Java variable setting through method

Question

I have a method which takes in 4 floats and modifies the value. Now I would like to set the floats of the parent class to the value that the method took in. Some code:

public void influence(float x, float y, float w, float h){
x += 5; y += 5; w += 5; h += 5;
}

Now that would be called from the parent class like this:

float x = 5, y = 5, w = 5, h = 5;
influence(x, y, w, h);

I would like to set the floats in the parent to the modified method. I know I could return a float[] and then manually set the floats of the parent class to that array but is there a better way to do this? I could also use a class like Rect but that would be like an array.

You can't modify the callers values like that (and Java has no pointers). You could pass in an array of floats or you could return an array of floats (or a POJO) because that is passing the value of an Object reference. — Elliott Frisch, Aug 23 '14 at 00:55
You can't change parameters in Java, since all parameter forwarding in Java is by value. What you can do is either give POJO object to that method which will update it (do object.setX(object.getX()+5)), or I think better by design is that your object has method like object.influence(), which will change it's fields x, y, w, h... — Dejan Pekter, Aug 23 '14 at 01:01
I know but i was just wondering if there was ANY way to do it. Currently I am returning a float[]. — TameHog, Aug 23 '14 at 01:02
@TameHog No. You cannot change the value of primitives that are passed in. — markbernard, Aug 23 '14 at 01:20

score 2 · Accepted Answer · answered Aug 23 '14 at 01:11

Java does not have a way to pass a reference to a primitive. However, in your situation it would probably be better to avoid it anyway: it appears that the four variables are related to each other.

When several variables are related, they should be instance variables of a single object. Your object probably looks like a rectangular box that has the origin of (x, y), height h, and width w. Make a class for it, and let the method change that class, or return a new instance:

class Rect {
    private final float x, y, w, h;
    public float getX() { return x; }
    public float getY() { return y; }
    public float getW() { return w; }
    public float getH() { return h; }
    public Rect(float x, float y, float w, float h) {
        this.x = x;
        this.y = y;
        this.w = w;
        this.h = h;
    }
}

Then you can write a method returning a new Rect

public Rect influence(Rect inputRect) {
    ...
}

or make Rect mutable, and let influence modify its values.

score 1 · Answer 2 · edited May 23 '17 at 12:21

1

You can't change primitives in Java like that because everything in Jave is passed by value - but you can store the value in an array and pass it:

public void influence(float[] arr){
    for (int i=0; i<arr.length; i++){
        arr[i] += 5;
    }
}

edited May 23 '17 at 12:21

Community

1
1

answered Aug 23 '14 at 01:21

Nir Alfasi

53,191
11
86
129

Java variable setting through method

2 Answers2