CODEWITHSUNDEEP
javainheritancepolymorphism
Sam
Sam

Reputation: 365

Unexpected output NULL

I'm working with inheritance and polymorphism. I'm getting only this output instead of displaying the required points.

But printing points alone works properly. Printing lines creates problem.

Output: line joining null null

package serial;

import java.io.*;

class Point
{
    private int x,y;
    Point(int x,int y)
    {
        this.x = x;
        this.y = y;
    }
    int getX()
    {
        return x;
    }
    int getY()
    {
        return y;
    }
    void setX(int x)
    {
        this.x = x;
    }
    void setY(int y)
    {
        this.y = y;
    }
    public String toString()
    {

        //String s = "Points joining line are ("+p1.getX()+","+p1.getY()+") and ("+p2.getX()+","+p2.getY()+")";     
        return "(" + x + "," + y + ")"; 
    }
}

class Line 
{
    private Point p1, p2;
    Line()
    {

    }
    Line(Point p1, Point p2)
    {
        p1 = new Point(2,2);
        p2 = new Point(3,3);
    }
    void setP1(Point p1)
    {
        p1.setX(2);
        p1.setY(2);
    }
    Point getP1()
    {
        return p1;
    }
    void setP2(Point p2)
    {
        p2.setX(3);
        p2.setY(3);
    }
    Point getP2()
    {
        return p2;
    }
    public String toString()
    {
        String str;
        str = "line joining "+this.p1+" "+this.p2+"";
        return str;     

    }
}
public class chumma {
    public static void main(String args[])
    {
        Point p1 = new Point(2,2);
        Point p2 = new Point(3,3);
        Line l1 = new Line(p1,p2);
        //l1.setP1(p1);
        //l1.setP2(p2); 
        System.out.println(l1);

    }

}

Upvotes: 0

Views: 55

Answers (2)

A4L
A4L

Reputation: 17595

Your consturctor should look like this:

Line(Point p1, Point p2)
{
    this.p1 = p1;
    this.p2 = p2;
}

The mistake is that you are not assigning the member variables but the parameter which are hiding your member variables.

Use the this keyword to explicitly address the members of a class.

Upvotes: 0

rgettman
rgettman

Reputation: 178263

Your constructor reassigns the local references p1 and p2 instead of assigning the instance variables. Because the instance variables are not assigned, Java gives them a default value of null.

Add this. to refer to the instance variables.

 Line(Point p1, Point p2)
 {
     this.p1 = p1;
     this.p2 = p2;
 }

You'll also want to assign something to those variables in your no-arg constructor.

Upvotes: 5

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