TreeMap merge(K, V, BiFunction) in Java

merge(K, V, BiFunction): This method is available in java.util.TreeMap class of Java.

Syntax:

String java.util.TreeMap.merge(K key, V value, BiFunction<? super V, ? super V, ? extends V> remappingFunction)

This method takes three arguments. If the specified key is not already associated with a value or is associated with null, associate it with the given non-null value. Otherwise, replaces the associated value with the results of the given remapping function, or removes if the result is null.

Parameters: Three parameters are required for this method.

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

value: the non-null value to be merged with the existing value associated with the key or if no existing value or a null value is associated with the key, to be associated with the key.

remappingFunction: the remapping function to recompute a value if present.

Returns: the new value associated with the specified key, or null if no value is associated with the key.

Throws:

ConcurrentModificationException - if it is detected that the remapping function modified this map

Approach

Java

import java.util.TreeMap;
import java.util.function.BiFunction;

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

        TreeMap<Integer, String> treeMap = 
             new TreeMap<Integer, String>();

        treeMap.put(2, "Hello");
        treeMap.put(11, "Java");
        treeMap.put(23, "Program");
        treeMap.put(6, "C++");
        treeMap.put(25, "Program");

        Integer key = 2;

        String value = " World";

        BiFunction<? super String, ? super String, 
        ? extends String> remappingFunction = (a, b) -> a + b;

        System.out.println(treeMap.merge(key, 
                       value, remappingFunction));

    }
}

Output:

Hello World