Java Collection clear() Method

The clear() method of Java Collection Interface removes all of the elements from this collection. It returns a Boolean value 'true', if it successfully empties the collection.

Syntax

Parameters

Throws

UnsupportedOperationException- if the clear operation is not supported by this collection.

Example 1

import java.util.Collection;
import java.util.concurrent.LinkedBlockingDeque;
public class JavaCollectionClearExample1 {
    public static void main(String[] args) {
        Collection<Integer> collection = new LinkedBlockingDeque<Integer>();
        collection.add(23);
        collection.add(123);
        collection.add(56);
        System.out.println("Collection : "+collection);
        System.out.println("After applying clear() method :  ");
        // clear() method will erase the whole collection
        collection.clear();
        System.out.println("Collection : "+collection);
    }
}

Test it Now

Output:

Collection : [23, 123, 56]
After applying clear() method :  
Collection : []

Example 2

import java.util.Collection;
import java.util.Scanner;
import java.util.concurrent.LinkedBlockingDeque;
class ShoppingList{
    int SNo;
    String Name;
    public ShoppingList(int SNo, String name) { 
        this.SNo = SNo;
        Name = name;
    }
    public String toString(){
        return SNo+". "+ Name ;
    }
}
public class JavaCollectionClearExample2 {
    public static void main(String[] args) {
        Collection<ShoppingList> collection = new LinkedBlockingDeque<ShoppingList>();
        ShoppingList list1 = new ShoppingList(1,"Sugar");
        ShoppingList list2= new ShoppingList(2,"Salt");
        ShoppingList list3 = new ShoppingList(3,"Potato");
        ShoppingList list4 = new ShoppingList(4,"Rice");
        collection.add(list1);
        collection.add(list2);
        collection.add(list3);
        collection.add(list4);
        for (ShoppingList xyz : collection ){
            System.out.println(xyz);
        }
        Scanner scanner = new Scanner(System.in);
        System.out.println("Is Your shopping done.?");
        System.out.print("true/false : ");
        Boolean val = scanner.nextBoolean();
        if(val.equals(true)){
            // clear() method will erase the whole deque
            collection.clear();
            System.out.println("Your queue has been emptied successfully.");
        }
        else{
            System.out.println("Ok .You can add more items to your list");
        }
    }
}

Output:

1. Sugar
2. Salt
3. Potato
4. Rice
Is Your shopping done.?
true/false : true
Your queue has been emptied successfully.

Process finished with exit code 0

Example 3

import java.util.Collection;
import java.util.concurrent.LinkedBlockingDeque;
public class JavaCollectionClearExample3 {
    public static void main(String[] args) {
        Collection<Integer> collection = new LinkedBlockingDeque<Integer>();
        collection.add(23);
        collection.add(null);
        collection.add(56);
        System.out.println("Collection : "+collection);
        System.out.println("After applying clear() method :  ");
        // clear() method will erase the whole collection
        collection.clear();
        System.out.println("Collection : "+collection);
    }
}

Test it Now

Output:

Exception in thread "main" java.lang.NullPointerException
	at java.util.concurrent.LinkedBlockingDeque.offerLast(LinkedBlockingDeque.java:357)
	at java.util.concurrent.LinkedBlockingDeque.addLast(LinkedBlockingDeque.java:334)
	at java.util.concurrent.LinkedBlockingDeque.add(LinkedBlockingDeque.java:633)
	at com.javaTpoint.JavaCollectionClearExample3.main(JavaCollectionClearExample3.java:9)

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