How to assign class variable value via calling a method?

Question

I am trying to assign value to a class variable via a method. However, after the execution comes out of the scope of the method, the variable is still initialized to the default value. How do we accomplish this in Java?

I want to initialize x to 5 by calling the method hello(). I don't want to initialize by using a constructor, or using this. Is it possible?

public class Test {
    int x;
    public void hello(){
        hello(5,x);
    }
    private void hello(int i, int x2) {
        x2 = i;
    }
    public static void main(String args[]){
        Test test = new Test();
        test.hello();
        System.out.println(test.x);
    }
}

You should read this: Is Java "pass-by-reference" or "pass-by-value"? — Tom
– Tom, Commented Jun 5, 2015 at 15:25

Community · Accepted Answer · 2017-05-23 11:51:08Z

9

When you do

hello(5,x);

and then

private void hello(int i, int x2) {
    x2 = i;
}

it seems like you might be trying to pass the field itself as parameter to the hello method, and when doing x2 = i you meant x2 to refer to the field. This is not possible, since Java only supports pass-by-value. I.e. whenever you give a variable as argument to a method, the value it contains will be passed, not the variable itself.

(Thanks @Tom for pointing out this interpretation of the question in the comments.)

edited May 23, 2017 at 11:51

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answered Jun 5, 2015 at 14:47

aioobe

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12 Comments

psychorama Over a year ago

I don't want to use 'this' either. Is there still a way?

Arnaud Denoyelle Over a year ago

@VisheshSrivastava Change the name of the variable instead. Your problem comes from the fact that your variable name shadows the attribute 's name. And btw, shadowing it is a bad practice.

JB Nizet Over a year ago

Yes: remove the useless arguments of the method hello, which are completely ignored. Or at least, don't name arguments the same way as instance fields.

NoseKnowsAll Over a year ago

@VisheshSrivastava Yes. Change the name of your input variable to something else, like int in_x or my favorite: int x_

JB Nizet Over a year ago

@VisheshSrivastava consider calling the method in your test. You're only calling the constructor.

|

Armand · Accepted Answer · 2015-06-05 14:50:18Z

1

The class property x is only visible by using this.x in hello() because you have declared another variable called x in the method's arguments.

Either remove that argument:

private void hello(int i) {
    x = 5;
}

Rename the argument:

private void hello(int i, int y) {
    x = 5;
}

Or use this.x to set the class property:

private void hello(int i, int x) {
    this.x = 5;
}

answered Jun 5, 2015 at 14:50

Armand

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Comments

aakansha · Accepted Answer · 2015-06-05 14:58:55Z

0

You can create two methods.

public void setX(int a)//sets the value of x
{
    x=a;
}
public int getX()//return the value of x
{
return x;
}

call setX to set the value of x and getx to return the value x.

Essentially these are called getter and setter and we use them to access private members from outside the class.

answered Jun 5, 2015 at 14:58

aakansha

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