Using JScrollBar to update Components

Question

public class FaceMain extends JFrame {
CreateFace p1 = new CreateFace();
private ControlPanel panel;

public FaceMain(ControlPanel value) {
panel = value;
    JFrame main = new JFrame();
    main.setTitle("Face Frame");
    main.setSize(new Dimension(600, 600));
    main.setLocationRelativeTo(null);
    main.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    main.setVisible(true);

    Container c = main.getContentPane();
    main.add(p1);
    panel.eyesSetE(true);
    JFrame control = new JFrame();
    control.setTitle("Control Panel");
    control.setSize(new Dimension(300, 300));
    control.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    control.setLocationRelativeTo(main);
    control.setVisible(true);

    ControlPanel p2 = new ControlPanel(p1);
    control.add(p2);

}
}

public class ControlPanel extends JPanel {
boolean eyesSetEdit = false, faceSetEdit = false, mouthSetEdit = false,
        editEyes;
private Color purple = new Color(133, 22, 145);
private CreateFace face;
private CreateFace p1;

public ControlPanel(CreateFace value) {
    face = value;
    p1 = value;
    setLayout(new GridLayout(4, 0));
    JButton change = new JButton("Click");
    add(change);
    JLabel info = new JLabel("Click Above To Change Features",
            JLabel.CENTER);
    add(info);
    JLabel info1 = new JLabel("Slide Below To Change Size", JLabel.CENTER);
    add(info1);
    JScrollBar slider = new JScrollBar(Scrollbar.HORIZONTAL, 0, 100, 0, 300);
    add(slider);
public void eyesSetE(boolean x) {
    eyesSetEdit = x;
}

public boolean getEyesSet() {
    return eyesSetEdit;
}

I have expanded my class to try and change a boolean value which will be used exstensivly in the ControlPanel class to make decisions however everytime I start the program I get a nullpointerexception at the line "panel.eyesSetE(true);" Even if I try and call getEyesSet() I still recieve a nullpointer

Answer 1

You never change the instance of circle within the CreateCircle class, so it never changes size.

Don't use static for what should be an instance variable, instead make use of the instance of the class you created and provide a setter method to change the variable...

Basically, this example passes the instance of p1 to the ControlPanel pane so that it has some context by which to manipulate what you have previously created.

import datetest.CircleShort.ControlPanel;
import datetest.CircleShort.CreateCircle;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.Scrollbar;
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;
import java.awt.geom.Ellipse2D;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JScrollBar;

public class CircleShort extends JFrame {

    CreateCircle p1 = new CreateCircle();

    public CircleShort() {
        CreateCircle p1 = new CreateCircle();
        JFrame main = new JFrame();
        main.setSize(new Dimension(600, 600));
        main.setLocationRelativeTo(null);
        main.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        main.setVisible(true);

        Container c = main.getContentPane();
        main.add(p1);
        JFrame control = new JFrame();
        control.setTitle("Control Panel");
        control.setSize(new Dimension(300, 300));
        control.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        control.setLocationRelativeTo(main);
        control.setVisible(true);

        ControlPanel p2 = new ControlPanel(p1);
        control.add(p2);

    }

    static class CreateCircle extends JComponent {

        int circleX = 100;
        Ellipse2D.Double circle;

        public CreateCircle() {
            circle = new Ellipse2D.Double(circleX, 50, 400, 350);
        }

        public void setCircleX(int x) {
            circleX = x;
            circle = new Ellipse2D.Double(circleX, 50, 400, 350);
            repaint();
        }

        public int getCircleX() {
            return circleX;
        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2 = (Graphics2D) g;
            g2.setColor(Color.red);
            g2.fill(circle);
        }
    }

    class ControlPanel extends JComponent {

        private CreateCircle circle;

        public ControlPanel(CreateCircle value) {
            circle = value;
            setLayout(new GridLayout(4, 0));
            JButton change = new JButton("Click");
            add(change);
            JLabel info = new JLabel("Click Above To Change Color",
                    JLabel.CENTER);
            add(info);
            JLabel info1 = new JLabel("Slide Below To Change Size",
                    JLabel.CENTER);
            add(info1);
            JScrollBar slider = new JScrollBar(Scrollbar.HORIZONTAL, 0, 100, 0,
                    300);
            add(slider);
            slider.addAdjustmentListener(new AdjustmentListener() {

                public void adjustmentValueChanged(AdjustmentEvent e) {
                    System.out.println(e.getValue());
                    circle.setCircleX((circle.getCircleX() + (e.getValue() % 5)));
                }

            });

        }
    }

    static class CircleRun {

        public static void main(String[] args) {
            new CircleShort();
        }
    }
}

static is evil until you truly understand how to use it. If you find yourself making some field or method static just because you can't seem to figure out how to access it, then you are likely doing something wrong, be careful with it...

The next question this actually raises is, "why?"

A JSlider would be a more appropriate control to use and would be conceptually easier for a user to understand