ArrayList removeAll() method
In this tutorial, we will see the removeAll(Collection c) method of the ArrayList class in Java. This method removes from this list all of its elements that are contained in the specified collection.
Introduction
ArrayList is a widely used class to store and retrieve data in a collection framework.
We have seen how to remove elements from the ArrayList. Today, we will see how to remove all the elements from ArrayList specified in another collection.
Previously, we have seen a few methods of the ArrayList class before like add(), addAll(), remove(), set(), iterate(), clear(), contains(), get(), removeRange(), retainAll(), trimToSize(), indexOf(), lastIndexOf() and removeIf() method.
Today we will see the ` removeAll(Collection c)` method.
ArrayList ` removeAll(Collection c)` method
The ` removeAll(Collection c)` method removes from this list all of its elements that are contained in the specified collection.
The method signature is given below
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public boolean removeAll(Collection<?> c)
As shown in the method signature, this method accepts only one parameter i.e. Collection c.
This method returns a boolean value. This method returns true if the ArrayList got changed as a method call. Otherwise, it returns false.
Let’s see an example Java program for the ArrayList removeAll() method.
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import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;
/**
* A Java program showing an example for the removeAll()
* method of the ArrayList class in Java.
*
* @author coderolls.com
*/
public class ArrayListRemoveAllExample {
public static void main(String[] args) {
// create an empty ArrayList object 'states'
List<String> states = new ArrayList<String>();
// add state in the ArrayList, Florida multiple times
states.add("California");
states.add("Texas");
states.add("Montana");
states.add("Arizona");
states.add("Florida");
states.add("Michigan");
states.add("New Jersey");
states.add("Washington");
states.add("Ohio");
states.add("Minnesota");
states.add("Colorado");
states.add("Missouri");
states.add("Nevada");
//Create another ArrayList for items to be removed
List<String> statesToBeRemoved = new ArrayList<String>();
statesToBeRemoved.add("Minnesota");
statesToBeRemoved.add("Missouri");
statesToBeRemoved.add("Montana");
statesToBeRemoved.add("Michigan");
System.out.println("The states list before the removeAll() method call: \n" + states);
// removes all elements specified in the ArrayList statesToBeRemoved
states.removeAll(statesToBeRemoved);
System.out.println("\nThe states list after the removeAll() method call: \n" + states);
}
}
Output:
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The states list before the removeAll() method call:
[California, Texas, Montana, Arizona, Florida, Michigan, New Jersey, Washington, Ohio, Minnesota, Colorado, Missouri, Nevada]
The states list after the removeAll() method call:
[California, Texas, Arizona, Florida, New Jersey, Washington, Ohio, Colorado, Nevada]
Exceptions
We can get the following exceptions while invoking the removeAll(Collection c) method
ClassCastExceptionNullPointerException
ClassCastException
If the class of an element of this list is incompatible with the specified collection, we can get the ClassCastException. This is an option restriction. (Read more about optional)
NullPointerException
If this list contains a null element and the specified collection does not permit null elements, we can get the NullPointerException. This is an option restriction. (Read more about optional).
Or if the specified collection is null, we will surely get the NullPointerException.
Let’s see an example Java program to show the case of NullPointerException while invoking the removeAll() method.
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import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;
/**
* A Java program showing a NullPointerException case
* for the removeAll() method of the ArrayList class in Java.
*
* @author coderolls.com
*/
public class ArrayListRemoveAllNullPointerException {
public static void main(String[] args) {
// create an empty ArrayList object 'states'
List<String> states = new ArrayList<String>();
// add state in the ArrayList, Florida multiple times
states.add("California");
states.add("Texas");
states.add("Montana");
states.add("Arizona");
states.add("Florida");
states.add("Michigan");
states.add("New Jersey");
states.add("Washington");
states.add("Ohio");
states.add("Minnesota");
states.add("Colorado");
states.add("Missouri");
states.add("Nevada");
//Create another ArrayList with a null value,
//so that removeAll will throw NullPointerException
List<String> statesToBeRemoved =null;
System.out.println("The states list before the removeAll() method call: \n" + states);
// removes all elements specified in the ArrayList statesToBeRemoved
states.removeAll(statesToBeRemoved);
System.out.println("\nThe states list after the removeAll() method call: \n" + states);
}
}
Output:
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The states list before the removeAll() method call:
[California, Texas, Montana, Arizona, Florida, Michigan, New Jersey, Washington, Ohio, Minnesota, Colorado, Missouri, Nevada]
Exception in thread "main" java.lang.NullPointerException
at java.util.Objects.requireNonNull(Objects.java:203)
at java.util.ArrayList.removeAll(ArrayList.java:693)
at com.gaurav.ExProject.ArrayList.ArrayListRemoveAllNullPointerException.main(ArrayListRemoveAllNullPointerException.java:43)
Conclusion
The removeAll(Collection c) method removes from this list all of its elements that are contained in the specified collection.
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public boolean removeAll(Collection<?> c)
The example Java program used in the above article can be found at this GitHub repository.
Please write your thoughts in the comment section below.
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