How to return different values toString?

Royce Roy162705-Nov-2014

I'm pretty new in java and I'm doing a simple program but I don't know why I get different values, i.e., if I use getX, getY and getZ I get (6,5,8) but if I use toString I get different values for X and Y (3, 4, 8), so can anyone explain me why it happens because as far as I understand it should get the same values in both cases or what I'm doing wrong?

publicclassCoordinates {
 
    privatedouble coorX, coorY;
 
    Coordinates()
    {
        coorX = 1;
        coorY = 1;
    }
 
    Coordinates(double x, double y)
    {
        coorX = x;
        coorY = y;      
    }
 
    void setX(double x)
    {
        coorX = x; 
    }
 
    void setY(double y)
    {
        coorY = y; 
    }
 
    double getX()
    {
        return coorX;
    }
 
    double getY()
    {
        return coorY;
    }
 
    publicString toString()
    {
        String myString = "(" + coorX + " , " + coorY + ")";
        return myString;
    }
 
    publicclassCoordinates3D extends Coordinates{
        privatedouble coorZ;
 
        Coordinates3D()
        {
            super();
            coorZ = 1;
        }
 
        Coordinates3D(double x, double y, double z)
        {
            super(x,y);
            coorZ = z;
        }
 
        publicvoid setZ(double z)
        {
            coorZ = z;
        }
 
        double getZ()
        {
            return coorZ;
        }
 
        @Override
        publicString toString()
        {
            String myString = "(" + coorX + " , " + coorY + " , " + coorZ + ")" ;
            return myString;
 
        }
 
    }
 
 
    /**
     * @param args
     */
    publicstaticvoid main(String[] args) {
        // TODO Auto-generated method stub
 
        Coordinates test1 = newCoordinates(3,4);
 
 
        System.out.println(test1.toString());
 
        System.out.println(test1.getX());
        System.out.println(test1.getY());
 
 
        Coordinates3D test2 = test1.newCoordinates3D(6,5,8);
 
        System.out.println(test2.toString()); ---> here is the problem
 
        System.out.println(test2.getX());
        System.out.println(test2.getY());
        System.out.println(test2.getZ());
 
 
    }
 
}

java

Updated on 05-Nov-2014

classCoordinates{privatedouble coorX, coorY;}publicclassCoordinates3DextendsCoordinates{@OverridepublicString toString(){String myString ="("+ coorX +" , "+ coorY +" , "+ coorZ +")";return myString;}}

Can you answer this question?

Answer

1 Answers

Takeshi Okada

05-Nov-2014

First, there is a problem on how you define the visibility of the fields of the super class:

publicclassCoordinates{privatedouble coorX, coorY;

This is that you cannot invoke super.coorX nor super.coorY on any subclass e.g. Coordinates3D. So, in toString method, when you have this code:

String myString ="("+ coorX +" , "+ coorY +" , "+ coorZ +")";

It compiles and runs fine because Coordinates3D is an inner class. So, when using coorX here it's accessing to the value of coorX field stored in the instance of Coordinates class that created the instance of Coordinates3D. This can be easy to replicate if you separate the classes:

The best solution would be:

mark the fields in the super class as protected
separate the classes

If you still want to keep Coordinates3D as inner class (not recommended), then:

mark the fields in the super class as protected
use super.coorX and super.coorY to not have the same unexpected behavior.

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How to return different values toString?

Royce Roy

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