WeakHashMap compute(K, BiFunction) in Java

compute(K, BiFunction): This method is available in java.util.WeakHashMap class of Java.

Syntax:

Integer java.util.Map.compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)

This method takes one argument. This method attempts to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping).

Parameters: Two parameters are required for this method.

key: key with which the specified value is to be associated.

remappingFunction: the remapping function to compute a value.

Returns: the new value associated with the specified key, or null if none.

Throws:

1. NullPointerException - if the specified key is null and this map does not support null keys, or the remappingFunction is null.

2. UnsupportedOperationException - if the put operation is not supported by this map.

3. ClassCastException - if the class of the specified key or value prevents it from being stored in this map.

4. IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map.

Approach 1: When no exception

Java

import java.util.WeakHashMap;
import java.util.function.BiFunction;

public class WeakHashMapcompute {
    public static void main(String[] args) {

        WeakHashMap<String, Integer> weakHashMap = 
                   new WeakHashMap<String, Integer>();

        weakHashMap.put("Java", 1);
        weakHashMap.put("Hello", 2);

        String key = "Hello";
        BiFunction<? super String, ? super Integer, ? 
        extends Integer> remappingFunction = (k, v) -> v;
        System.out.println(weakHashMap.compute(key,
                                    remappingFunction));
    }
}

Output:

2

Approach 2: NullPointerException 

Java

import java.util.WeakHashMap;
import java.util.function.BiFunction;

public class WeakHashMapcompute {
    public static void main(String[] args) {

        WeakHashMap<String, Integer> weakHashMap = 
                 new WeakHashMap<String, Integer>();

        weakHashMap.put("Java", 1);
        weakHashMap.put("Hello", 2);

        String key = "Hello";
        BiFunction<? super String, ? super Integer, 
            ? extends Integer> remappingFunction = null;
        System.out.println(weakHashMap.compute(key, 
                             remappingFunction));
    }
}

Output:

Exception in thread "main" java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:208)
	at java.base/java.util.Map.compute(Map.java:1167)