如何使用数组做随机圆

Question

我一直在做一个学校作业，老师想让我们在JPanel上出现7个圆圈，然后向下移动。一旦一个圆到达底部，就应该创建一个新的圆来替换到达JPanel底部的圆。我决定用一个数组继续做随机圈，但我不能让它正常工作。我使用for循环用半径和颜色随机的圆填充数组。代码可以编译，但当我运行它时，我得到一个异常。我很难让阵列正常工作。我不确定的另一件事是如何绘制圆圈，以便它们在JPanel中有空间。

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.Random;

public class keyExample extends JPanel implements ActionListener, KeyListener {

    private Circle[] circles = new Circle[7];

    Timer t = new Timer(5, this);
//current x and y
    double x = 150, y = 200;
    double changeX = 0, changeY = 0;
    private Circle;
    private int circlex = 0, circley = 0; // makes initial starting point of circles 0
    private javax.swing.Timer timer2;

    public keyExample() {

        t.start();
        addKeyListener(this);
        setFocusable(true);
        setFocusTraversalKeysEnabled(false);


        }

        timer2 = new javax.swing.Timer(33, new MoveListener());
        timer2.start();

    }

    public void NewCircle() {
        Random colors = new Random();
        Color color = new Color(colors.nextInt(256), colors.nextInt(256), colors.nextInt(256));

        Random num = new Random();
        int radius = num.nextInt(45);

        for (int i = 0; i < circles.length; i++) {
            circles[i] = new Circle(circlex, circley, radius, color);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        g2.setColor(Color.BLUE);
        g2.fill(new Rectangle2D.Double(x, y, 40, 40));
        NewCircle();
        for (int i = 0; i < circles.length; i++)
        circles[i].fill(g);

    }

    public void actionPerformed(ActionEvent e) {
        repaint();
        x += changeX;
        y += changeY;
        changeX = 0;
        changeY = 0;

    }

    public void up() {
        if (y != 0) {
            changeY = -3.5;
            changeX = 0;
        }
    }

    public void down() {
        if (y <= 350) {
            changeY = 3.5;
            changeX = 0;

        }
    }

    public void left() {
        if (x >= 0) {
            changeX = -3.5;
            changeY = 0;
        }
    }

    public void right() {
        if (x <= 550) {
            changeX = 3.5;
            changeY = 0;
        }
    }

    private class MoveListener implements ActionListener {

        public void actionPerformed(ActionEvent e) {

            repaint();
            Random speed = new Random();
            int s = speed.nextInt(8);
            circle.move(0, s);
        }
    }

    public void keyPressed(KeyEvent e) {
        int code = e.getKeyCode();
        if (code == KeyEvent.VK_UP) {
            up();
        }
        if (code == KeyEvent.VK_DOWN) {
            down();
        }
        if (code == KeyEvent.VK_RIGHT) {
            right();
        }
        if (code == KeyEvent.VK_LEFT) {
            left();
        }
    }

    public void keyTyped(KeyEvent e) {
    }

    public void keyReleased(KeyEvent e) {
    }
}

Answer 1

你的问题是你试图用circle变量来绘制，这个变量你从来没有为它分配过有效的引用。

一个解决方案是通过Circle=new Circle(...)给它一个有效的引用，但是话虽如此，我还是告诉您忽略它，因为您甚至不应该使用变量Circle。把它处理掉就行了。您要做的是使用circles数组--这是您应该在paintComponent方法中绘制的内容。在paintComponent中使用一个for循环，并遍历数组，绘制数组中包含的每个循环项。