Java 8 Map : compute()


Map compute() function computes a mapping for the specified key and its current mapped value.

It uses a BiFunction for the mapping.

Syntax :

default V compute(K key, BiFunction<? super K,? super V,? extends V> remappingFunction)

Java8 compute() example

package com.topjavatutorial;

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

public class TestMap5 {

  public static void main(String[] args) {
    Map<String, Integer> map = new HashMap<String, Integer>();
    map.put("A", 1);
    map.put("B", 2);
    map.put("C", 3);

    map.compute("A", (k, v) -> (v==null ? 0 : v+1));

    map.compute("D", (k, v) -> (v==null ? 0 : v+1));

Output :

{A=1, B=2, C=3}
{A=2, B=2, C=3}
{A=2, B=2, C=3, D=0}

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