java - 线程 "AWT-EventQueue-0"和奇数 TextArea 中出现异常

Question

我目前正在尝试制作一个绘图 Canvas JFrame，其中设备的IP地址显示在底部(以帮助另一个设备在稍后阶段连接到同一个JFrame)，但我目前正在接收标题错误，以及其他一些问题。

问题:- AWT 错误(我假设这是导致此问题的 IP 调用)- JTextArea 仅在我最小化并重新打开 JFrame 后显示为黑色条 - 如果我再次执行此操作，黑色条将消失，然后最终显示我想要的 IP

我认为第二个问题与“绘画”运行的时间有关。我一直在摆弄代码，在当前阶段感觉就像是一个巨大的结。任何帮助解决列出的问题并重新获得一些控制权的帮助将不胜感激!

这是我的类(class):

public class CanvasFrame extends JPanel {

    ArrayList<Point> location = new ArrayList<Point>(); 

    JTextArea consoleOutput = new JTextArea(1,20);

    public void addComponentToPane(Container pane) {
        consoleOutput.setEditable(false);
    }

    public CanvasFrame() {
        addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                location.clear();
                location.add(e.getPoint());
            }
        });

        addMouseMotionListener(new MouseMotionAdapter() {
            @Override
            public void mouseDragged(MouseEvent e) {
                location.add(e.getPoint());
                repaint();
            }
        });
        setPreferredSize(new Dimension(800, 500));
        setBackground(Color.WHITE);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

         Point p = location.get(0);
         for (int i = 1; i < location.size(); i++) {
             Point q = location.get(i);
             g.drawLine(p.x, p.y, q.x, q.y);
             p = q;
         }
    }

    public static void main(String[] args) throws Exception {

        InetAddress SERVERIP = InetAddress.getLocalHost();

        Runnable runnable = new Runnable() {
            @Override
            public void run() {

                JFrame frame = new JFrame("Drawing with friends");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new CanvasFrame(), BorderLayout.CENTER);

                JTextArea IPadress = new JTextArea(1,20);
                IPadress.setEditable(false);
                IPadress.append("DEVICE IP: " + SERVERIP.getHostAddress());
                frame.add(IPadress, BorderLayout.SOUTH);

                frame.setSize(new Dimension(800,600));
                frame.setLocationRelativeTo(null);
                frame.setResizable(false);
                frame.setVisible(true);
            }
        };
        SwingUtilities.invokeLater(runnable);
    }
}

完全错误:

Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.rangeCheck(Unknown Source)
    at java.util.ArrayList.get(Unknown Source)
    at drawingwf.CanvasFrame.paintComponent(CanvasFrame.java:56)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JLayeredPane.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paintToOffscreen(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
    at javax.swing.RepaintManager.paint(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
    at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
    at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
    at java.awt.Container.paint(Unknown Source)
    at java.awt.Window.paint(Unknown Source)
    at javax.swing.RepaintManager$4.run(Unknown Source)
    at javax.swing.RepaintManager$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.access$1200(Unknown Source)
    at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.rangeCheck(Unknown Source)
    at java.util.ArrayList.get(Unknown Source)
    at drawingwf.CanvasFrame.paintComponent(CanvasFrame.java:56)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JLayeredPane.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paintToOffscreen(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
    at javax.swing.RepaintManager.paint(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
    at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
    at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
    at java.awt.Container.paint(Unknown Source)
    at java.awt.Window.paint(Unknown Source)
    at javax.swing.RepaintManager$4.run(Unknown Source)
    at javax.swing.RepaintManager$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.access$1200(Unknown Source)
    at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$500(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

在调用 mousePressed 或 mouseDragged 之前，paintComponent 中的 location 变量为空。

在访问0索引之前检查location是否为空:

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);

    // I add this
    if(location.isEmpty())
        return;

    Point p = location.get(0);
    for (int i = 1; i < location.size(); i++) {
        Point q = location.get(i);
        g.drawLine(p.x, p.y, q.x, q.y);
        p = q;
    }
}