	public static void main(String[] args) {

		Map map = new HashMap();
		List violateList = new ArrayList();
		map.put("violateList", violateList);
		System.out.println(map);

		violateList = getList();
		System.out.println(violateList);

		System.out.println(map);

		/**
		 * 输出： 
		 * {violateList=[]} 
		 * [a, b, c, d] 
		 * {violateList=[]}
		 * 
		 * 原因：map的key指向violateList变量，本质是指向了violateList变量对应的对象体；
		 * violateList指向其他对象体时，不影响map的； 例子二可以证明
		 */

	}

	public static List getList() {
		List list = new ArrayList();

		list.add("a");
		list.add("b");
		list.add("c");
		list.add("d");
		return list;
	}
}

　　

例子二
package test2016;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Test2 {

	public static void main(String[] args) {

		Map map = new HashMap();
		List violateList = new ArrayList();
		map.put("violateList", violateList);
		System.out.println(map);

		violateList.add("1");
		violateList.add("2");
		violateList.add("3");
		violateList.add("4");

		System.out.println(violateList);

		System.out.println(map);

		/**
		 * 输出：
		 * {violateList=[]} 
		 * [1, 2, 3, 4] 
		 * {violateList=[1, 2, 3, 4]}
		 */

	}

}