Java LinkedHashMap clear() Method

The clear() method in Java is a built-in method of the java.util.LinkedHashMap class. This method is used to remove all the key-value mappings from a LinkedHashMap. After invoking this method, the map becomes empty.

This method is very helpful when we want to reuse an existing map object without creating a new one.

Syntax of clear() Method

public void clear()

• Parameters: This method does not accept any parameters.
• Return Value: This method does not return any value i.e., its return type is void.

Examples of Java LinkedHashMap clear() Method

Example 1: In this example, we are going to create a LinkedHashMap with integer keys and string values, then we will use the clear() method to remove all entries.

// Java program to demonstrate 
// clear() on LinkedHashMap with Integer keys
import java.util.LinkedHashMap;

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

        // Create a LinkedHashMap with Integer keys
        LinkedHashMap<Integer, String> m = new LinkedHashMap<>();

        // Add entries to the map
        m.put(10, "Geeks");
        m.put(15, "4");
        m.put(20, "Geeks");
        m.put(25, "Welcomes");
        m.put(30, "You");

        System.out.println("Initial Mappings are: " + m);

        // Clear all entries from the map
        m.clear();

        System.out.println("After clear(): " + m);
    }
}

Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
After clear(): {}

Explanation: Here, all entries were removed from the LinkedHashMap using clear() method.

Example 2: In this example, we will map the Integer values to string keys using the clear() method. It also shows how duplicate keys behave.

// Java program to demonstrate 
// clear() on LinkedHashMap with String keys
import java.util.LinkedHashMap;

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

        // Create a LinkedHashMap with String keys
        LinkedHashMap<String, Integer> m = new LinkedHashMap<>();

        // Add entries to the map
        m.put("Geeks", 10);
        m.put("4", 15);
        
        // Overwrites previous key
        m.put("Geeks", 20); 
        m.put("Welcomes", 25);
        m.put("You", 30);

        System.out.println("Initial Mappings are: " + m);

        // Clear all entries from the map
        m.clear();

        System.out.println("After clear(): " + m);
    }
}

Initial Mappings are: {Geeks=20, 4=15, Welcomes=25, You=30}
After clear(): {}

Explanation: Here, the duplicate key "Geeks" was updated before clearing. And after calling the clear() method, all entries were removed and the map became an empty map.

Important Points:

• The clear() method deletes all mappings from the LinkedHashMap.
• It does not delete the map object itself, it only deletes its contents.
• It is a void method and does not throw any exceptions.
• This method is very useful for resetting the map state without creating a new instance.

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Article Tags :

• Java
• Java-Collections
• Java - util package
• Java-LinkedHashMap

Practice Tags :

• Java
• Java-Collections