Java中Map集合的遍历

package com.unionpay.service.channelbankcard.impl;


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


public class Test {
public static void main(String[] args) {
Map<String,String> map=new HashMap<String,String>();
map.put("key1", "value1");
map.put("key2", "value2");
map.put("key3", "value3");
map.put("key4", "value4");
///第一种：通过Map.keySet遍历key和value,普遍使用，二次取值 
for (String key : map.keySet()) {  
System.out.println("key= "+ key + " and value= " + map.get(key));  
}
//第二种  通过Map.entrySet使用iterator遍历key和value
Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();  
while (it.hasNext()) {  
Map.Entry<String, String> entry = it.next();  
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());  
}    
//第三种：推荐，尤其是容量大时  通过Map.entrySet遍历key和value
for (Map.Entry<String, String> entry : map.entrySet()) {  
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());  
}  
//第四种  通过Map.values()遍历所有的value，但不能遍历key
for (String v : map.values()) {  
System.out.println("value= " + v);  
}
}
}