JAVA : Accessing static method properly

Question

I am new to JAVA, and I like to try and understand everything.

When accessing a static method "hero.returnHp()" in JAVA, I have the following:

 hero Mike = new hero();

 Mike.returnHp();

The program runs fine, but I notice that Eclipse has a warning stating, "The static method from the type hero should be accessed in a static way." When I accept the auto-fix, it changes "Mike.returnHp();" to "hero.returnHp();".

So I have two questions:

1) What is the advantage of this?

2) If I created two objects of the same type, how would I specify which one to return when accessing in a static way?

Thanks!

Answer 1

I would first like to point out what the keyword static means.

Static variables only exist once per class – that is, if you create a class with a static variable then all instances of that class will share that one variable. Furthermore, if it’s a public static variable, then anyone can access the variable without having to first create an instance of that class – they just call Hero.staticVariableName;

Static method/functions are stateless. That is, they act only on information (1) provided by arguments passed to the method/function, or (2) in static variables (named above), or (3) that is hard-coded into the method/function (e.g. you create a static function to return “hello” – then “hello” is hard-coded into the function).

The reason why Eclipse wants you to access static methods in a static way is because it lets you and subsequent programmers see that the method you’re accessing is static (this helps to prevent mistakes). The function will run either way you do it, but the correct way to do it is to access static functions in a static way. Remember that if you call a static method, no matter what instance variable you call it from (Tim.returnHp, Jim.returnHp, Mike.returnHp, whatever) you will call the same function from the hero class and you will see the exact same behavior no matter who you call it from.

If you created two objects of the same type then you COULD NOT specify which one to return when accessing in a static way; static functions/methods will refer to the entire Hero class.

Can you explain what you’re trying to do so that we can offer more specific feedback? It’s quite possible that returnHp() shouldn’t be static.

Is that “return hit points”? If it is, then you do NOT want it static because the number of hit points that a hero has is part of the hero’s state, and static methods are stateless. (Think of state like the current condition – alive, dead, wounded, attacking, defending, some combination of the aforementioned, etc.) I would recommend going into the Hero class and changing returnHp to a non-static method.

Now… I know you didn’t ask, but I would like to advise you of something:

Class names (such as Hero) should be capitalized. Instance variable names (such as mike) should be lowercase. This is a widely accepted naming convention and it will increase the readability of your code.

Jeff