Java Map的几种循环方式学习总结[通俗易懂]

全栈程序员-站长 • 2022年2月24日下午2:00 • 未分类 • 阅读 52

大家好，又见面了，我是全栈君。

1：根据JDK的新特性,用For循环Map,例如循环Map的Key

Map<Object , Object> map = new HashMap<Object, Object>();
		for (int i = 0; i < 10; i++) {
			map.put(i, i+1);
		}
		for (Object key : map.keySet()) {
			System.out.println("key = " + key);
		}

2:对整Map的key和value都进行循环,如下:

for(Map.Entry<String, Object> entry : paraMap.entrySet())    
{    
    System.out.println(entry.getKey()+": "+entry.getValue());    
}

3:使用Iterator

Iterator it = paraMap.entrySet().iterator();    
while (it.hasNext())     
{    
        Map.Entry map = (Map.Entry)it.next();    
        System.out.println(map .getKey() + " = " + map .getValue());    
 }

对上面的内容进行更新！将三种方式完整呈现！

package com.dufyun.javase.jihe;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

/**
 * 练习循环map集合中key和value的方法
 * @author aflyun
 * 
 *
 */
public class TestMap {
	
	   
	public static void main(String[] args) {
		Map<Object , Object> map = new HashMap<Object, Object>();
		for (int i = 0; i < 10; i++) {
			map.put(i, i+1);
		}
		
		firstLoopMap(map);
		secodnLoopMap(map);
		thirdLoopMap(map);
	}
	
	/**
	 * 1：循环 map 中的key<br/>
	 * 	 根据JDK的新特性,用For循环Map,例如循环Map的Key 和 value 
	 * @param map
	 */
	public static void firstLoopMap(Map<Object, Object> map) {
		for (Object key : map.keySet()) {
			System.out.println("key = " + key +"--value = " + map.get(key));
		}
	}
	/**
	 * 2：循环 map 中的key 和 value<br/>
	 * entrySet 
	 * @param map
	 */
	public static void secodnLoopMap(Map<Object , Object> map) {
		for (Map.Entry<Object, Object> entry : map.entrySet()) {
			System.out.println("key = " + entry.getKey() +"--value = " + entry.getValue());
		}
	}
	
	/**
	 * 3:循环Map的key 和value<br/>
	 * iterator
	 * @param map
	 */
	public static void thirdLoopMap(Map<Object, Object> map) {
		Iterator it = map.entrySet().iterator();
		while(it.hasNext()){
			Map.Entry<Object, Object> m = (Entry<Object, Object>) it.next();
			System.out.println("key = " + m.getKey() +"---value = "+ m.getValue());
		}
				
	}
}

输出的内容：

key = 0---value = 1
key = 1---value = 2
key = 2---value = 3
key = 3---value = 4
key = 4---value = 5
key = 5---value = 6
key = 6---value = 7
key = 7---value = 8
key = 8---value = 9
key = 9---value = 10

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