AbstractSequentialList retainAll() method in Java with Example

The retainAll() method of java.util.AbstractSequentialList class is used to retain from this list all of its elements that are contained in the specified collection. Syntax:

public boolean retainAll(Collection c)

Parameters: This method takes collection c as a parameter containing elements to be retained from this list. Returns Value: This method returns true if this list changed as a result of the call. Exception: This method throws NullPointerException if this list contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null. Below are the examples to illustrate the retainAll() method. Example 1:

Java

// Java program to demonstrate
// retainAll() method for Integer value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv) throws Exception
    {

        try {

            // Creating object of AbstractSequentialList<Integer>
            AbstractSequentialList<Integer>
                arrlist1 = new LinkedList<Integer>();

            // Populating arrlist1
            arrlist1.add(1);
            arrlist1.add(2);
            arrlist1.add(3);
            arrlist1.add(4);
            arrlist1.add(5);

            // print arrlist1
            System.out.println("AbstractSequentialList before "
                               + "retainAll() operation : "
                               + arrlist1);

            // Creating another object of  AbstractSequentialList<Integer>
            AbstractSequentialList<Integer>
                arrlist2 = new LinkedList<Integer>();
            arrlist2.add(1);
            arrlist2.add(2);
            arrlist2.add(3);

            // print arrlist2
            System.out.println("Collection Elements"
                               + " to be retained : "
                               + arrlist2);

            // Removing elements from arrlist
            // specified in arrlist2
            // using retainAll() method
            arrlist1.retainAll(arrlist2);

            // print arrlist1
            System.out.println("AbstractSequentialList after "
                               + "retainAll() operation : "
                               + arrlist1);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

AbstractSequentialList before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : [1, 2, 3]
AbstractSequentialList after retainAll() operation : [1, 2, 3]

Example 2: For NullPointerException

Java

// Java program to demonstrate
// retainAll() method for Integer value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv) throws Exception
    {

        try {

            // Creating object of AbstractSequentialList<Integer>
            AbstractSequentialList<Integer>
                arrlist1 = new LinkedList<Integer>();

            // Populating arrlist1
            arrlist1.add(1);
            arrlist1.add(2);
            arrlist1.add(3);
            arrlist1.add(4);
            arrlist1.add(5);

            // print arrlist1
            System.out.println("AbstractSequentialList before "
                               + "retainAll() operation : "
                               + arrlist1);

            // Creating another object of  AbstractSequentialList<Integer>
            AbstractSequentialList<Integer>
                arrlist2 = null;

            // print arrlist2
            System.out.println("Collection Elements"
                               + " to be retained : "
                               + arrlist2);

            System.out.println("\nTrying to pass "
                               + "null as a specified element\n");

            // Removing elements from arrlist
            // specified in arrlist2
            // using retainAll() method
            arrlist1.retainAll(arrlist2);

            // print arrlist1
            System.out.println("AbstractSequentialList after "
                               + "retainAll() operation : "
                               + arrlist1);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

AbstractSequentialList before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : null

Trying to pass null as a specified element

Exception thrown : java.lang.NullPointerException