hello,
Singleton is a concept in which you can create only object of a class.
You can achive this features by making class constructor private, and write a single static method (single entry) for object creation.
ex.
public class SingletonExample{
public static SingletonExample obj= null;
private SingletonExample(){
}
public static SingletonExample getClassObj(){
if(obj == null){
obj = new SingletonExample();
}
return obj;
}

}
Test class
public class test{
public static void main(String arg[]){
System.out.println(SingletonExample.getClassObj().toString);
System.out.println(SingletonExample.getClassObj().toString);
}
}

o/p both print same string representation of obj

Let me know if u have any doubt on this.
Thanks