Map remove() Method in Java with Examples

The map.remove() method is used to remove the mapping for a key from this map if it is present in the map. 

Syntax:  

V remove(Object key)

• Parameters: This method has the only argument key, whose mapping is to be removed from the map.
• Returns: This method returns the value to which this map previously associated the key, or null if the map contained no mapping for the key.
• Time Complexity: Average time complexity of O(1) and a worst-case time complexity of O(n).

Map remove() Method in Java

Example 1: The below programs show the implementation of the map.remove() method.

// Java code to show the implementation of
// remove method in Map interface
import java.util.*;
public class GfG {

    // Driver code
    public static void main(String[] args)
    {

        // Initializing a Map of type HashMap
        Map<Integer, String> map = new HashMap<>();
        map.put(1, "One");
        map.put(3, "Three");
        map.put(5, "Five");
        map.put(7, "Seven");
        map.put(9, "Nine");
        System.out.println(map);

        map.remove(3);

        System.out.println(map);

        // If it doesn't exists, returns
        // null and does not affects the map
        map.remove(2);

        System.out.println(map);
    }
}

{1=One, 3=Three, 5=Five, 7=Seven, 9=Nine}
{1=One, 5=Five, 7=Seven, 9=Nine}
{1=One, 5=Five, 7=Seven, 9=Nine}

Explanation of the Program:

• This example demonstrates the use of the remove method in the Map interface using a HashMap.
• It initializes a HashMap with integer keys and string values, then removes the entry with key 3, and attempts to remove a non-existent key 2.
• The output shows the map before and after the removals, illustrating how the remove method works and that attempting to remove a non-existent key has no effect on the map.

Example 2: Below is the code to show implementation of put(). 

// Java code to show the implementation of
// remove method in Map interface
import java.util.*;
public class GfG {

    // Driver code
    public static void main(String[] args)
    {

        // Initializing a Map of type HashMap
        Map<String, String> map = new HashMap<>();
        map.put("1", "One");
        map.put("3", "Three");
        map.put("5", "Five");
        map.put("7", "Seven");
        map.put("9", "Nine");
        System.out.println(map);

        map.remove("3");

        System.out.println(map);
    }
}

{1=One, 3=Three, 5=Five, 7=Seven, 9=Nine}
{1=One, 5=Five, 7=Seven, 9=Nine}

Explanation of the Program:

• This program demonstrates the use of the remove method in the Map interface using a HashMap.
• It also initializes a HashMap with string keys and values, prints the map, removes the entry with key "3", and then prints the map again to show the result of the removal.
• The output illustrates how the remove method affects the map by removing the specified key-value pair.