通过单击鼠标按钮绘制和存储对象

Question

I am trying to draw circle objects with each click and then store every circle object into an Arraylist, I don't know why my program is not working! If I removed the arraylist and the line that create a new circle object, the program will work. How would I make my program store all circuit objects into an Arraylist ?

 import javax.swing.JPanel;
    import java.awt.Color;
    import java.awt.Graphics;
    import java.awt.event.MouseAdapter;
    import java.awt.event.MouseEvent;
    import java.util.ArrayList;
    import java.util.Random;

    public class CircleObj extends JPanel {
        private int rColor;
        private int gColor;
        private int bColor;
        private int radius;
        private Random rand = new Random();
        private int xStart;
        private int yStart;
        ArrayList <Circle> xxx ;

        public CircleObj () {
        xxx =  new ArrayList<Circle>();

        addMouseListener(new MouseAdapter() {

            public void mouseClicked (MouseEvent e) {

            xStart = e.getX();
            yStart = e.getY();
            rColor = rand.nextInt(256);
            gColor = rand.nextInt(256);
            bColor = rand.nextInt(256);
            radius = rand.nextInt(20);


            repaint();
            }
        }); // end addMouseListener
        }

        public void paintComponent (Graphics g) {
        super.paintComponent(g);
        g.setColor(new Color(rColor, gColor, bColor));
        g.fillOval(xStart, yStart, radius, radius);
        xxx.add(new Circle());
        }

        private class Circle {
            private int x;
            private int y;
            private int r;
            private int rcol;
            private int gcol;
            private int bcol;

            public Circle()
                {
                x=xStart;
                y=yStart;
                r=radius;
                rcol= rColor;
                gcol= gColor;
                bcol= bColor;

                }




        }

    }

======

import javax.swing.JFrame;
import java.awt.BorderLayout;

public class HW3 {
    public static void main (String[] arg) {
    JFrame frame = new JFrame("Circles");
    CircleObj canvas = new CircleObj();

    frame.add(canvas, BorderLayout.CENTER);
    frame.setBounds(250, 98, 600, 480);
    //frame.setLayout(new BorderLayout());
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
    } // end main
} //end HW3

Answer 1

Don't add the new shape inside the paintComponent method, paintComponent can be called for any number of reasons, many of which you don't control, instead, create it when the mouseClicked event is triggered...

public void mouseClicked (MouseEvent e) {

    xStart = e.getX();
    yStart = e.getY();
    rColor = rand.nextInt(256);
    gColor = rand.nextInt(256);
    bColor = rand.nextInt(256);
    radius = rand.nextInt(20);

    xxx.add(new Circle(xStart, yStart, new Color(rColor, gColor, bColor), radius));

    repaint();
}

And then in your paintComponent , loop through the ArrayList and paint the circles...

public void paintComponent (Graphics g) {
    super.paintComponent(g);
    for (Circle c : xxx) {
        g.setColor(c.getColor());
        g.fillOval(c.getX(), c.getY(), c.getRadius(), c.getRadius());
    }
}

Now, you're going to have to modify you Circle class to provide getters which the CircleObj can use in order to actually paint the circles...

Alternatively, you could make use of the Shape s API provided within Java...Have a look at Working with Geometry for more details...