How to Iterate Through HashMap in Java

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Mohammad Irfan Feb 02, 2024
Java Java HashMap
  1. Iterate Through HashMap Using entrySet() Method in Java
  2. Iterate Through HashMap Using foreach in Java
  3. Iterate Through HashMap Using keySet() Method in Java
  4. Iterate Through HashMap Using forEach() Method in Java
  5. Iterate Through HashMap Using stream and forEach() Method in Java
How to Iterate Through HashMap in Java

This tutorial introduces how to iterate through HashMap in Java and lists some example codes to understand it.

There are several ways to iterate HashMap, here we use keySet(), entrySet(), and forEach() method, etc. Let’s see the examples.

Iterate Through HashMap Using entrySet() Method in Java

The entrySet() method is used to get set a view of the mappings contained in the map. We collect the set view into the iterator and iterate using the while loop. See the example below.

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

public class SimpleTesting {
  public static void main(String[] args) {
    Map<Integer, Integer> map = new HashMap<>();
    map.put(2, 1020);
    map.put(3, 300);
    map.put(1, 100);
    map.put(5, 500);
    Iterator it = map.entrySet().iterator();
    while (it.hasNext()) {
      Map.Entry<Integer, Integer> entry = (Map.Entry) it.next();
      System.out.println(entry.getKey() + " = " + entry.getValue());
    }
  }
}

Output:

1 = 10
2 = 1020
3 = 300
5 = 500

Iterate Through HashMap Using foreach in Java

This is another solution to iterate the HasMap. Here, we use a for-each loop to iterate the elements of HashMap. See the example below.

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

public class SimpleTesting {
  public static void main(String[] args) {
    Map<Integer, Integer> map = new HashMap<>();
    map.put(2, 1020);
    map.put(3, 300);
    map.put(1, 100);
    map.put(5, 500);
    for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
      System.out.println(entry.getKey() + " = " + entry.getValue());
    }
  }
}

Output:

1 = 10
2 = 1020
3 = 300
5 = 500

Iterate Through HashMap Using keySet() Method in Java

The keySet() method is used to collect all the keys and create a set that further could be used to iterate element of the HashMap. See the example below.

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

public class SimpleTesting {
  public static void main(String[] args) {
    Map<Integer, Integer> map = new HashMap<>();
    map.put(2, 1020);
    map.put(3, 300);
    map.put(1, 100);
    map.put(5, 500);
    for (Integer key : map.keySet()) {
      System.out.println(key + " = " + map.get(key));
    }
  }
}

Output:

1 = 10
2 = 1020
3 = 300
5 = 500

Iterate Through HashMap Using forEach() Method in Java

We can use the forEach() method to iterate the elements of HashMap. The forEach() method is a new method introduced into Java 8 and available into Iteratable and Stream interfaces. See the example below.

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

public class SimpleTesting {
  public static void main(String[] args) {
    Map<Integer, Integer> map = new HashMap<>();
    map.put(2, 1020);
    map.put(3, 300);
    map.put(1, 100);
    map.put(5, 500);
    map.forEach((key, value) -> { System.out.println(key + " = " + value); });
  }
}

Output:

1 = 10
2 = 1020
3 = 300
5 = 500

Iterate Through HashMap Using stream and forEach() Method in Java

We can use the stream to iterate the elements. Here, we use entrySet() to collect map elements that further traverse through the forEach() method of the stream.

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

public class SimpleTesting {
  public static void main(String[] args) {
    Map<Integer, String> map = new HashMap<>();
    map.put(10, "Ten");
    map.put(100, "Hundred");
    map.put(1000, "Thousand");
    map.entrySet().stream().forEach(System.out::println);
  }
}

Output:

1 = 10
2 = 1020
3 = 300
5 = 500

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