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() methodimport 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("geeks");        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("geeks");        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: [geeks, shaan, gfg, programming] CopyOnWriteArrayList2: [geeks, gfg, qwe] After applying retainAll() method on ArrLis2 CopyOnWriteArrayList1: [geeks, shaan, gfg, programming] CopyOnWriteArrayList2: [geeks, gfg]
