Java – Remove Key-Value from HashMap using remove()

Java HashMap.remove()

In this tutorial, we will learn about the Java HashMap.remove() function, and learn how to use this function to remove a key-value mapping from this HashMap, with the help of examples.

remove()

HashMap.remove() removes the mapping for the specified key from this map, if present, and returns the previously associated value for this key.

If the key is not already present, remove() returns null.

The syntax of remove() function is

remove(key)

where

Parameter	Type	Description
key	Object	The key for which we would like to remove the mapping in this HashMap.

Returns

The function returns the value associated with the key.

Examples

1. remove(key) basic example

In this example, we will initialize a HashMap hashMap with some mappings in it. We will remove the key-value mapping for the key 3 in this HashMap using remove() method. Since, the key 3 is present in this HashMap, remove() returns the value corresponding to this key.

Java Program

import java.util.HashMap;

public class Example{ 
	public static void main(String[] args) {
		HashMap<Integer, String> hashMap = new HashMap<>();
		hashMap.put(1, "A");
		hashMap.put(2, "B");
		hashMap.put(3, "C");
		hashMap.put(4, "D");
		System.out.println("HashMap before remove : " + hashMap);
		
		int key = 3;
		String value = hashMap.remove(key);
		System.out.println("HashMap after  remove : " + hashMap);
		System.out.println("remove() returned value : " + value);
	}
}

Output

HashMap before remove : {1=A, 2=B, 3=C, 4=D}
HashMap after  remove : {1=A, 2=B, 4=D}
remove() returned value : C

2. remove(key) when key is not present in HashMap

In this example, we will initialize a HashMap hashMap with some mappings in it. We will remove the key-value mapping for the key 5 in this HashMap using remove() method. Since, the key 5 is not present in this HashMap, remove() does nothing to this HashMap and returns null value.

Java Program

import java.util.HashMap;

public class Example{ 
	public static void main(String[] args) {
		HashMap<Integer, String> hashMap = new HashMap<>();
		hashMap.put(1, "A");
		hashMap.put(2, "B");
		hashMap.put(3, "C");
		hashMap.put(4, "D");
		System.out.println("HashMap before remove : " + hashMap);
		
		int key = 5;
		String value = hashMap.remove(key);
		System.out.println("HashMap after  remove : " + hashMap);
		System.out.println("remove() returned value : " + value);
	}
}

Output

HashMap before remove : {1=A, 2=B, 3=C, 4=D}
HashMap after  remove : {1=A, 2=B, 3=C, 4=D}
remove() returned value : null

Conclusion

In this Java Tutorial, we have learnt the syntax of Java HashMap.remove() function, and also learnt how to use this function with the help of examples.