Método HashSet removeAll() en Java con ejemplo

El método removeAll() de la clase java.util.HashSet se usa para eliminar de este conjunto todos sus elementos que están contenidos en la colección especificada.
Sintaxis: 

public boolean removeAll(Collection c)

Parámetros: este método toma la colección c como un parámetro que contiene elementos que se eliminarán de este conjunto.
Valor devuelto: este método devuelve verdadero si este conjunto cambió como resultado de la llamada.
Excepción: este método lanza NullPointerException si este conjunto contiene un elemento nulo y la colección especificada no permite elementos nulos (opcional), o si la colección especificada es nula.
A continuación se muestran los ejemplos para ilustrar el método removeAll() .
Ejemplo 1: 

// Java program to demonstrate
// removeAll() method for Integer value
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
 
        try {
 
            // Creating object of HashSet<Integer>
            HashSet<Integer>
                arrset1 = new HashSet<Integer>();
 
            // Populating arrset1
            arrset1.add(1);
            arrset1.add(2);
            arrset1.add(3);
            arrset1.add(4);
            arrset1.add(5);
 
            // print arrset1
            System.out.println("HashSet before "
                               + "removeAll() operation : "
                               + arrset1);
 
            // Creating another object of  HashSet<Integer>
            HashSet<Integer>
                arrset2 = new HashSet<Integer>();
            arrset2.add(1);
            arrset2.add(2);
            arrset2.add(3);
 
            // print arrset2
            System.out.println("Collection Elements"
                               + " to be removed : "
                               + arrset2);
 
            // Removing elements from arrset
            // specified in arrset2
            // using removeAll() method
            arrset1.removeAll(arrset2);
 
            // print arrset1
            System.out.println("HashSet after "
                               + "removeAll() operation : "
                               + arrset1);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

HashSet before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : [1, 2, 3]
HashSet after removeAll() operation : [4, 5]

Ejemplo 2: para NullPointerException 

// Java program to demonstrate
// removeAll() method for Integer value
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
 
        try {
 
            // Creating object of HashSet<Integer>
            HashSet<Integer>
                arrset1 = new HashSet<Integer>();
 
            // Populating arrset1
            arrset1.add(1);
            arrset1.add(2);
            arrset1.add(3);
            arrset1.add(4);
            arrset1.add(5);
 
            // print arrset1
            System.out.println("HashSet before "
                               + "removeAll() operation : "
                               + arrset1);
 
            // Creating another object of  HashSet<Integer>
            HashSet<Integer>
                arrset2 = null;
 
            // print arrset2
            System.out.println("Collection Elements"
                               + " to be removed : "
                               + arrset2);
 
            System.out.println("\nTrying to pass "
                               + "null as a specified element\n");
 
            // Removing elements from arrset
            // specified in arrset2
            // using removeAll() method
            arrset1.removeAll(arrset2);
 
            // print arrset1
            System.out.println("HashSet after "
                               + "removeAll() operation : "
                               + arrset1);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

HashSet before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : null

Trying to pass null as a specified element

Exception thrown : java.lang.NullPointerException