AbstractSequentialList retainAll() method in Java with Example

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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