What is a singleton class?

Solution:

Singleton class is the class which can not be instantiated more than once. To make a class singleton, we either make its constructor private or use the static getInstance method. Consider the following example.

class Singleton{  
    private static Singleton single_instance = null;  
    int i;  
     private Singleton ()  
     {  
         i=90;  
     }  
     public static Singleton getInstance()  
     {  
         if(single_instance == null)  
         {  
             single_instance = new Singleton();  
         }  
         return single_instance;  
     }  
}  
public class Main   
{  
    public static void main (String args[])  
    {  
        Singleton first = Singleton.getInstance();  
        System.out.println("First instance integer value:"+first.i);  
        first.i=first.i+90;  
        Singleton second = Singleton.getInstance();  
        System.out.println("Second instance integer value:"+second.i);  
    }  
}  
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