Remove collection from a Set

boolean removeAll(Collection<?> c)

    Removes from this set all of its elements that are contained in the specified collection. return true if this set changed as a result of the call.

import java.util.*;
class SetRemoveAll{
 public static void main(String args[]){
  Set<Integer> mySet = new HashSet<> ();
  List<Integer> myList = new ArrayList<> ();
  
  /* Add Elements to mySet */
  mySet.add(10);
  mySet.add(20);
  mySet.add(30);
  
  /* Add Elements to myList */
  myList.add(20);
  myList.add(30);
  myList.add(40);
  
  System.out.println("\nElements in mySet are ");
  System.out.println(mySet);
  
  System.out.println("\nElements in myList are ");
  System.out.println(myList);
  
  mySet.removeAll(myList);
  
  System.out.println("\nElements after calling removeAll is ");
  System.out.println(mySet);
 }
}

Output

Elements in mySet are
[20, 10, 30]

Elements in myList are
[20, 30, 40]

Elements after calling removeAll is
[10]

1. throws ClassCastException if the class of an element of this set is incompatible with the specified collection 

2. throws UnsupportedOperationException if the removeAll operation is not supported by this set.

import java.util.*;
class SetRemoveAllUnsupported{
 public static void main(String args[]){
  Set<Integer> mySet = new HashSet<> ();
  Set<Integer> unmodifiable;
  List<Integer> myList = new ArrayList<> ();
  
  /* Add Elements to mySet */
  mySet.add(10);
  mySet.add(20);
  mySet.add(30);
  
  /* Create a unmodifiable Set*/
  unmodifiable = Collections.unmodifiableSet(mySet);
  
  /* Add Elements to myList */
  myList.add(20);
  myList.add(30);
  myList.add(40);
  
  System.out.println("\nElements in mySet are ");
  System.out.println(mySet);
  
  System.out.println("\nElements in myList are ");
  System.out.println(myList);
  
  /*Trying to perform removeAll on unmodifiable Set */
  unmodifiable.removeAll(myList);
  
  System.out.println("\nElements after calling removeAll is ");
  System.out.println(unmodifiable);
 }
}

Output

Elements in mySet are
[20, 10, 30]

Elements in myList are
[20, 30, 40]
Exception in thread "main" java.lang.UnsupportedOperationException
        at java.util.Collections$UnmodifiableCollection.removeAll(Unknown Source)
        at SetRemoveAllUnsupported.main(SetRemoveAllUnsupported.java:28)

3. throws NullPointerException if this set contains a null element and the specified collection does not permit null elements or if the specified collection is null.

import java.util.*;
class SetRemoveAllNullPointer{
 public static void main(String args[]){
  Set<Integer> mySet = new TreeSet<> ();
  List<Integer> myList = null;
  
  /* Add Elements to mySet */
  mySet.add(10);
  mySet.add(20);
  mySet.add(30);
  
  
  System.out.println("\nElements in mySet are ");
  System.out.println(mySet);
  
  System.out.println("\nElements in myList are ");
  System.out.println(myList+"\n");
  
  mySet.removeAll(myList);
  
  System.out.println("\nElements after calling removeAll is ");
  System.out.println(mySet);
 }
}

Output

Elements in mySet are
[10, 20, 30]

Elements in myList are
null

Exception in thread "main" java.lang.NullPointerException
        at java.util.AbstractSet.removeAll(Unknown Source)
        at SetRemoveAllNullPointer.main(SetRemoveAllNullPointer.java:19)

As you observe the program, myList is null, trying to remove myList from mySet causes the NullPointerException.

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