Can we create private constructor in java

1.Can a constructor in Java be private?

• Yes we can declare private constructor in java.
• If we declare constructor as private we can not able to create object of the class.
• In singleton design pattern we use this private constructor. 

 2.In what scenarios we will use private constructor in java.

•  Singleton Design pattern
• It wont allow class to be sub classed.
• It wont allow to create object outside the class.
• If All Constant methods is there in our class we can use private constructor.
• If all methods are static then we can use private constructor.

 3.What will happen if we extends a class which is having private constructor.

•  If we try to extend a class which is having private constructor compile time error will come.
• Implicit super constructor is not visible for default constructor. Must define an explicit constructor

Singleton Design pattern:

1. package com.privateConstructorSingleTon;
2.  
3. public class SingletonClass {
4. 
   
5. private static SingletonClass object;
6.  
7. private SingletonClass ()
8. {
9.         System.out.println("Singleton(): Private constructor invoked");
10. }
11.  
12. public static SingletonClass getInstance()
13. {
14.  
15. if (object == null)
16. {
17.  
18. System.out.println("getInstance(): First time getInstance was called and object created !");
19. object = new SingletonClass ();
20.  
21.  }
22.  
23. return object;
24.  
25. }
26.  
27. }
     

1. package instanceofjava;
2.  
3. public class SingletonObjectDemo {
4. 
   
5. public static void main(String args[]) {
6.  
7.      SingletonClass s1= SingletonClass .getInstance();
8.      SingletonClass s2= SingletonClass .getInstance();
9.      System.out.println(s1.hashCode());
10.      System.out.println(s2.hashCode());
11.  
12. }
13. }

Output:

1. getInstance(): First time getInstance was called and object created !
2. Singleton(): Private constructor invoked
3. 655022016
4. 655022016