1.Basic java example program to remove element hashset

• boolean remove(Object o) .   This method is used to remove element from hashset if it is present it returns true.

1. package com.getSizehashset;
2.  
3. import java.util.HashSet;
4. import java.util.Iterator;
5.  
6. public class HashsetExample{
7.  
8. public static void main(String[] args) {
9.   
10. //create object of HashSet
11.  HashSet<Integer> hashSet = new HashSet();
12.        
13.  //add elements to HashSet object
14.  hashSet.add(1);
15.  hashSet.add(2);
16.  hashSet.add(3);
17.  hashSet.add(4);
18.  hashSet.add(5);
19.  hashSet.add(6);
20.  hashSet.add(7);
21.  hashSet.add(8);
22.  
23. System.out.println("Size of HashSet after addition : " + hashSet.size());
24.  
25. System.out.println("Hashset contains");
26.  
27. Iterator it=hashSet.iterator();
28.              
29. while(it.hasNext()){
30. System.out.println(it.next());
31.                      
32. }   
33.  
34. boolean isRemoved = hashSet.remove(6);
35. System.out.println("Was 6 removed from HashSet ? " + isRemoved );
36.  
37. System.out.println("HashSet after removal : " + hashSet);
38. }
39.  
40. }
     

Output:

1. Size of HashSet after addition
2. 8
3. hashset contains
4. 1
5. 2
6. 3
7. 4
8. 5 
9. 6
10. 7
11. 8
12. Was 6 removed from HashSet ?true
13. HashSet after removal : [1, 2, 3, 4,5,7,8]

1.Basic java example program to get size of  hashset

• int size()   This method is used get get size of  hashset

1. package com.getSizehashset;
2.  
3. import java.util.HashSet;
4. import java.util.Iterator;
5.  
6. public class HashsetExample{
7.  
8. public static void main(String[] args) {
9.   
10. //create object of HashSet
11.  HashSet<Integer> hashSet = new HashSet();
12.        
13.  //add elements to HashSet object
14.  hashSet.add(1);
15.  hashSet.add(2);
16.  hashSet.add(3);
17.  hashSet.add(4);
18.  hashSet.add(5);
19.  hashSet.add(6);
20.  hashSet.add(7);
21.  hashSet.add(8);
22.  
23. System.out.println("Size of HashSet after addition : " + hashSet.size());
24.  
25. System.out.println("Hashset contains");
26.  
27. Iterator it=hashSet.iterator();
28.              
29. while(it.hasNext()){
30. System.out.println(it.next());
31.                      
32. }   
33.  
34. }
35.  
36. }
     

Output:

1. Size of HashSet after addition
2. 8
3. hashset contains
4. 1
5. 2
6. 3
7. 4
8. 5 
9. 6
10. 7
11. 8

1.Basic java example program to Copy all elements of Java HashSet to an Object Array

• Object[] toArray()   This method is used To copy all elements of java HashSet object into array use

1. package com.copyelementhashset;
2.  
3. import java.util.HashSet;
4. import java.util.Iterator;
5.  
6. public class HashsetExample{
7.  
8. public static void main(String[] args) {
9.   
10. //create object of HashSet
11.  HashSet<Integer> hashSet = new HashSet();
12.        
13.  //add elements to HashSet object
14.  hashSet.add(1);
15.  hashSet.add(2);
16.  hashSet.add(3);
17.  hashSet.add(4);
18.  hashSet.add(5);
19.      
20. Object[] objArray = hashSet.toArray();
21.  
22. //display contents of Object array
23. System.out.println("HashSet elements are copied into an Array. Now Array Contains..");
24.  
25.  for(int index=0; index < objArray.length ; index++)
26.   System.out.println(objArray[index]);
27. 
    
28.  
29. System.out.println("Hashset contains");
30.  
31. Iterator it=hashSet.iterator();
32.              
33. while(it.hasNext()){
34. System.out.println(it.next());
35.                      
36. }   
37.  
38. }
39.  
40. }
     

Output:

1. HashSet elements are copied into an Array. Now Array Contains..
2. 1
3. 2
4. 3
5. 4
6. 5
7. Hashset contains
8. 1
9. 2
10. 3
11. 4
12. 5

1.Basic java example program to check particular element is exists in hashset

• boolean contains(Object o)   This method Returns true if this set contains the specified element

1. package com.checkelementhashset;
2.  
3. import java.util.HashSet;
4. import java.util.Iterator;
5.  
6. public class HashsetExample{
7.  
8. public static void main(String[] args) {
9.   
10. //create object of HashSet
11.  HashSet<Integer> hashSet = new HashSet();
12.        
13.  //add elements to HashSet object
14.  hashSet.add(1);
15.  hashSet.add(2);
16.  hashSet.add(3);
17.  hashSet.add(4);
18.  hashSet.add(5);
19.      
20.  /*
21.  To check whether a particular value exists in HashSetwe need to use
22.   boolean contains(Object value) method of HashSet class.
23.  this method returns true if the HashSet contains the value, otherwise returns false.
24.  */
25.        
26.         boolean isExists = hashSet.contains(5);
27.         System.out.println("5 exists in HashSet ? : " + isExists);    
28.  
29. 
    
30.  
31. Iterator it=hashSet.iterator();
32.              
33. while(it.hasNext()){
34. System.out.println(it.next());
35.                      
36. }   
37.  
38. }
39.  
40. }
     

Output:

1. 3 exists in HashSet ? : true
2. 1
3. 2
4. 3
5. 4
6. 5

1.Basic Java example program to check particular key exists in hashmap

1. package com.javacheckkeyhashmap;
2.  
3. import java.util.Hashmap;
4. import java.util.Iterator;
5. import java.util.Map;
6. import java.util.Map.Entry;
7.  
8. public class HashmapExample{
9.  
10. public static void main(String[] args) {
11.   
12. //create an Hashmap object
13. HashMap<String, String> hashmap = new HashMap();
14.        
15. //Add key values pairs to hashmap
16.         
17. hashmap.put("1","One");
18. hashmap.put("2","Two");
19. hashmap.put("3","Three");
20. hashmap.put("4","Four");
21. hashmap.put("5","Five");
22. hashmap.put("6","Six");       
23.         
24.  
25.  /*
26.   To check whether a particular key exists in HashMap use
27.    boolean containsKey(Object key) method of HashMap class.
28.   containsKey(Object key) returns true if the HashMap contains mapping for specified key
29.   otherwise false.
30.  */
31.  
32. boolean isExists = hashmap.containsKey("4");
33. System.out.println("4 exists in HashMap ? : " + isExists);
34.     
35.  
36. if(!hashmap.isEmpty()){
37.  
38. Iterator it=hashmap.entrySet().iterator();
39.              
40. while(it.hasNext()){
41. 
    
42. Map.Entry obj=(Entry) it.next();
43. System.out.print(obj.getKey()+" ");
44. System.out.println(obj.getValue());
45.              
46. }           
47. }   
48.  
49. }
50.  
51. }
     

Output:

1. 4 exists in HashMap ? : true
2. 1 One
3. 2 Two
4. 3 Three
5. 4 Four
6. 5 Five
7. 6 Six