java - 为什么在这个例子中我们不能使用图形对象绘制字符串

Question

我想使用 init 方法绘制一个字符串，但如果使用内部 start 方法，那么它的工作正常。请解释一下

    public class Canv extends Applet //applet class 
    {   
        public void start()
        {

        }
         public void init()
        {                                     
            System.out.println("hi");
            Canvas c=new Canvas();              // want to print String in canvas

            c.setSize(500,500);
            c.setBackground(Color.red);
            add(c);
            Graphics g=c.getGraphics();  
            g.drawString("hello buddy",60,60); 
        }
        public void paint(Graphics g)
        {

        }
        public void stop()
        {
            System.out.println("stop");
        }
    }

Answer 1

如果你仔细阅读Java提供的API，那么你会看到init:

 * Called by the browser or applet viewer to inform
 * this applet that it has been loaded into the system. It is always
 * called before the first time that the <code>start</code> method is
 * called.
 * <p>
 * A subclass of <code>Applet</code> should override this method if
 * it has initialization to perform. For example, an applet with
 * threads would use the <code>init</code> method to create the
 * threads and the <code>destroy</code> method to kill them.

对于开始:

 * Called by the browser or applet viewer to inform
 * this applet that it should start its execution. It is called after
 * the <code>init</code> method and each time the applet is revisited
 * in a Web page.

显然，使用此接口(interface)操作 Java 小程序的代码不会显示 init() 方法中编写的 Canvas ，因为此时的 UI 尚未准备好。这只是容器开始初始化您的应用程序的一个标记。