Internal Working of Hashset

Hashset internally use HashMap.

Key -> Input Value

Value -> Default PRESENT object

public class HashSet<E>
    extends AbstractSet<E>
    implements Set<E>, Cloneable, java.io.Serializable
{
private transient HashMap<E,Object> map;

// Dummy value to associate with an Object in the backing Map
private static final Object PRESENT = new Object();

/**
 * Constructs a new, empty set; the backing {@code HashMap} instance has
 * default initial capacity (16) and load factor (0.75).
 */
public HashSet() {
    map = new HashMap<>();
}
public boolean add(E e) {
    return map.put(e, PRESENT)==null;
}
public boolean remove(Object o) {
    return map.remove(o)==PRESENT;
}




import java.util.HashSet;
  
class Test
{    
    public static void main(String args[]) 
    {
        // creating a HashSet
        HashSet hs = new HashSet();
          
        // adding elements to hashset
        // using add() method
        boolean b1 = hs.add("Test");
        boolean b2 = hs.add("Test1");
          
        // adding duplicate element
        boolean b3 = hs.add("Test");
          
        // printing b1, b2, b3
        System.out.println("b1 = "+b1);
        System.out.println("b2 = "+b2);
        System.out.println("b3 = "+b3);
          
        // printing all elements of hashset
        System.out.println(hs);
              
    }
}
Output:

b1 = true
b2 = true
b3 = false
[Test, Test1]

Comments

Post a Comment

Popular posts from this blog

Java 8 : Find the number starts with 1 from a list of integers

  List<Integer> list = List. of ( 12 , 32 , 14 , 15 , 56 ); //Result->12,14,15 List<String> listString = list.stream().map(String::valueOf).collect(Collectors.toList()); List<String> result1 = listString.stream().filter(x->x.startsWith( "1" )) .collect(Collectors.toList()); System. out .println( "result1-->" +result1); List<String> result2 = list.stream().map(x->x+ "" ).filter(x->x.startsWith( "1" )) .collect(Collectors.toList()); System. out .println( "result2-->" +result2);
Read more

RDS vs Aurora DB

 1) Backtrack/Point in Time Restore (PITR) RDS Point in time restore is restore is supported, but it requires another RDS instance to be launched. Aurora Backtracks lets you quickly rewind the DB cluster to a specific point in time, without having to create another DB cluster. 2) Engine Options - Differences RDS - No concept of Global DB. Aurora - Global DB, Primary DB in one region and secondary DB in another region. 3) Compatibility with DB engines Aurora is compatible with two DBMSs namely PostgreSQL and MySQL. It is compatible with PostgreSQL 9.6.1 and MySQL 5.6. This means that you can run your existing database tools and applications on Aurora without any modifications.  On the other hand, Amazon RDS requires you to use AWS Database Migration Service to migrate from EC2-hosted or on-premises databases such as MySQL, PostgreSQL, MariaDB, Microsoft SQL Server, and Oracle. 4) Failover In RDS, Failover to read replica is done manually, which could lead to data loss. You can ...
Read more

Junit Mockito and Power Mockito

Mock vs Spy Both can be used to mock methods or fields. The difference is that  in mock, you are creating a complete mock or fake object while in spy, there is the real object and you just spying or stubbing specific methods of it . Mock vs InjectMock @Mock  creates a mock.  @InjectMocks  creates an instance of the class and injects the mocks that are created with the  @Mock  (or  @Spy ) annotations into this instance. Unit Testing Void Methods with Mockito and JUnit How to Test Void Methods  As we already know that our aim is to test void methods in a class. But it is also really important to understand why we test void methods.  Whenever we write unit test cases for any method, we expect a return value from the method. Generally, we use assert for checking if the method returns the value that we expect it to return, but in the case of void methods, they do not return any value. So how do we check if our method is functioning properly? Let’s...
Read more