Java ConcurrentHashMap: compute() Example
February 10, 2022
compute() method of Java ConcurrentHashMap class.
Find the Java doc of
compute method.
V compute(K key, BiFunction<? super K,? super V,? extends V> remappingFunction)
compute method computes the value for the specified key. It updates the value with new computed value corresponding to specified key.
2. The
compute method invocation is performed atomically.
3. The supplied
BiFunction is invoked exactly once per invocation of compute method.
4. Parameters:
key - Key for which the corresponding value is to be computed.
remappingFunction - The
BiFunction to compute the value.
5. Returns: The
compute method returns the new computed value. It returns null if there is no corresponding value for the specified key.
6. Throws: The
compute method can throw following exceptions.
NullPointerException: If specified key or provided remappingFunction is null.
IllegalStateException: If computation is recursive.
RuntimeException: If remappingFunction throws
RuntimeException, then compute method will also throw RuntimeException.
Example
ComputeDemo.java
package com.concretepage;
import java.util.concurrent.ConcurrentHashMap;
public class ComputeDemo {
public static void main(String[] args) {
System.out.println("--- Example-1 ---");
ConcurrentHashMap<String, Integer> conMap1 = new ConcurrentHashMap<>();
conMap1.put("Mahesh", 22);
conMap1.put("Nilesh", 25);
Integer v1 = conMap1.compute("Nilesh", (k, v) -> k.length() + v);
System.out.println("v1: " + v1);
System.out.println(conMap1);
System.out.println("--- Example-2 ---");
ConcurrentHashMap<Integer, String> conMap2 = new ConcurrentHashMap<>();
conMap2.put(10, "Varanasi");
conMap2.put(20, "Prayag");
String v2 = conMap2.compute(10, (k, v) -> v + "-" + k * 2);
System.out.println("v2: " + v2);
System.out.println(conMap2);
}
}
--- Example-1 ---
v1: 31
{Mahesh=22, Nilesh=31}
--- Example-2 ---
v2: Varanasi-20
{20=Prayag, 10=Varanasi-20}
