How To Loop A Map In Java

最新推荐文章于 2024-08-20 18:36:29 发布

转载最新推荐文章于 2024-08-20 18:36:29 发布 · 895 阅读

本文详细介绍了在Java中使用Map和HashMap进行遍历的方法，包括使用Iterator、集合转换以及for-each循环等手段，展示了不同方法的实现过程和优缺点。

Here are few ways to loop or iterate a Map or HashMap in Java.

package com.mkyong;
 
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
 
public class LoopMap {
 
  public static void main(String[] args) {
 
// initial a Map
Map<String, String> map = new HashMap<String, String>();
map.put("1", "Jan");
map.put("2", "Feb");
map.put("3", "Mar");
map.put("4", "Apr");
map.put("5", "May");
map.put("6", "Jun");
 
System.out.println("Example 1...");
// Map -> Set -> Iterator -> Map.Entry -> troublesome
Iterator iterator = map.entrySet().iterator();
while (iterator.hasNext()) {
Map.Entry mapEntry = (Map.Entry) iterator.next();
System.out.println("The key is: " + mapEntry.getKey()
+ ",value is :" + mapEntry.getValue());
}
 
System.out.println("Example 2...");
// more elegant way
for (Map.Entry<String, String> entry : map.entrySet()) {
System.out.println("Key : " + entry.getKey() + " Value : "
+ entry.getValue());
}
 
System.out.println("Example 3...");
// weired way, but works anyway
for (Object key : map.keySet()) {
System.out.println("Key : " + key.toString() + " Value : "
+ map.get(key));
}
 
  }
 
}

Output

Example 1...
The key is: 3,value is :Mar
The key is: 2,value is :Feb
The key is: 1,value is :Jan
The key is: 6,value is :Jun
The key is: 5,value is :May

The key is: 4,value is :Apr

Example 2...
Key : 3 Value : Mar
Key : 2 Value : Feb
Key : 1 Value : Jan
Key : 6 Value : Jun
Key : 5 Value : May

Key : 4 Value : Apr

Example 3...
Key : 3 Value : Mar
Key : 2 Value : Feb
Key : 1 Value : Jan
Key : 6 Value : Jun
Key : 5 Value : May
Key : 4 Value : Apr