How do I compare 2 objects with 1 parameter?

Question

I made a java program that compares the distance between 2 objects

I managed to figure out how to solve it when I make a class with 2 parameters and compare these with the formula seen below;

public class RasterServices {

public static double distance (SimpleRasterElement a, SimpleRasterElement b) {
    
    double d;
    
    d = Math.sqrt(((b.x-a.x)*(b.x-a.x)) + ((b.y-a.y)*(b.y-a.y)));

    return d;
}

public class SimpleRasterElement {
      public int id;
      public double x;
      public double y;
      public double height;
}

public class SimpleRasterElementTest {

    public static void main (String[] args)
    {
        SimpleRasterElement a, b ;  // Deklarera variabeln
        
        a = new SimpleRasterElement (); // Skapa en instans (med ’new’),
        b = new SimpleRasterElement (); 
        
        // Tilldela variablerna i ’a’ värden:
        a.id = 1;
        a.x = 6.0;
        a.y = 8.0;
        a.height = 10.5;
        
        // Tilldela variablerna i ’b’ värden:
        b.id = 1;
        b.x = 9.0;
        b.y = 12.0;
        b.height = 15.5;

        System.out.println (RasterServices.distance(a,b));
        }
}

I can then test this via using my test program RasterServices.distance(a,b)

But now I want to make my variables private, use getters and create the distance() method within the RasterElement-class, and now I'm hardstuck.

public class RasterElementTest {

public static void main(String[] args) {
    
    RasterElement re_a = new RasterElement(1, 6.0, 8.0, 10.5);
    RasterElement re_b = new RasterElement(1, 9.0, 12.0, 15.5);
    
    double d = re_a.distance(re_b);

    System.out.println(d);

    }
}

asd

public class RasterElement {
private final int id;
private final double x;
private final double y;
private final double height;

public RasterElement (int id_nr, double x_val, double y_val, double height_val) {
    id = id_nr;
    x = x_val;
    y = y_val;
    height = height_val;
}

public int getId () {
    return id;
}

public double getX () { 
    return x;
}

public double getY () { 
    return y;
}

public double getHeight () { 
    return height;
}

public double distance (RasterElement a) {
    
    double d;
    
    d = Math.sqrt(((b.getX()-a.getX())*(b.getX()-a.getX())) + ((b.getY()-a.getY())*b.getY()-a.getY()));

    return d;
    }
}

But here in distance() i'm only allowed ONE parameter, can someone please explain to me how I can compare two elements/objects when I'm only allowed one parameter in the function?

(By using re_a.distance(re_b); in my test-code)

Thanks, sorry for the long post B-)

(how do I get the b-value into the equation in the method distance in the class RasterElement..?)

Answer 1

Change b to this . Also, you can eliminate d and return directly. Like,

public double distance (RasterElement a) {
    return Math.sqrt(((this.getX()-a.getX())*(this.getX()-a.getX()))
            + ((this.getY()-a.getY())*this.getY()-a.getY()));
}