The replace(K key, V value) method of Map interface, implemented by HashMap class is used to replace the value of the specified key only if the key is previously mapped with some value.
Syntax:
public V replace(K key, V value)
Parameters: This method accepts two parameters:
- key: which is the key of the element whose value has to be replaced.
- value: which is the new value which has to be mapped with the provided key.
Return Value: This method returns the previous value associated with the specified key. If there is no such key mapped, then it returns null, if the implementation supports null value.
Exceptions: This method will throw:
- NullPointerException if the specified key or value is null, and this map does not permit null keys or values and
- IllegalArgumentException if some property of the specified key or value prevents it from being stored in this map.
Program 1:
// Java program to demonstrate// replace(K key, V value) method import java.util.*; public class GFG { // Main method public static void main(String[] args) { // Create a HashMap and add some values HashMap<String, Integer> map = new HashMap<>(); map.put("a", 100); map.put("b", 300); map.put("c", 300); map.put("d", 400); // print map details System.out.println("HashMap: " + map.toString()); // provide value for the key which has // to replace it's current value, // using replace(K key, V value) method map.replace("b", 200); // print new mapping System.out.println("New HashMap: " + map.toString()); }} |
Output:
HashMap: {a=100, b=300, c=300, d=400}
New HashMap: {a=100, b=200, c=300, d=400}
Program 2:
// Java program to demonstrate// replace(K key, V value) method import java.util.*; public class GFG { // Main method public static void main(String[] args) { // Create a HashMap and add some values HashMap<String, Integer> map = new HashMap<>(); map.put("a", 100); map.put("b", 300); map.put("c", 300); map.put("d", 400); // print map details System.out.println("HashMap: " + map.toString()); // provide value for the key which has // to replace it's current value, and will // store the value in k using the // replace(K key, V value) method int k = map.replace("b", 200); // print the value of k System.out.println("Previous value of 'b': " + k); // print new mapping System.out.println("New HashMap: " + map.toString()); }} |
Output:
HashMap: {a=100, b=300, c=300, d=400}
Previous value of 'b': 300
New HashMap: {a=100, b=200, c=300, d=400}
Program 3:
// Java program to demonstrate// replace(K key, V value) method import java.util.*; public class GFG { // Main method public static void main(String[] args) { // Create a HashMap and add some values HashMap<String, Integer> map = new HashMap<>(); map.put("a", 100); map.put("b", 300); map.put("c", 300); map.put("d", 400); // print map details System.out.println("HashMap: " + map.toString()); // provide value for the key which is // not mapped previously and store the // return value in Integer k, using // replace(K key, V value) method Integer k = map.replace("e", 200); // print the value of k System.out.println("Value of k, returned " + "for key 'e': " + k); // print new mapping System.out.println("New HashMap: " + map.toString()); }} |
Output:
HashMap: {a=100, b=300, c=300, d=400}
Value of k, returned for key 'e': null
New HashMap: {a=100, b=300, c=300, d=400}
References: https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html#replace-K-V-
