Hi everyone, I was writing a program to show visually some vectors I was implementing with Java but I ran into an issue. My program has 3 classes, a driver, a Vector class and a VectorDisplay. The driver and vector class are self explanatory, but here is the code.
Driver:

import phys.*;
import java.util.*;

public class Driver
{
    public static Vector1 vect1 = new Vector1(50, 70);

    public static void dispVectStats()
    {
        vect1.dispVect();
        vect1.drawVect();
    }

    public static void main(String[] args)
    {
        System.out.print("\f");
        dispVectStats();
    }
}

Vector:

package phys;

import java.util.*;


public class Vector1
{
    private int x;
    private int y;

    public Vector1(int xTemp, int yTemp)
    {
        x = xTemp;
        y = yTemp;
    }

    public void drawVect()
    {
        VectorGraph vgraph = new VectorGraph(x, y);
        vgraph.init();
        vgraph.repaint();
    }

    public void dispVect()
    {
        System.out.print("X: " + x + "\n");
        System.out.print("Y: " + y + "\n");
    }
}
`

Vector Display:

package phys;
import java.awt.*;
import javax.swing.*;
import java.util.*;

public class VectorGraph extends JPanel
{
    private int xLength = 500;
    private int yLength = 500;

    private int xi1 = xLength/2;
    private int yi1 = yLength/2;
    private int xf1;
    private int yf1;

    public VectorGraph()
    {
        super();
    }

    public VectorGraph(int xF, int yF)
    {
        super();
        xf1 = xF;
        yf1 = yF;
    }


    public void paint(Graphics g)
    {
        super.paint(g);
        g.drawLine(0, yLength/2, xLength, yLength/2); 
        g.drawLine(xLength/2, 0, xLength/2, yLength); 
        g.drawLine(xi1, yi1, xf1, yf1); 
        System.out.print(xf1);
    }

    public void init()
    {
        JFrame frame = new JFrame("Vectors");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(xLength, yLength);

        VectorGraph panel = new VectorGraph();
        frame.setContentPane(panel);          
        frame.setVisible(true);  
    }
}

When I run the driver the code executes with no errors and it draws a line on the JFrame from 250 to 0 meaning that xf1 and yf1 are both 0 when the paint code is run (Also evidenced in the trace command which outputs 0) but in the constructor I set xf1 and yf1 to 50 and 70. What is happening that xf1 and yf1 both are resetting to 0?

Thanks for any help in advance.

It's line 44 that's worng.
When you init your VectorGraph instead of adding that VectorGraph to the JFrame you create a second VectorGraph (with default values of 0) and add that instead. Your correctly constructed VectorGraph never gets displayed.

Edited 4 Years Ago by JamesCherrill

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