Java HashMap replace(key, oldValue, newValue) Method
Last Updated : 22 Jan, 2025
The replace(key, oldValue, newValue) method of the HashMap class in Java is used to conditionally replace the value of a specified key if, and only if, the current value matches the specified old value.
Example 1: This example demonstrates replacing a value only if the key is mapped to the given old value.
Java // Java program demonstrates the working of replace() import java.util.HashMap; public class Geeks { public static void main(String[] args) { // Create a HashMap HashMap<Integer, String> hm = new HashMap<>(); hm.put(1, "Geek1"); hm.put(2, "Geek2"); hm.put(3, "Geek3"); System.out.println("Original map: " + hm); // Replace value for key 2 only // if the current value is "Geek2" boolean b = hm.replace(2, "Geek2", "Geek10"); System.out.println("Was value replaced? " + b); System.out.println("Updated map: " + hm); } } OutputOriginal map: {1=Geek1, 2=Geek2, 3=Geek3} Was value replaced? true Updated map: {1=Geek1, 2=Geek10, 3=Geek3} Syntax of replace(key, oldValue, newValue) Method
boolean replace(K key, V oldValue, V newValue)
Parameters:
- key: The key whose associated value is to be replaced.
- oldValue: The expected current value associated with the key.
- newValue: The new value to associated with the key.
Return Type:
This method returns "true" if the value associated with the key is replaced successfully or return "false" if the key does not exist in the map.
Exception:
- NullPointerException occurs only if null is used for a key or value in a map that doesn't support null.
- IllegalArgumentException only applies to certain Map implementations (like some custom implementations or ConcurrentHashMap).
Example 2: This example shows what happens when the old value provided does not match the current value.
Java // Java program demonstrates mismatched old value import java.util.HashMap; public class Geeks { public static void main(String[] args) { // Create a HashMap HashMap<Integer, String> hm = new HashMap<>(); hm.put(1, "Java"); hm.put(2, "C++"); hm.put(3, "Python"); System.out.println("Initial HashMap: " + hm); // Replace value for key 2 // if old value matches boolean b = hm.replace(2, "JavaScript", "C#"); System.out.println("Was replacement successful? " + b); System.out.println("Updated HashMap: " + hm); } } OutputInitial HashMap: {1=Java, 2=C++, 3=Python} Was replacement successful? false Updated HashMap: {1=Java, 2=C++, 3=Python}
Example 3: This example demonstrates that if the key does not exists, the method returns false.
Java // Java program demonstrates what happens // if the key does not exists import java.util.HashMap; public class Geeks { public static void main(String[] args) { // Create a HashMap HashMap<Integer, String> hm = new HashMap<>(); hm.put(1, "Java"); hm.put(2, "C++"); System.out.println("Initial HashMap: " + hm); // Replace value for key 2 // if old value matches boolean b = hm.replace(3, "JavaScript", "C#"); System.out.println("Was replacement successful? " + b); System.out.println("Updated HashMap: " + hm); } } OutputInitial HashMap: {1=Java, 2=C++} Was replacement successful? false Updated HashMap: {1=Java, 2=C++}