The removeAll() method in CopyOnWriteArrayList class that removes all the elements that are contained in the specified collection from the CopyOnArrayList object you call on.
Syntax:
public boolean removeAll(Collection collection)
Parameter: The method accepts only a single parameter collection which is to be removed from the calling object.
Return Value: This method returns a boolean value. It returns true if this remove operation is successful.
Exception: This method throws following exceptions:
- ClassCastException: if the class of an element of this list is incompatible with the specified collection.
- NullPointerException: if the specified collection is null or if this list contains a null element and the specified collection does not permit null elements.
Below examples illustrates the removeAll() method:
Example 1:
// Java program to demonstrate removeAll() method  import java.util.ArrayList;import java.util.concurrent.CopyOnWriteArrayList;  public class Demo {      public static void main(String args[])    {          // Get the CopyOnWriteArrayList        CopyOnWriteArrayList<String> wishlist            = new CopyOnWriteArrayList<>();          // Add the elements in the CopyOnWriteArrayList        wishlist.add("TV");        wishlist.add("computer");        wishlist.add("play station");        wishlist.add("mobile");        wishlist.add("smart watch");          // Print the CopyOnWriteArrayList        System.out.println("CopyOnWriteArrayList: \n"                           + wishlist);          // Get the collection to be removed        ArrayList<String> checkList            = new ArrayList<>();          checkList.add("play station");        checkList.add("TV");        checkList.add("mobile");          System.out.println("\nCollection to be removed:\n"                           + checkList);          // Remove the collection from CopyOnWriteArrayList        // using removeAll() method        wishlist.removeAll(checkList);          // Print the CopyOnWriteArrayList after removal        System.out.println("\nAfter removal of collection"                           + " from CopyOnWriteArrayList:\n"                           + wishlist);    }} |
Output:
CopyOnWriteArrayList: [TV, computer, play station, mobile, smart watch] Collection to be removed: [play station, TV, mobile] After removal of collection from CopyOnWriteArrayList: [computer, smart watch]
Example 2: To show NullPointerException
// Java program to demonstrate removeAll() method  import java.util.ArrayList;import java.util.concurrent.CopyOnWriteArrayList;  public class Demo {      public static void main(String args[])    {          // Get the CopyOnWriteArrayList        CopyOnWriteArrayList<String> wishlist            = new CopyOnWriteArrayList<>();          // Add the elements in the CopyOnWriteArrayList        wishlist.add("TV");        wishlist.add("computer");        wishlist.add("play station");        wishlist.add("mobile");        wishlist.add("smart watch");          // Print the CopyOnWriteArrayList        System.out.println("CopyOnWriteArrayList: \n"                           + wishlist);          // Get the collection to be removed        ArrayList<String> checkList            = null;        System.out.println("\nCollection to be removed: "                           + checkList);          try {              // Remove the collection from CopyOnWriteArrayList            // using removeAll() method            wishlist.removeAll(checkList);        }        catch (Exception e) {              // Print the Exception            System.out.println("\nException thrown"                               + " while removing null "                               + "from the CopyOnWriteArrayList: \n"                               + e);        }    }} |
Output:
CopyOnWriteArrayList: [TV, computer, play station, mobile, smart watch] Collection to be removed: null Exception thrown while removing null from the CopyOnWriteArrayList: java.lang.NullPointerException
