Java How to Iterate a HashMap
By:Roy.LiuLast updated:2019-08-11
In Java, there are 3 ways to loop or iterate a HashMap
1. If possible, always uses the Java 8 forEach.
Map<String, String> map = new HashMap<>(); map.forEach((key, value) -> System.out.println("[Key] : " + key + " [Value] : " + value));
2. Normal for loop in entrySet()
Map<String, String> map = new HashMap<>(); for (Map.Entry<String, String> entry : map.entrySet()) { System.out.println("[Key] : " + entry.getKey() + " [Value] : " + entry.getValue());
3. Iterator, classic.
Map<String, String> map = new HashMap<>(); Iterator iter = map.entrySet().iterator(); while (iter.hasNext()) { Map.Entry entry = (Map.Entry) iter.next(); System.out.println("[Key] : " + entry.getKey() + " [Value] : " + entry.getValue());
HashMap example
A full example, just for reference.
HashMapExample.java
package com.mkyong.calculator; import java.util.HashMap; import java.util.Iterator; import java.util.Map; public class HashMapExample { public static void main(String[] args) { Map<String, Integer> map = new HashMap<>(); map.put("web", 1024); map.put("database", 2048); map.put("static", 5120); System.out.println("Java 8 forEach loop"); map.forEach((key, value) -> System.out.println("[Key] : " + key + " [Value] : " + value)); System.out.println("for entrySet()"); for (Map.Entry<String, Integer> entry : map.entrySet()) { System.out.println("[Key] : " + entry.getKey() + " [Value] : " + entry.getValue()); System.out.println("Iterator"); Iterator iter = map.entrySet().iterator(); while (iter.hasNext()) { Map.Entry entry = (Map.Entry) iter.next(); System.out.println("[Key] : " + entry.getKey() + " [Value] : " + entry.getValue());
Output
Java 8 forEach loop [Key] : database [Value] : 2048 [Key] : static [Value] : 5120 [Key] : web [Value] : 1024 for entrySet() [Key] : database [Value] : 2048 [Key] : static [Value] : 5120 [Key] : web [Value] : 1024 Iterator [Key] : database [Value] : 2048 [Key] : static [Value] : 5120 [Key] : web [Value] : 1024
From:一号门
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