Java 8 Map : computeIfPresent
computeIfPresent()
default V computeIfPresent(K key, BiFunction<? super K,? super V,? extends V> remappingFunction)
If the value for the specified key is present and non-null, it attempts to compute a new mapping given the key and its current mapped value.
If the function returns null, the mapping is removed.
computeIfPresent() uses a BiFunction . The Function runs only if the specified key is present in the map.
package com.topjavatutorial;
import java.util.HashMap;
import java.util.Map;
import java.util.function.BiFunction;
public class TestMap2 {
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);
System.out.println(map);
BiFunction<String, Integer, Integer> biFunction = (k, v) -> v + 1;
// "A" is already present in map, so its value will be incremented
map.computeIfPresent("A", biFunction);
System.out.println(map);
// Since "D" is not present in map, the computation won't occur
map.computeIfPresent("D", biFunction);
System.out.println(map);
}
}
Output :
{A=1, B=2, C=3}
{A=2, B=2, C=3}
{A=2, B=2, C=3}
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