Imp. Points to Remember :
- We can make constructor as private. So that We can not create an object outside of the class.
- This property is useful to create singleton class in java.
- Singleton pattern helps us to keep only one instance of a class at any time.
- The purpose of singleton is to control object creation by keeping private constructor.
The easiest implementation consists of a private constructor and a field to hold its result, and a static accessor method with a name like getInstance().
The private field can be assigned from within a static initializer block or, more simply, using an initializer. The getInstance( ) method (which must be public) then simply returns this instance:
//File Name: Singleton.java
public class Singleton
{
private static singleton ;
//A private constructor
private Singleton(){ }
public class Singleton
{
private static singleton ;
//A private constructor
private Singleton(){ }
//Static Instance Method
public static Singleton getInstance()
{
singleton=new Singleton();
return singleton;
}
//Other method
protected static void demoMethod()
{
system.out.println("demomethod for singleton");
}
}
public static Singleton getInstance()
{
singleton=new Singleton();
return singleton;
}
//Other method
protected static void demoMethod()
{
system.out.println("demomethod for singleton");
}
}
Here is the main program file where we will create singleton object:
//FileName :SingletonDemo.java
public class SingletonDemo
{
public static void main(String args[])
{
Singleton tmp=Singleton.getInstance();
tmp.demoMethod();
}
}
public class SingletonDemo
{
public static void main(String args[])
{
Singleton tmp=Singleton.getInstance();
tmp.demoMethod();
}
}
This would produce the following result:
demomethod for singleton
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