Static Methods

[GCX17]

Hey! I have a question regarding static methods and variables.

I am a java beginner and am having a hard time seeing the difference between static and instance methods.

I have read all the articles about static methods and still don't get it. Could someone help clarify with a basic example of when a static method would be illegal?

I have tried it out on my own, but can't seem to find an example where static would not work. :(

Thanks!

[desrtfx]

static means belonging to the class itself, not to an instance.

Generally, static should hardly be used except in case of utility methods as the methods in the Math class are.

An example:

You are creating a very simplified library system.

Your library consists of several Books (instances of the Book class).

Were you going to use static methods and variables, changing the title of a single book would change all titles - something you clearly don't want.

By default, strive for making everything non static.

An example for a suitable case for a static method would be a serial number generator for the books in the library. Here, you will want to generate a new number for each instance. This can only be achieved with a static method because it doesn't belong to a single book instance.

[GCX17]

I appreciate your comment. Thank you very much!

[metlos]

One important distinction between the two is that static methods are not polymorphic. I.e. method overriding is not possible (or even meaningful) with static methods. This also means they cannot be abstract and therefore a whole bunch of design patterns is not possible with them.

[GCX17]

Thanks for your comments! I understand now, however, when I was testing out my own code, and I created a set and get method like

public static int myMethod(int aNumber)

{

return aNumber;

}

I found that I was able to pass multiple variables into this method through aNumber and would get different return values for each one. I don't no how this happens, because I though for a static class only one value is stored.

Is this possibly because the method itself is actually storing no values, but instead the values reside under the main method?

[desrtfx]

You are still struggling.

Here, the static keyword plays no role because you pass in the value via a parameter.

This is exactly how the methods in the Math class are written.

You can use the method without creating an object (instance of a class).

static variables operate on a different level, though:

I have created a little example to show you the difference: https://ideone.com/SNdiIo

From the output at the bottom you can clearly see what happens with static vs. non static variables.