HashSet removeAll() method in java

public boolean removeAll(Collection<?> c){

   }

• Parameters – c collection containing elements to be removed from this Set.
• Returns Value-  It return true if this set changed as a result of the call.
• Exception –  It throws following exceptions :
  UnsupportedOperationException – if the removeAll operation is not supported by this set
  ClassCastException – if the class of an element of this set is incompatible with the specified collection.
  NullPointerException – if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null.

Example 1 : Java HashSet removeAll() method – Elements Present

In this example , We will create HashSet of String and add elements into HashSet using add() method. We shall then use removeAll() method to remove elements from HashSet .

import java.util.HashSet;

public class HashSeteemoveAll {

	public static void main(String[] args) {

		// Constructs a new, empty set
		HashSet<String> hashSet = new HashSet<String>();

		// add element in it
		hashSet.add("java");
		hashSet.add("welcomes");
		hashSet.add("you");
		hashSet.add("to");
		hashSet.add("learn");

		// display the element
		System.out.println("element in hashset =" + hashSet);

		HashSet<String> hashSet2 = new HashSet<String>();
		hashSet2.add("you");
		hashSet2.add("learn");

		System.out.println("Collection Elements to be removed : " + hashSet2);

		// removing element using removeAll() method
		boolean isElementsRemoved = hashSet.removeAll(hashSet2);

		System.out.println("is Elements removed From HashSet ? "
				+ isElementsRemoved);

		System.out.println("After Remove elements hashset is =" + hashSet);

	}

}

Output:

element in hashset =[welcomes, java, learn, to, you]
Collection Elements to be removed : [learn, you]
is Elements removed From HashSet ? true
After Remove elements hashset is =[welcomes, java, to]

Example 2 : Java HashSet removeAll() method – Elements not Present

We will initialize HashSet with String elements. Then we shalll use removeAll() method but elements of provide collection is not present in HashSet.

import java.util.HashSet;

public class HashSeteemoveAll1 {
	
	public static void main(String[] args) {
		
		// Constructs a new, empty set
		HashSet<String> hashSet = new HashSet<String>();

		// add element in it
		hashSet.add("java");
		hashSet.add("welcomes");
		hashSet.add("you");
		hashSet.add("to");
		hashSet.add("learn");

		// display the element
		System.out.println("element in hashset =" + hashSet);

		HashSet<String> hashSet2 = new HashSet<String>();
		hashSet2.add("android");
		hashSet2.add("php");
		
		System.out.println("Collection Elements to be removed : "+ hashSet2 );
	
		//removing element using removeAll() method
		boolean isElementsRemoved =  hashSet.removeAll(hashSet2);
		
	System.out.println("is Elements removed From HashSet ? "+ isElementsRemoved );

	System.out.println("After Remove elements hashset is =" + hashSet);

	}

}

Output:

element in hashset =[welcomes, java, learn, to, you]
Collection Elements to be removed : [android, php]
is Elements removed From HashSet ? false
After Remove elements hashset is =[welcomes, java, learn, to, you]

Example 3 : Java HashSet removeAll() method – NullPointerException

Let’s see example of HashSet removeAll() method for NullPointerException. We will provides null collection to removeAll() method , then it will throw null pointer exception .

import java.util.HashSet;

public class HashSeteemoveAll2 {

	public static void main(String[] args) {

		// Constructs a new, empty set
		HashSet<String> hashSet = new HashSet<String>();

		// add element in it
		hashSet.add("java");
		hashSet.add("welcomes");
		hashSet.add("you");
		hashSet.add("to");
		hashSet.add("learn");

		// display the element
		System.out.println("element in hashset =" + hashSet);

		HashSet<String> hashSet2 = null;

		System.out.println("Collection Elements to be removed : " + hashSet2);
		try {
			// removing element using removeAll() method
			boolean isElementsRemoved = hashSet.removeAll(hashSet2);

			System.out.println("is Elements removed From HashSet ? "
					+ isElementsRemoved);

			System.out.println("After Remove elements hashset is =" + hashSet);
		} catch (NullPointerException e) {
			System.out.println("Exception : " + e);
		}

	}

}

Output:

element in hashset =[welcomes, java, learn, to, you]
Collection Elements to be removed : null
Exception : java.lang.NullPointerException

In this tutorial we learned hashset removeall() method in java . You can learn more java HashSet example for practice .

A Guide to HashSet