This code snippet shows you how to loop or iterate a Map or HashMap in Java.


	Map<String, String> map = new HashMap<String, String>();
	map.put("1", "Jan");
	map.put("2", "Feb");
	map.put("3", "Mar");
	
	//loop a Map
	for (Map.Entry<String, String> entry : map.entrySet()) {
		System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());
	}
		
	//Java 8 only, forEach and Lambda
	map.forEach((k,v)->System.out.println("Key : " + k + " Value : " + v));

Output


    Key : 1 Value :Jan
    Key : 2 Value :Feb
    Key : 3 Value :Mar

    Key : 1 Value :Jan
    Key : 2 Value :Feb
    Key : 3 Value :Mar

Full Example

There are 4 ways to loop or iterate a Map in Java.

LoopMap.java

package com.mkyong;

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

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");

		// Map -> Set -> Iterator -> Map.Entry -> troublesome, not recommend!
		System.out.println("\nExample 1...");
		Iterator<Entry<String,String>> iterator = map.entrySet().iterator();
		while (iterator.hasNext()) {
			Map.Entry<String,String> entry = (Map.Entry<String,String>) iterator.next();
			System.out.println("Key : " + entry.getKey() + " Value :" + entry.getValue());
		}
		
		// more elegant way, this should be the standard way, recommend!
		System.out.println("\nExample 2...");
		for (Map.Entry<String, String> entry : map.entrySet()) {
			System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());
		}

		// weired, but works anyway, not recommend!
		System.out.println("\nExample 3...");
		for (Object key : map.keySet()) {
			System.out.println("Key : " + key.toString() + " Value : " + map.get(key));
		}
		
		//Java 8 only, forEach and Lambda. recommend!
		System.out.println("\nExample 4...");
		map.forEach((k,v)->System.out.println("Key : " + k + " Value : " + v));
	}

}

Output


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

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

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

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

References

  1. java.util.Iterator JavaDoc
  2. java.util.Map JavaDoc
  3. Java 8 forEach examples
  4. Iterating over collections in Java 8