Calling a method from main method

Question

When I am calling a method directly from main method, it is not allowed. However, when I am calling the same method from the constructor of a class, it is allowed.

The allowed version;

public class App {

Integer firstVariable;
Integer secondVariable;

public static void main(String[] args) {
    App obj = new App(3, 2);
}

public App(Integer firstVariable, Integer secondVariable) {
    this.firstVariable = firstVariable;
    this.secondVariable = secondVariable;

    this.calculate(firstVariable, secondVariable);
}

public int calculate(int a, int b) {
    int result = a + b;

    return result;
}
}

The disallowed version;

public class App {

Integer firstVariable;
Integer secondVariable;

public static void main(String[] args) {
    App obj = new App(3, 2);

    obj.calculate(firstVariable, secondVariable);
}

public App(Integer firstVariable, Integer secondVariable) {
    this.firstVariable = firstVariable;
    this.secondVariable = secondVariable;

}

public int calculate(int a, int b) {
    int result = a + b;
    return result;
}
}

I know it is "Cannot make a static reference to the non-static field firstVariable" error. My question is; In both code blocks, the same thing is done but what is the difference between them?

@Jan I know. It does not belong to any class. How can I call a method, which belongs to an object from the main method. — Bernhard Colby, Dec 25 '15 at 18:59
@BernhardColby Just as you use `obj.calculate`, use `obj.firstVariable` — Thiyagu, Dec 25 '15 at 19:00
have you tried `obj.calculate(obj.firstVariable, obj.secondVariable);`? those two aren't static. — WalterM, Dec 25 '15 at 19:00

yngwietiger · Accepted Answer · 2015-12-25T19:05:03.943

1

The issue isn't your method. The issue is that your variables (the arguments that you're trying to pass) are being referenced from a static context.

edited Dec 25 '15 at 19:05

answered Dec 25 '15 at 19:01

yngwietiger

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Why the downvote? What I say is true. It's not the method, it's the arguments he's trying to pass that are the problem. I even pulled the code up in IntelliJ, and that's what it's complaining about. – yngwietiger Dec 25 '15 at 19:03
I didn't downvote, but the problem is actually that the variables _are not_ static, which is why you can't use them in `main`. – Mick Mnemonic Dec 25 '15 at 19:04
Right. I fixed my comment. What I meant is that he's trying to reference them from a static context. – yngwietiger Dec 25 '15 at 19:05

Calling a method from main method

1 Answers1