hashset remove 28object o 29 method in java

1import java.util.HashSet;
2public class HashSetRemoveObjectMethodExample
3{
4   public static void main(String[] args)
5   {
6      HashSet<String> hs = new HashSet<String>();
7      hs.add("hello");
8      hs.add("world");
9      hs.add("java");
10      System.out.println("HashSet before using remove(Object o) method: " + hs);
11      // remove string "world" from HashSet
12      boolean bool = hs.remove("world");
13      System.out.println("Has string removed? " + bool);
14      System.out.println("HashSet after using remove(Object o) method: " + hs);
15   }
16}

1example on removeAll() method for NullPointerException
2import java.util.HashSet;
3public class HashSetRemoveAllMethodExample
4{
5   public static void main(String[] args)
6   {
7      try
8      {
9         HashSet<Integer> hs1 = new HashSet<Integer>();
10         hs1.add(2);
11         hs1.add(4);
12         hs1.add(6);
13         hs1.add(8);
14         hs1.add(10);
15         // printing hs1
16         System.out.println("HashSet before using removeAll() method: " + hs1);
17         // create another object of HashSet
18         HashSet<Integer> hs2 = null;
19         // printing hs2
20         System.out.println("Elements to be removed: " + hs2);
21         System.out.println("Trying to pass null: ");
22         // removing elements from HashSet
23         // specified in hs2 using removeAll() method
24         hs1.removeAll(hs2);
25         System.out.println("HashSet after using removeAll() method: " + hs1);
26      }
27      catch(NullPointerException ex)
28      {
29         System.out.println("Exception: " + ex);
30      }
31   }
32}

1import java.util.HashSet;
2public class HashSetRemoveAllMethodExample
3{
4   public static void main(String[] args)
5   {
6      try
7      {
8         HashSet<Integer> hs1 = new HashSet<Integer>();
9         hs1.add(2);
10         hs1.add(4);
11         hs1.add(6);
12         hs1.add(8);
13         hs1.add(10);
14         System.out.println("HashSet before using removeAll() method: " + hs1);
15         // create another HashSet
16         HashSet<Integer> hs2 = new HashSet<Integer>();
17         hs2.add(2);
18         hs2.add(4);
19         hs2.add(6);
20         System.out.println("Elements to be removed: " + hs2);
21         // remove elements from hs1 described in hs2 using removeAll() method
22         hs1.removeAll(hs2);
23         System.out.println("HashSet after using removeAll() method: " + hs1);
24      }
25      catch(NullPointerException ex)
26      {
27         System.out.println("Exception: " + ex);
28      }
29   }
30}