Switch between class implementation

[Hamzah khammash]

Hi,
i create an interface and made 3 implementations for this interface and i also use singleton class to insure that only one object will created and this object will show the implementation of class depending on the number entered by the user for example if user enter 1 the implementation of class 1 will show to user and so on , i try to do something like this

 implementation for Singleton class
public class Singelton  implements Testable {
	 public static Singelton singelton=null;
	 
	 private Singelton() {
	}
    public static Testable getInstance(String str)
    {
    	int x=Integer.parseInt(str);
    	switch (x) {
		case 1:
			Test1 test=new Test1();
			break;
			

		default:
			break;
		}    	 
    	return singelton;
    	
    }
	@Override
	public void doSomething() {
		// TODO Auto-generated method stub
		
	}
	@Override
	public void doSomething(String str) {
		// TODO Auto-generated method stub
		
	}
	@Override
	public void doSomething(String str, int value) {
		// TODO Auto-generated method stub
		
	}
}

public class Main {
	Main() {
	}

	public static void main(String args[]) throws IOException {
		BufferedReader reader = new BufferedReader(new InputStreamReader(
				System.in));
		String input = reader.readLine();
		Testable singelton = Singelton.getInstance(input);
		
		

		
	}

}

package com.singelton;

import org.apache.log4j.Logger;
import org.apache.log4j.xml.DOMConfigurator;

public class Test1 implements Testable{
	Logger logger=Logger.getLogger(Singelton.class);

	public Test1() {
	 
		// TODO Auto-generated constructor stub
	doSomething();
	doSomething("Hello");
	doSomething("Hello ", 1);
	}
	public void doSomething() {
		DOMConfigurator.configure("log4j.xml");
		logger.info("Hello wold ");
		
	}

	@Override
	public void doSomething(String str) {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void doSomething(String str, int value) {
		// TODO Auto-generated method stub
		
	}
	

}

but i think i missed something and i dont know what is it .
so can anyone view my code and tell me if there anything wrong
Thanks

[John Jai]

in the Singleton:getInstance() method do you assign any object value to the returning reference singleton?

[Hamzah khammash]

In singleton.getInstance(String str) method i passed the value entered by the user to use it in the switch statement that create a object of another class and then return singleton of reference

[John Jai]

The reference you return is the one referred by the singleton variable... So the below line shouldn't be assigning the singleton reference?

Test1 test=new Test1();

[Hamzah khammash]

So how can i make a reference of class Test1 in this case ? Note that Test1 implements Testable interface and getInstance of type Testable also.

[John Jai]

singleton = new Test1();

Did you try above code?

Can you post the code for Testable interface?

[Hamzah khammash]

package com.singelton;

/**
 * @author h.khammash
 * Used by the Main class to test the Singleton .
 */
public interface Testable {

	public void doSomething();
	public void doSomething(String str);
	public void doSomething(String str,int value);
	
}

[John Jai]

Hamzah khammash wrote:Note that Test1 implements Testable interface and getInstance of type Testable also.

What does getInstance mean here... a method? if so I see only Singleton class has it... any ways did you figure out the mistake?

[Hamzah khammash]

getInstance() generate an instance if not exist and i think yes i figure my mistake using

singleton =new Test1

in switch statement and make singleton constructor protected

[John Jai]

So why are you making the Singleton class to implement Testable interface when you do nothing with the methods exposed by them?

[John Jai]

The Singleton implementation is bit flawed as it allows any number of instances to be created. I have modified it a to have one single instance.

public class Singleton {
	private static Testable singleton ;

	private Singleton(String str) {
		int x=Integer.parseInt(str);
		switch (x) {
		case 1:
			singleton = new Test1();
			break;
		default:
			break;
		}		
	}
	public static Testable getInstance(String str)
	{		    	 
		if (singleton == null){
			System.out.println("Creating new instance first time...");
			new Singleton(str);
		}
		return singleton;
	}
}

If you need to refer different implementations at different times in your logic, then you should probably use a factory method to create instances based on user input and not Singleton.