Instantiating a class with private constructor

[ragi singh]

Hello all,

I am preparing for SCJP and was reading rules for constructors however , there is an extract in the book about classes with private constructors which is as follows:-

Constructors can use any access modifier, including private. (A private constructor means only code within the class itself can instantiate an object of that type, so if the private constructor class wants to allow an instance of the class to be used, the class must provide a static method or variable that allows access to an instance created from within the class.)


Can anyone explain with a relevant example how are we going to instantiate this class with private constructor ?

[Ernest Friedman-Hill]

You can use the one Example object in the public static variable INSTANCE, but you can't create any more:

public class Example {
    public static final INSTANCE = new Example();
    private Example() {}
}

[ragi singh]

ok thank you i got the point .

[Hunter McMillen]

look up the singleton pattern for a real world use of what you're talking about.
Singleton Pattern

Ex:

    
public class Singleton {
   private static final Singleton INSTANCE = new Singleton();
 
   // Private constructor prevents instantiation from other classes
   private Singleton() {}
 
   public static Singleton getInstance() {
      return INSTANCE;
   }
 }