How to Increment a Map Value in Java 8?

To Increment a Map Value in Java 8, we are using HashMap merge() Method.

• The HashMap merge() method used to compute the new updated value that will replace the existing value in the Map.
• Here we iterate a for loop from 0 to 4.
• Inside Merge method, we mention “total count” as a key and value will be increment each time during iteration using Integer::sum method.
• Integer::sum method handles update or add values associated with keys.
• Now print the output.

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

public class MergeTest {
	public static void main(String[] args) {
		Map<String, Integer> map = new HashMap<String, Integer>();
		for (int i = 0; i < 4; i++) {
			map.merge("total count", 1, Integer::sum);
		}
		System.out.println(map);
	}
}

Output :-
{total count=4}