method call problem

Hello, I have been learning Java just for a few days and right in my first little assignment I got stuck.
Here is the code:

Code:

---

public class Vertex
{
  private double x;
  private double y;
     
  public void setPt(double x, double y) {
      this.x = x;
      this.y = y;
  }
 
// Now this method should take another vertex and return their distance. The formula itself is OK.

  public double distance(Vertex otherPoint) {
      return Math.sqrt(((this.x - otherPoint.x)*(this.x - otherPoint.x)) + ((this.y - otherPoint.y)*(this.y - otherPoint.y)));
  }
}

Vertex a = new Vertex();
Vertex b = new Vertex();
a.setPt(1,1);
b.setPt(0,0);
b.distance(a); // This call does not calculate the distance.
System.out.println("Distance is: " + b);

---

What am I doing wrong?

Where is your main method?

Also you should ALWAYS post error message.

Oh, sorry. The main method is just the code on the 18-23 lines.

Code:

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public static void main(String[] args) { 
        Vertex a = new Vertex();
        Vertex b = new Vertex();
        a.setPt(1,1);
        b.setPt(0,0);
        b.distance(a)
        System.out.println("Distance is: " + b);
}

---

And there is no error, it just writes "Distance is: [0.0, 0.0]", which I dont really get either...

You want the distance between first and second number correcT?

Well, I want the distance between two 2D points described with two coordinates. The formula is distance = sqrt( (x2-x1)^2 + (y2-y1)^2) ).
So, for my two vertices (a, b) it should be sqrt(2).

First of all your instance variables x and y are private, which means you need to make some kind of geters and seters for them(and access them through those geters. Instead of this.x - otherPoint.x there should be this.x - otherPoint.getX()). Or easier (but more dirty) way is to make your variables public. Secondly you are printing out your vertex object b not the distance between 2 vertex objects a and b.

Quote:

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Originally Posted by dawnMist

Well, I want the distance between two 2D points described with two coordinates. The formula is distance = sqrt( (x2-x1)^2 + (y2-y1)^2) ).
So, for my two vertices (a, b) it should be sqrt(2).

---

Ok, that confused me. I thought you just wanted the distance between one number and another.
Sadly i am of no help then.

Code:

---


b.distance(a); // delete this line
System.out.println("Distance is: " + b.distance(a));

---

I'm no expert, but I think this is the change you require.

Thank you both, that was the exact problem.
I have advanced and another problem occured.

Code:

---

public class Vertex
{
  private double x;
  private double y;
     
  public void setX(double x) {
      this.x = x;
  }
 
  public void setY(double y) {
      this.y = y;
  }
   
  public double getX() {
      return x;
  }

  public double getY() {
      return y; 
  }
}

public class Triangle
{
    private double ax;
    private double ay;
    private double bx;
    private double by;
    private double cx;
    private double cy;
   
    private double distance1;
    private double distance2;
    private double distance3;
   
    private Vertex a = new Vertex();
    private Vertex b = new Vertex();
    private Vertex c = new Vertex();
   
    public void setA(Vertex v) {
        this.ax = vert.getX();
        this.ay = vert.getY();
    }
   
    public void setB(Vertex v) {
        this.bx = vert.getX();
        this.by = vert.getY();
    }
   
    public void setC(Vertex v) {
        this.cx = vert.getX();
        this.cy = vert.getY();
    }
   
    public Vertex getA() {
        return a;
    }
   
    public Vertex getB() {
        return b;
    }
   
    public Vertex getC() {
        return c;
    }
}

public static void main(String[] args) {
       
        Triangle t = new Triangle();       
               
        Vertex a = new Vertex();
        Vertex b = new Vertex();
        Vertex c = new Vertex();
       
        t.setA(a.getX,a.getY); // There is the error: "cannot find symbol - variable getX"
        // t.setA(0.0,0.0); -this doesnt work either
}

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Where is the problem?

You have to write

Code:

---

t.setA(a.getX(), a.getY());

---

because getX() and getY() are methods.

Quote:

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Originally Posted by achill

You have to write

Code:

---

t.setA(a.getX(), a.getY());

---

because getX() and getY() are methods.

---

Yes, of course. But I still get this error: "setA cannot be applied to (double, double)" or "getX cannot be applied to (double, double)"

The setter takes a Vertex, not two doubles.
The getter (inderstandably) takes no parameters.

Ah okay, my fault.
The method setA() wants something of the type Vertex. So just write

Code:

---

t.setA(a);

---

Ok. And when I want to set vertex using Triangle? I mean specific values now...

this way:

Code:

---

Vertex a = new Vertex();
a.setX(1.0);
a.setY(2.0);
t.setA(a);

---

or you write a constructor for the class Vertex that takes the values for x and y. So you can write simply:

Code:

---

t.setA(new Vertex(1.0, 2.0));

---

(code is untested!)

Quote:

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Originally Posted by s3ib

First of all your instance variables x and y are private, which means you need to make some kind of geters and seters for them(and access them through those geters. Instead of this.x - otherPoint.x there should be this.x - otherPoint.getX()). Or easier (but more dirty) way is to make your variables public.

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The code is in the Vertex class. Hence it can access private members of any instance of the class.

db