Java ArrayList removeAll() Method

The removeAll() method of Java ArrayList class removes all the elements from a list that are contained in the specified collection.

Syntax:

Parameter:

"c": collection that contained elements to be removed from this list.

Return:

True if the original list changed as a result of this call.

Exception:

java.lang.NullPointerException: If the specified collection is null, or if the original list contains null elements and the specified collection does not permit null elements.

ClassCastException: if the class of an element of the original list is incompatible with the specified collection.

Example 1

import java.util.ArrayList;
public class ArrayListRemoveAllExample1
{
ArrayList<String> letters = new ArrayList<>();
letters.add("A");
letters.add("B");
letters.add("C");
letters.add("D");	
letters.add("E");
System.out.println(letters);	// [A, B, C, D, E]
ArrayList<String>removedLetters = new ArrayList<>();
removedLetters.add("C");
removedLetters.add("D");
removedLetters.add("E");
System.out.println(removedLetters);	// [C, D, E]
System.out.println(letters.removeAll(removedLetters)); //true
System.out.println(letters);		// [A, B]
}

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Output:

[A, B, C, D, E]
[C, D, E]
true
[A, B]

Example 2

import java.util.ArrayList;
public class ArrayListRemoveAllExample2
{
ArrayList<String> letters = new ArrayList<>();
letters.add("A");
letters.add("B");
letters.add("C");
letters.add("D");	
System.out.println(letters);	// [A, B, C, D]
ArrayList<Integer> numbers = new ArrayList<>();
numbers.add(1);
numbers.add(2);
letters.removeAll(numbers);	// throw  ClassCastException
}

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Output:

[A, B, C, D]

Example 3

import java.util.ArrayList;
public class ArrayListRemoveAllExample3
{
ArrayList<String> letters = null;    
System.out.println(letters);	// null
ArrayList<String>removedLetters = new ArrayList<>();
removedLetters.add("a");
removedLetters.add("b");
System.out.println(removedLetters);	// [a, b]
letters.removeAll(removedLetters);	// throw NullPointerException
}

Test it Now

Output: