Can not make static reference to non static method?

Question

So, in short. I have two classes.

package rpg;

public class Engine {
    public void main(String args[]) {
        Start.gameStart();
        System.out.println(menuResult);
    }
}

and

package rpg;
public class Start {
    int menuResult = 3;
    public int gameStart() 
    {
        return menuResult;
    }
    public int getMenuResult()
    {
        return Start.menuResult;
    }
}

It keeps throwing up the error 'Cannot make static reference to non-static method gameStart()'. I'm sure I'm missing something simple, but can't find it. Thanks!

score 8 · Accepted Answer · answered Oct 11 '12 at 14:15

8

You need to create instance of Start class and call gameStart() method on that instance because gameStart() is instance method not static method.

 public void main(String args[]) {
       new Start().gameStart();
       ..................
  }

Only static methods can be accessed by using class name as perfix.

answered Oct 11 '12 at 14:15

kosa

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So... what exactly is `new Start().gameStart();` doing? It seems like it's creating an object, but how would I call it? – Cowthulhu Oct 11 '12 at 14:44
2

You are creating an instance (object) for Start() class and calling gameStart() method of that instance (remember gameStart() is instance method). – kosa Oct 11 '12 at 14:47
It creates a new object and then it calls method gameStart() on this object. – Jiri Kremser Oct 11 '12 at 14:48

Amit Deshpande · Answer 2 · 2012-10-11T14:30:34.187

3

public int gameStart() <--- Instance method not static method

call it on instance

 Start start = new Start();
 start.gameStart();

So finally your classes should look like below

public static void main(String args[]) {
    Start start = new Start();
    start.gameStart();
    System.out.println(start.getMenuResult());
}

public class Start {
   private int menuResult = 3;
    public int gameStart() {
        return this.menuResult;//Don't know why there are two methods
    }
    public int getMenuResult() {
        return this.menuResult;
    }
}

edited Oct 11 '12 at 14:30

answered Oct 11 '12 at 14:15

Amit Deshpande

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Notice that, if `gameStart()` were made static, that would just the first domino stone to fall down, followed by the rest of the whole `Start` class. Clearly not OP's intention. – Marko Topolnik Oct 11 '12 at 14:28
Clearly forgot to add make `menuResult` also static. Thanks. – Amit Deshpande Oct 11 '12 at 14:31
... then followed by making `getMenuResult` static as well :) – Marko Topolnik Oct 11 '12 at 14:32

score 2 · Answer 3 · answered Oct 11 '12 at 14:18

first of all the main method should be

public static void main(String args[]) {

}

I assume you can have multiple games, and hence you should be able to start multiple instances so you should create a non static class that can be created and then actions performed against.

to answer your original question, you need to have a static variable that have static getters and setters..

public class Start {
    private static int menuResult = 3;
    public static int gameStart() 
    {
        return menuResult;
    }
    public static int getMenuResult()
    {
        return Start.menuResult;
    }

score 0 · Answer 4 · answered Oct 11 '12 at 14:17

If you need the method to be static, just add the keyword static in the function definition. That would get rid of the error. But if you want to keep the class Start the way it is, then you should create an instance of Start in the main function and then call the method. Hope that helps!

score 0 · Answer 5 · answered Oct 11 '12 at 14:23

0

you are trying to invoke a method on its class name. you should be creating a new object and invoke its method

public void main(String args[]) {
        new Start().gameStart();
        System.out.println(menuResult);
    }

answered Oct 11 '12 at 14:23

PermGenError

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score 0 · Answer 6 · answered Oct 11 '12 at 14:25

Start.gameStart() refers to a method which would be public static int gameStart() because Start is the class and not an instance of the object.

If you declare a method on an object, you need to apply it to instance of the object and not its class.

When to use static or instanciated methods ?

instanciated : whenever you need to apply the method to the object you're in. example : mycake.cook();
static : when the actions you do inside your method have nothing to do with an object in particular. example : Cake.throwThemAll();

mycake is an instance of a Cake, declared this way : Cake mycake = new Cake();

Cake is the class representing the object.

You should, i guess, have a read at some object oriented programmation course if you still have a doubt about objects, classes and instances.

score 0 · Answer 7 · answered Oct 11 '12 at 14:33

While Other answers are Correct , that remains the Question that Why you Can't access Instance method Directly from Class name , In Java all static (methods , fields) bind with Class Name and when Class Is Loading to the Memory (Stack) all static members are Loading to the Stack , and this time Instance Method is not visible to Class. instance Method will Load into Heap portion in the memory and can only be access by Object references .

Can not make static reference to non static method?

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