Singleton Class Using Private Constructor Java Example Program

Syntax

class ClassName
{
    static ClassName instance = null;
   
    private ClassName() {  }
  
    static public ClassName getInstance()
    {
        if (instance == null)        
             instance = new Singleton();
  
        return instance;
    } 
}

//Usage
ClassName instance = ClassName.getInstance();

Singleton Class Example Program

class Singleton
{
    static Singleton instance = null;
    public int instanceValue = 10;
   
    private Singleton() {  }
  
    static public Singleton getInstance()
    {
        if (instance == null)        
             instance = new Singleton();
  
        return instance;
    } 
}

public class SingletonClass {
    public static void main(String args[])    
   {
       Singleton instance1 = Singleton.getInstance();
       Singleton instance2 = Singleton.getInstance();
       
       //Objects are different
       //But same instance will be used
       instance1.instanceValue = instance1.instanceValue + 10;
       System.out.println("Value of instance1.instanceValue = " + instance1.instanceValue);
       System.out.println("Value of instance2.instanceValue = " + instance2.instanceValue);
   }    
}

Sample Output

Value of instance1.instanceValue = 20
Value of instance2.instanceValue = 20

Basic Programs

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2. Constructor Example Java Program
3. Parametrized Method Example Java Program
4. Static Class and Its Usage in Java Example Program
5. Static Function or Method and Its Usage in Java Example Program
6. Default and Parameterized Constructor Java Example Program
7. Constructor Chaining Java Example Program
8. Singleton Class Using Private Constructor Java Example Program
9. Constructor Overloading Example Java Program
10. Simple Class and Array of Object Java Example Program

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