Java GUI-从抽象类调用draw方法

Question

My compiled program runs with no errors but when I click inside the canvas no shapes are generated/painted. compiled program PaintComponent Class

private class CanvasPanel extends JPanel {

  //this method draws all shapes 
  public void paintComponent(Graphics page)
   {
        super.paintComponent(page);
        setBackground(Color.WHITE);

        for (int i = 0; i < shapeList.size(); i++) {
            ((Shape) shapeList.get(i)).draw(page);
        }
   }     
} 

Pointer listener class.

public class PointListener implements MouseListener
    {
     public void mousePressed (MouseEvent event)
      {
         Point pt = event.getPoint();
         //pointList.add(event.getPoint());
         if (currentShape.equals("circle")) {
             nShape = new Circle((int)pt.getX(), (int)pt.getY(), currentSize, currentSize, currentColor);
             shapeList.add(nShape);
         } else {
             nShape = new Square((int)pt.getX(), (int)pt.getY(), currentSize, currentSize, currentColor);
             shapeList.add(nShape);
         }
         repaint(); 
      }

Abstract Shape class

public abstract class Shape {

    protected int x;
    protected int y;
    protected int width;
    protected int height;
    protected Color color;

    public Shape (int x1, int y1, int width, int height, Color color) {
        this.x = x1;
        this.y = y1;
        this.width = width;
        this.height = height;

    }

    public void draw (Graphics page) {
    }
}

So ideally the user clicks on the canvas with their selected options, the click generates the shape object and stores in a list. The paint component cycles through the whole list and calls the shape class draw method which pulls from my Square/Circle child classes and draws their selected shape. Unfortunately nothing is happening. Is something missing? Thanks!

Here is a repo containing all of my project. https://github.com/Purpleshoes/assignment7

Answer 1

I went through with your WholePanel class and found below issues

1. You created ComboListener class and never used that , it should use like this comboShapes.addActionListener(new ComboListener());

2. You created PointListener class and never used that , it should use like this canvas.addMouseListener(new PointListener());

3. You used local JComboBox instances instead of class level JComboBox instances , therefore actionPerformed() method in ComboListener class will never work

4. actionPerformed method in ButtonListener class , doesn't make any sense , so u need to re-do the logic

Therefore i made few changes to WholePanel class , see below

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.util.ArrayList;

public class WholePanel extends JPanel {

    private Color currentColor = Color.black;
    private CanvasPanel canvas;
    private JPanel topPanel;
    private JButton undo;
    private ArrayList shapeList;
    int flag = 1; //Debug
    private String currentShape = "circle";
    private int currentSize = 10;

    private ArrayList pointList;

    Shape nShape;

    JComboBox<String> comboShapes = new JComboBox<String>();
    JComboBox<Integer> comboSize = new JComboBox<Integer>();
    JComboBox<String> comboColors = new JComboBox<String>();

    public WholePanel() {
        currentColor = Color.black;
        shapeList = new ArrayList();
        pointList = new ArrayList();

        topPanel = new JPanel();

        canvas = new CanvasPanel();
        canvas.addMouseListener(new PointListener());

        JSplitPane sp = new JSplitPane(JSplitPane.VERTICAL_SPLIT, topPanel, canvas);

        setLayout(new BorderLayout());
        add(sp);

        undo = new JButton("Undo");

        comboShapes = new JComboBox<String>();
        comboShapes.addItem("circle");
        comboShapes.addItem("square");
        comboShapes.addActionListener(new ComboListener());

        comboSize = new JComboBox<Integer>();
        comboSize.addItem(10);
        comboSize.addItem(20);
        comboSize.addItem(30);
        comboSize.addItem(40);
        comboSize.addItem(50);
        comboSize.addActionListener(new ComboListener());

        comboColors = new JComboBox<String>();
        comboColors.addItem("Black");
        comboColors.addItem("Red");
        comboColors.addItem("Blue");
        comboColors.addItem("Green");
        comboColors.addItem("Orange");
        comboColors.addActionListener(new ComboListener());

        topPanel.add(comboShapes, BorderLayout.WEST);
        topPanel.add(comboSize, BorderLayout.CENTER);
        topPanel.add(comboColors, BorderLayout.EAST);
        topPanel.add(undo, BorderLayout.EAST);
    }

    private class CanvasPanel extends JPanel {

        //this method draws all shapes 
        public void paintComponent(Graphics page) {
            super.paintComponent(page);
            setBackground(Color.WHITE);

//            page.setColor(nShape.color);
//            page.drawOval(nShape.x, nShape.y, nShape.width, nShape.height);
//            page.fillOval(nShape.x, nShape.y, nShape.width, nShape.height);
            for (int i = 0; i < shapeList.size(); i++) {
                //Point drawPoint = (Point) pointList.get(i);
                ((Shape) shapeList.get(i)).draw(page);
            }
        }

        @Override
        public void paint(Graphics g) {

            super.paint(g);
            setBackground(Color.WHITE);

            //page.setColor(nShape.color);
            //page.drawOval(nShape.x, nShape.y, nShape.width, nShape.height);
            //page.fillOval(nShape.x, nShape.y, nShape.width, nShape.height);
            for (int i = 0; i < shapeList.size(); i++) {
                //Point drawPoint = (Point) pointList.get(i);
                ((Shape) shapeList.get(i)).draw(g);
            }

        }

    }

    private class ButtonListener implements ActionListener {

        public void actionPerformed(ActionEvent event) {
            undo = new JButton("Undo");
            undo.addActionListener(new ButtonListener());
        }
    } // end of ButtonListener

    // listener class to set the color chosen by a user using
    // color combo box, set the size chosen using size combo box
    // or set the shape (circle or square) using shape combo box
    private class ComboListener implements ActionListener {

        public void actionPerformed(ActionEvent event) {
            System.out.println("action action");
            if (event.getSource() == comboShapes) {
                currentShape = (String) comboShapes.getSelectedItem();
            }

            if (event.getSource() == comboSize) {
                currentSize = (int) comboSize.getSelectedItem();
            }

            if (event.getSource() == comboColors) {
                currentColor = Color.getColor((String) comboColors.getSelectedItem());
            }
        }
    } // end of ComboListener

    // listener class that listens to the mouse
    public class PointListener implements MouseListener {

        public void mousePressed(MouseEvent event) {
            Point pt = event.getPoint();
            //pointList.add(event.getPoint());
            if (currentShape.equals("circle")) {
                nShape = new Circle((int) pt.getX(), (int) pt.getY(), currentSize, currentSize, currentColor);
                shapeList.add(nShape);
            } else {
                nShape = new Square((int) pt.getX(), (int) pt.getY(), currentSize, currentSize, currentColor);
                shapeList.add(nShape);
            }
            repaint();
        }

        public void mouseReleased(MouseEvent event) {
        }

        public void mouseClicked(MouseEvent event) {
        }

        public void mouseEntered(MouseEvent event) {
        }

        public void mouseExited(MouseEvent event) {
        }

    } // end of PointListener

} // end of Whole Panel Class