Java Map

package javastudy;

import java.util.HashMap;
import java.util.Map;

public class TestMap {
	public static void main(String [] args ){
		Map<String, String> map = new HashMap<String, String>();
		map.put(String.valueOf(System.nanoTime())+"a", "1");
		map.put(String.valueOf(System.nanoTime())+"a", "2");
		map.put(String.valueOf(System.nanoTime())+"a", "3");
		
		for (Map.Entry<String, String> entry : map.entrySet()){
			System.out.print("key:"+entry.getKey()) ;
			System.out.println(" value:"+entry.getValue());
		}
		
		System.out.println("keys: "+map.keySet());
		System.out.println("values: "+map.values());
	}
}

结果

key:33869093351437a value:2
key:33869093363103a value:3
key:33869093271646a value:1
keys: [33869093351437a, 33869093363103a, 33869093271646a]
values: [2, 3, 1]

结论：

key--->set  不可有重复，输出的结果顺序有一定的随机性。

value-->collection