开始：Applet未初始化

Question

import java.applet.Applet;
import java.awt.Dimension;
import java.awt.Graphics;

public class snakeApplet extends Applet {

    private snakeCanvas c;

    public void init() {
        c.setPreferredSize(new Dimension(640, 480));
        c = new snakeCanvas();
        c.setVisible(true);
        c.setFocusable(true);
        this.add(c);
        this.setVisible(true);
        this.setSize(new Dimension(640, 480));
    }

    public void paint(Graphics g) {
        this.setSize(new Dimension(640, 480));
    }
}

Answer 1

你忘了问一个问题，但这是一个问题

c = new snakeCanvas();
c.setPreferredSize(new Dimension(640, 480));

在可以在实例

上调用任何方法之前，需要初始化变量c