CopyOnWriteArrayList retainAll() method in Java with Examples ❤️

The Java.util.concurrent.CopyOnArrayList.retainAll() method in Java is used to retain only the elements in the list that are contained in specific collection.

Syntax:

 public boolean retainAll(Collection col)

Parameters: This method accepts a mandatory parameter col which is of the type of collection. This is the collection of elements to be retained in this vector.

Return Type: This method returns a boolean value true if the list is changed at all as a result of call else false.

Exception: This method throws a NullPointerException if the specified collection is NULL.

Below Programs illustrate the retainAll() method of CopyOnArrayList in Java:

Program 1: This program involves CopyOnArraylist retainAll() method of Integer Type:

// Java Program to illustrate CopyOnArrayList 
// retainAll() method 
import java.util.concurrent.CopyOnWriteArrayList; 
import java.util.*; 
  
public class GFG { 
    public static void main(String[] args) 
    { 
        // create object of CopyOnWriteArrayList 
        CopyOnWriteArrayList<Integer> ArrLis1 
            = new CopyOnWriteArrayList<Integer>(); 
  
        // Add elements 
        ArrLis1.add(34); 
        ArrLis1.add(66); 
        ArrLis1.add(72); 
        ArrLis1.add(10); 
  
        // print CopyOnWriteArrayList 
        System.out.println("CopyOnWriteArrayList1: "
                           + ArrLis1); 
  
        // create object of CopyOnWriteArrayList 
        CopyOnWriteArrayList<Integer> ArrLis2 
            = new CopyOnWriteArrayList<Integer>(); 
  
        // Add elements 
        ArrLis2.add(10); 
        ArrLis2.add(66); 
        ArrLis2.add(97); 
  
        // print CopyOnWriteArrayList 
        System.out.println("CopyOnWriteArrayList2: "
                           + ArrLis2); 
  
        // Applying the function 
        ArrLis2.retainAll(ArrLis1); 
  
        // print CopyOnWriteArrayLists 
  
        System.out.println("After applying retainAll()"
                           + " method on ArrLis2"); 
        System.out.println("CopyOnWriteArrayList1: "
                           + ArrLis1); 
        System.out.println("CopyOnWriteArrayList2: "
                           + ArrLis2); 
    } 
} 

Output:

CopyOnWriteArrayList1: [34, 66, 72, 10]
CopyOnWriteArrayList2: [10, 66, 97]
After applying retainAll() method on ArrLis2
CopyOnWriteArrayList1: [34, 66, 72, 10]
CopyOnWriteArrayList2: [10, 66]

Program 2: This program involves CopyOnArraylist retainAll() method of String Type:

// Java Program to illustrate CopyOnArrayList 
// retainAll() method 
  
import java.util.concurrent.CopyOnWriteArrayList; 
import java.util.*; 
  
public class GFG { 
    public static void main(String[] args) 
    { 
        CopyOnWriteArrayList<String> ArrLis1 
            = new CopyOnWriteArrayList<String>(); 
  
        // Add elements 
        ArrLis1.add("Beginner"); 
        ArrLis1.add("shaan"); 
        ArrLis1.add("gfg"); 
        ArrLis1.add("programming"); 
  
        // print CopyOnWriteArrayList 
        System.out.println("CopyOnWriteArrayList1: "
                           + ArrLis1); 
  
        // create object of CopyOnWriteArrayList 
        CopyOnWriteArrayList<String> ArrLis2 
            = new CopyOnWriteArrayList<String>(); 
  
        // Add elements 
        ArrLis2.add("Beginner"); 
        ArrLis2.add("gfg"); 
        ArrLis2.add("qwe"); 
  
        // print CopyOnWriteArrayList 
        System.out.println("CopyOnWriteArrayList2: "
                           + ArrLis2); 
  
        // Applying the function 
        ArrLis2.retainAll(ArrLis1); 
  
        // print CopyOnWriteArrayLists 
  
        System.out.println("After applying retainAll()"
                           + " method on ArrLis2"); 
        System.out.println("CopyOnWriteArrayList1: "
                           + ArrLis1); 
        System.out.println("CopyOnWriteArrayList2: "
                           + ArrLis2); 
    } 
} 

Output:

CopyOnWriteArrayList1: [Beginner, shaan, gfg, programming]
CopyOnWriteArrayList2: [Beginner, gfg, qwe]
After applying retainAll() method on ArrLis2
CopyOnWriteArrayList1: [Beginner, shaan, gfg, programming]
CopyOnWriteArrayList2: [Beginner, gfg]

CopyOnWriteArrayList retainAll() method in Java with Examples

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