Abstract Class with Static Methods

[bugger]

I am in need of an advice. I am designing my application and want to know when to use abstract class with static methods?

Abstract calls cannot be instantiated. If I don't declare the methods in Abstract class static, how can I call them?

Thanks.
--------

[CaptainMorgan]

Quote:

Originally Posted by bugger

I am in need of an advice. I am designing my application and want to know when to use abstract class with static methods?

Abstract calls cannot be instantiated. If I don't declare the methods in Abstract class static, how can I call them?

Thanks.
--------

If I understand your question correctly, you simply need to extend the abstract class.

Code:

public abstract class AbstractExample {
  public static void foo() {
    System.out.println("Static foo called.");
  }
  
  public void bar() {
    System.out.println("Non-static bar called.");
  }  
}

Code:

public class AbstractCaller extends AbstractExample {
  public static void main(String[] args) {
    AbstractCaller ac = new AbstractCaller();
    ac.foo();
    ac.bar();
  }      
}

Output:
Static foo called.
Non-static bar called.

Hope this helps, see this Sun topic for more info.

[bugger]

Thanks.
But you are calling both methods (foo and bar) with the object (ac). What role the static method played here?

[tim]

Hello bugger

CaptainMorgan's example explains how to call the static and non-static methods and not why someone would like to do that. Static methods can only access static attributes of a instanced class. For example:

You have a class called Dog with a static field called numberOfDogs. In the constructor of Dog you can increment numberOfDogs and if you override the finalize method then you can decrement numberOfDogs. This way you can track how many Dog objects that you have created thanks to the static modifier. Now, you can add static methods to the Dog class to manipulate numberOfDogs without you having to create an instance of Dog

Hope this helped.

[bugger]

Thanks tim.
Got it.

[artem_korostelev]

I think that all of the above posts right.
But you guys are probably too experienced to answer the questions guys like me may ask (i am new to Java).

Two things here to understand : First of all, Abstract Class cannot be instantiated. And Second - you don't have to Instantiate class (including abstract by extending and etc) in order to call Static Method. SO STATIC METHOD IS OUR FRIEND HERE!!!!

Imagine this : You have Class Animal and you may want to have it Abstract. Then You have Static variable like Count of your Animals, and Static Method GetCount() to keep track of it. So you can call directly Animal.GetCount() without even extending our abstract class.


To CaptainMorgan : You sir right there, but the difference between static and non static is explicitely exposed below, I have changed your code slightly :

Code:
public abstract class AbstractExample {
public static void foo() {
System.out.println("Static foo called.");
}

public void bar() {
System.out.println("Non-static bar called.");
}
}Code:
public class AbstractCaller extends AbstractExample {
public static void main(String[] args) {
AbstractExample.foo(); \\ this is where we get our AnimalCount for exmple
AbstractCaller ac = new AbstractCaller();
\\ac.foo(); - NO NEED TO HAVE ac IF WE WANT TO CALL foo();
ac.bar();
}
}

[Supamagier]

True that, but:

1. Everything static just looks ugly. :P
2. Static methods/vars have limitations and disadvantanges you sometimes don't want.

Usually only the things that really need to be static are static, not the opposite.

I suggest: never make things static, unless you have no choice.

[artem_korostelev]

Quote:

Originally Posted by Supamagier

True that, but:

1. Everything static just looks ugly. :P
2. Static methods/vars have limitations and disadvantanges you sometimes don't want.

Usually only the things that really need to be static are static, not the opposite.

I suggest: never make things static, unless you have no choice.

What's Static is Static sir. What is not Static is not Static, you can't replace one thing with another.

In simple words, for instance
Total Count of Items is Static, you cant make it any other type.
Color of the item can not be static, since it is different from instance to instance.

I am sorry but its not something redundant. Static type there for a reason.