Java – How to Iterate a HashMap
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
Map<Integer,Lis>map
How iterate this map using java 8
Or using stream ().forEach()