线程主中的 java.lang.StackOverflowError

Question

我正在尝试在 Canvas 中绘制字符串。当我实例化扩展Canvas 的类时发生错误，为什么会得到它？

错误堆栈

at sun.awt.Win32GraphicsConfig.getBounds(Native Method)
at sun.awt.Win32GraphicsConfig.getBounds(Win32GraphicsConfig.java:222)
at java.awt.Window.init(Window.java:505)
at java.awt.Window.<init>(Window.java:537)
at java.awt.Frame.<init>(Frame.java:420)
at javax.swing.JFrame.<init>(JFrame.java:233)
at canvas.Canvas.<init>(Canvas.java:20)
at canvas.Canvas$DrawCanvas.<init>(Canvas.java:35)
at canvas.Canvas$DrawCanvas.<init>(Canvas.java:35)
at canvas.Canvas.<init>(Canvas.java:17)
at canvas.Canvas$DrawCanvas.<init>(Canvas.java:35)
at canvas.Canvas$DrawCanvas.<init>(Canvas.java:35)
at canvas.Canvas.<init>(Canvas.java:17)
at canvas.Canvas$DrawCanvas.<init>(Canvas.java:35)
at canvas.Canvas$DrawCanvas.<init>(Canvas.java:35)
at canvas.Canvas.<init>(Canvas.java:17)`

这是我的代码：

public class Canvas extends JFrame{

DrawCanvas cc = new DrawCanvas();

public Canvas(){
    super("Canvas");
    setVisible(true);
    setSize(100, 100);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    add(cc);
}

public static void main(String[] args) {
    Canvas c = new Canvas();
}

private class DrawCanvas extends Canvas{
    @Override
    public void paint(Graphics g){
        g.drawString("String", 10, 10);
    }
}
}

Answer 1

这就是你做错的地方：Canvas 构造函数创建了一个新的DrawCanvas，但DrawCanvas 扩展了Canvas，并且由于你没有指定不同的构造函数，它采用其超类的构造函数（Canvas），因此也产生了一个新的DrawCanvas，这又产生了另一个DrawCanvas...无限。因此你的代码：

new DrawCanvas()

导致无限递归。

您的意思是扩展java.awt.Canvas 吗？

此外，您可能希望避免为您的类赋予与 Java API 中相似的名称，尤其是，如果您使用的是那些名称相似的类。