The Singleton pattern is a creational design pattern that ensures that only one instance of a class can be created and that the same instance is used every time the object is requested.
class Singleton {
// Static variable reference of single_instance
// of type Singleton
private static Singleton single_instance = null;
// Declaring a variable of type String
public String s;
// Constructor
// Here we will be creating private constructor
// restricted to this class itself
private Singleton()
{
s = "Hello I am a string part of Singleton class";
}
// Static method
// Static method to create instance of Singleton class
public static synchronized Singleton getInstance()
{
if (single_instance == null)
single_instance = new Singleton();
return single_instance;
}
}
// Class 2
// Main class
class TestingSinglTon {
// Main driver method
public static void main(String args[])
{
// Instantiating Singleton class with variable x
Singleton x = Singleton.getInstance();
// Instantiating Singleton class with variable y
Singleton y = Singleton.getInstance();
// Instantiating Singleton class with variable z
Singleton z = Singleton.getInstance();
// Printing the hash code for above variable as
// declared
System.out.println("Hashcode of x is " + x.hashCode());
System.out.println("Hashcode of y is "+ y.hashCode());
System.out.println("Hashcode of z is "+ z.hashCode());
// Condition check
if (x == y && y == z) {
// Print statement
System.out.println(
"Three objects point to the same memory location on the heap i.e, to the same object");
} else {
// Print statement
System.out.println(
"Three objects DO NOT point to the same memory location on the heap");
}
}
}
Output:
====================================
Hashcode of x is 558638686
Hashcode of y is 558638686
Hashcode of z is 558638686
Three objects point to the same memory location on the heap i.e, to the same object
