Question

我创建了一个应用程序，它使用JPanel和JFrame绘制随机数量的椭圆（具有随机大小和颜色）。一切似乎都是正确的......但是当我执行代码时，没有绘制椭圆。我只收到一个空白屏幕（JFrame出现，但只是空白）。

它有3个类：MyOval，DrawPanel和DrawTest。

MyOval Class

package drawingovals;

import java.awt.Color;
import java.awt.Graphics;

public class MyOval {
    private int x1;
    private int y1;
    private int x2;
    private int y2;
    private Color myColor;
    private boolean isFilled;

    public MyOval(int x1, int y1, int x2, int y2, Color color, boolean isFilled) {
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.x2 = x2;
        myColor = color;
        this.isFilled = isFilled;
    }

    public int getUpperLeftX(){
        return x1;
    }

    public int getUpperLeftY(){
        return y1;
    }

    public int getWidth(){
        return x2 - x1;
    }

    public int getHeight() {
        return y2 - y1;
    }

    public String getColor() {
        return myColor.toString();
    }

    public boolean getFilling(){
        return isFilled;
    }

    public void setUpperLeftX(int value) {
        x1 = value;
    }

    public void setUpperLeftY(int value) {
        y1 = value;
    }

    public void setDownRightX(int value) {
        x2 = value;
    }

    public void setDownRightY(int value) {
        y2 = value;
    }

    public void drawNoFill(Graphics g) {
        g.setColor(myColor);
        g.drawOval(getUpperLeftX(), getUpperLeftY(), getWidth(), getHeight());
    }

    public void drawFill(Graphics g) {
        g.setColor(myColor);
        g.fillOval(getUpperLeftX(), getUpperLeftY(), getWidth(), getHeight());
    }
}

DrawPanel类

package drawingovals;

import java.awt.Color;
import java.awt.Graphics;
import java.util.Random;
import javax.swing.JPanel;

public class DrawPanel extends JPanel{
    private Random randomNumbers = new Random();
    private MyOval[] ovals;

    public DrawPanel() {
        setBackground(Color.WHITE);

        ovals = new MyOval[5 + randomNumbers.nextInt(5)];

        for (int count = 0; count < ovals.length; count++) {
            int x1 = randomNumbers.nextInt(300);
            int y1 = randomNumbers.nextInt(300);
            int x2 = randomNumbers.nextInt(300);
            int y2 = randomNumbers.nextInt(300);

            Color color = new Color(randomNumbers.nextInt(256),
                    randomNumbers.nextInt(256), randomNumbers.nextInt(256));

            boolean fill = randomNumbers.nextBoolean();

            ovals[count] = new MyOval(x1, y1, x2, y2, color, fill);
        }
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (int count = 0; count < ovals.length - 1; count++) {
            ovals[count].drawFill(g);
        }
    }
}

DrawTest Class

package drawingovals;

import javax.swing.JFrame;

public class DrawTest {

    public static void main(String[] args) {
        DrawPanel panel = new DrawPanel();
        JFrame application = new JFrame();

        application.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        application.add(panel);
        application.setSize(400, 400);
        application.setVisible(true);
    }

}

Answer 1

您需要注意您的椭圆形高度和宽度仅包含正值 - 您的代码不会这样做。在获取椭圆属性时，请考虑使用Math.max，Math.min或Math.abs来帮助您实现此目的。

另外，这是错误的，因为您正在重复设置x2错误忽略y2：

    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;  // *** these are the same
    this.x2 = x2;  // *** these are the same

这样的事情会起作用：

public MyOval(int x1, int y1, int x2, int y2, Color color, boolean isFilled) {
    this.x1 = Math.min(x1, x2);
    this.y1 = Math.min(y1, y2);
    this.x2 = Math.max(x1, x2);
    this.y2 = Math.max(y1, y2);;
    myColor = color;
    this.isFilled = isFilled;
}

将来，解决这些类型问题的关键是使用调试器检查程序的字段，这里是程序运行时的椭圆属性，然后看看它们是否有意义，然后为什么。

绘制椭圆形的JPanel问题

1 个答案: