Graphics2D绘制不正确，它只是椭圆的绘制部分

Question

我正在尝试使用Graphics2D在JFrame上绘制一个椭圆，我希望它使用窗口的大小进行调整，从技术上讲，它只是不绘制椭圆的第3个。这绝对是我做错的事情，我是Java的Graphics2D部分的新手。

我不确定这是否是我的计算机，所以我尝试在另一台PC上运行我的代码以使其再次发生，所以我不确定哪里出了问题。

import javax.swing.*;
import java.awt.*;

public class ClockViewer {
    public static void main(String[] args) {
        //create frame
        JFrame frame = new JFrame();
        final int Frame_Width = 110;
        final int Frame_Height = 130;

        //set frame attributes
        frame.setSize(Frame_Width, Frame_Height);
        frame.setTitle("A Really Descriptive Title...");
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //get pane attributes
        System.out.println(frame.getContentPane().getWidth());
        System.out.println(frame.getContentPane().getHeight());

        //create ellipse
        EllipseComponent ellipse = new EllipseComponent();

        //add ellipse to frame
        while(frame.getContentPane().getHeight() > 0 && frame.getContentPane().getWidth() > 0) {
            int posX = Math.round(frame.getContentPane().getWidth() / 100) * 20;
            int posY = Math.round(frame.getContentPane().getHeight() / 100) * 20;
            int Width = Math.round(frame.getContentPane().getWidth() / 100) * 80;
            int Height = Math.round(frame.getContentPane().getHeight() / 100) * 80;
            ellipse.setAll(posX, posY, Width, Height);
            frame.add(ellipse);
        }
    }
}

这是下一个文件：

import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;

public class EllipseComponent extends JComponent {
    //global variables for ellipse drawing
    int posX = 0;
    int posY = 0;
    int Width = 0;
    int Height = 0;

    //getters for getting variables values
    public int getPosX() {
    return this.posX;
    }
    public int getPosY() {
        return this.posY;
    }
    @Override
    public int getWidth() {
        return this.Width;
    }
    @Override
    public int getHeight() {
        return this.Height;
    }

    //setters for setting variable values
    public void setPosX(int newPosX) {
        this.posX = newPosX;
    }
    public void setPosY(int newPosY) {
        this.posY = newPosY;
    }
    public void setWidth(int newWidth) {
        this.Width = newWidth;
    }
    public void setHeight(int newHeight) {
        this.Height = newHeight;
    }

    //setter for all variables
    public void setAll(int newPosX, int newPosY, int newWidth, int newHeight) {
        this.posX = newPosX;
        this.posY = newPosY;
        this.Width = newWidth;
        this.Height = newHeight;
    }

    //paint ellipse using graphics
    @Override
    public void paint(Graphics g) {
        Graphics g2 = (Graphics2D) g;
        g2.drawOval(posX, posY, Width, Height);
    }
}

感谢大家提供的任何帮助^^

编辑：如果有帮助，我会得到这些错误：

Exception in thread "AWT-EventQueue-0" java.lang.ArrayIndexOutOfBoundsException: No such child: 0

at java.awt.Container.getComponent(Container.java:336)

at javax.swing.JComponent.rectangleIsObscured(JComponent.java:4390)

at javax.swing.JComponent.paint(JComponent.java:1054)

at javax.swing.JComponent.paintToOffscreen(JComponent.java:5210)

at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1579)

at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1502)

at javax.swing.RepaintManager.paint(RepaintManager.java:1272)

at javax.swing.JComponent._paintImmediately(JComponent.java:5158)

at javax.swing.JComponent.paintImmediately(JComponent.java:4969)

at javax.swing.RepaintManager$4.run(RepaintManager.java:831)

at javax.swing.RepaintManager$4.run(RepaintManager.java:814)

at java.security.AccessController.doPrivileged(Native Method)

at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)

at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:814)

at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:789)

at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:738)

at javax.swing.RepaintManager.access$1200(RepaintManager.java:64)

at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1732)

at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)

at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)

at java.awt.EventQueue.access$500(EventQueue.java:97)

at java.awt.EventQueue$3.run(EventQueue.java:709)

at java.awt.EventQueue$3.run(EventQueue.java:703)

at java.security.AccessController.doPrivileged(Native Method)

at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)

at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)

at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)

at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)

at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)

at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)

at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

Answer 1

我没有得到您得到的错误。但是，这不是在Swing中进行自定义绘画的正确方法。我建议您看一下how to perform custom painting。长话短说，尽管您尝试在while条件下执行的操作无效。相反，让组件根据其父对象的大小和坐标进行绘制，而不必显式设置它们：

/**
 * @Overide paint method was a thing in AWT.
 * In Swing you must override paintComponent (and call super.paintComponent())
 * in order to respect the paint chain.
 * 
 */
@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    if (getParent() != null) { //Paint according to parent
        Graphics g2 = (Graphics2D) g;
        //Calculations
        int posX = Math.round(getParent().getWidth() / 100) * 20;
        int posY = Math.round(getParent().getHeight() / 100) * 20;
        int Width = Math.round(getParent().getWidth() / 100) * 80;
        int Height = Math.round(getParent().getHeight() / 100) * 80;
        g2.drawOval(posX, posY, Width, Height);
    }
}

您做的另一件事是没有必要的：

@Override
public int getWidth() {
    return this.Width;
}

覆盖组件的getWidth和getSize不会带您到任何地方。

[我建议您阅读的另一个有用链接是the Initial Threads和Why shouldn't I call setVisible(true) before adding components?

完整示例：

public class ClockViewer {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(()->{
            // create frame
            JFrame frame = new JFrame();
            final int Frame_Width = 110;
            final int Frame_Height = 130;

            // set frame attributes
            frame.setSize(Frame_Width, Frame_Height);
            frame.setTitle("A Really Descriptive Title...");

            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

            // get pane attributes
            System.out.println(frame.getContentPane().getWidth());
            System.out.println(frame.getContentPane().getHeight());

            // create ellipse
            JComponent ellipse = new JComponent() {
                @Override
                protected void paintComponent(Graphics g) {
                    super.paintComponent(g);
                    if (getParent() != null) { //Paint according to parent
                        Graphics g2 = (Graphics2D) g;
                        //Calculations
                        int posX = Math.round(getParent().getWidth() / 100) * 20;
                        int posY = Math.round(getParent().getHeight() / 100) * 20;
                        int Width = Math.round(getParent().getWidth() / 100) * 80;
                        int Height = Math.round(getParent().getHeight() / 100) * 80;
                        g2.drawOval(posX, posY, Width, Height);
                    }
                }
            };
            frame.add(ellipse);
            frame.setVisible(true);
        });

    }
}