Java Collection removeAll() Method

The removeAll() method of Java Collection Interface only removes those elements of the Collection that are contained in the specified collection.

Syntax

Parameters

Here, the parameter 'c' represents the collection which contains the elements to be removed from the invoked collection.

Return Value:

The removeAll () method returns a Boolean value 'true' if the collection has changed as a result of the call, else it returns 'false'.

Throws:

UnsupportedOperationException- if the removeAll method is not supported by this collection.

ClassCastException- if the types of one or more elements in this collection are not compatible with the invoked collection.

NullPointerException- if this collection is null or it contains one or more null elements and this collection does not allow null elements.

Example 1

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.ConcurrentLinkedQueue;
public class JavaCollectionRemoveAllExample1 {
    public static void main(String[] args) {
        Collection<Character> collection = new ConcurrentLinkedQueue<Character>();
        char i;
        for(i='1';i<='9';++i){
            collection.add(i);
        }
        System.out.println("collection : "+collection);
        List<Character> list = new ArrayList<Character>();
        list.add('2');
        list.add('4');
        list.add('6');
        list.add('8');
        System.out.println("List of even numbers : "+list);
        //removes all the elements in the collection which are present in list
        collection.removeAll(list);
        System.out.println("Odd numbers : "+collection);
    }
}

Test it Now

Output:

collection : [1, 2, 3, 4, 5, 6, 7, 8, 9]
List of even numbers : [2, 4, 6, 8]
Odd numbers : [1, 3, 5, 7, 9]

Example 2

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.ConcurrentLinkedQueue;
public class JavaCollectionRemoveAllExample2 {
    public static void main(String[] args) {
        Collection<Integer> collection = new ConcurrentLinkedQueue<Integer>();
        List<Integer> list = new ArrayList<Integer>();
        for (int i=1;i<21;i++){
            collection.add(i);}
        System.out.println("Total no : "+ collection);
        for (int i=1;i<21;i++) {
            int j=i%2;
            
            if (j != 0) {
                list.add(i);
            }
        }
        //removes all the elements int the collection which are present in list
        collection.removeAll(list);
        System.out.println(" Table of 2 : "+collection);
    }
}

Test it Now

Output:

Total no : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
 Table of 2 : [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

Example 3

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.ConcurrentLinkedQueue;
public class JavaCollectionRemoveAllExample3 {
    public static void main(String[] args) {
        Collection<Character> collection = new ConcurrentLinkedQueue<Character>();
        char c;
        for(c='1';c<='9';++c){
            // collection does not support null elements
            collection.add(null);
        }
        System.out.println("collection : "+collection);
        List<Character> list = new ArrayList<Character>();
        list.add('2');
        list.add(null);
        list.add('6');
        list.add('8');
        System.out.println("List of even numbers : "+list);
        //removes all the elements in the collection which are present in list
        collection.removeAll(list);
        System.out.println("Odd numbers : "+collection);
    }
}

Test it Now

Output:

Exception in thread "main" java.lang.NullPointerException
	at java.util.concurrent.ConcurrentLinkedQueue.checkNotNull(ConcurrentLinkedQueue.java:920)
	at java.util.concurrent.ConcurrentLinkedQueue.offer(ConcurrentLinkedQueue.java:327)
	at java.util.concurrent.ConcurrentLinkedQueue.add(ConcurrentLinkedQueue.java:297)
	at com.javaTpoint.JavaCollectionRemoveAllExample3.main(JavaCollectionRemoveAllExample3.java:13)

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