import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class AppApplet  extends Applet {
           public static void main(String args[]) {
                    Frame frame=new Frame();
                    AppApplet app=new AppApplet();
                    app.init();
                    frame.add(app);
                    frame.setSize(400,100);
                    frame.show();
          }
          TextField tf=new TextField(10);
          Button b=new Button("求该数的平方“）；
          Lable b=new Lable("用于显示结果的标记”）；
          public void init() {
          setLayout(new FlowLayout() );
          add(tf);
          add(b);
          add(l);
          b.addActionListener(new BActionAdapter() );
         }
         class BActionAdapter implements ActionListener {
                  pubic void actionPerformed(ActionEvent e ) {
                            String s=tf.getText();
                            double d=Double.parseDouble(s);
                            double sq=d*d*d;
                            l.setText( d+"的立方是： “+sq);
        }
    }
}
顺便帮我看下有什么问题，反正照着书写的但编译不出来

AppApplet.java  
public 类的类名就是文件名.

我真时服了你了，你照着书都能出现这么多的错误。
下面时可以通过的代码：
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class AppApplet  extends Applet {
           public static void main(String args[]) {
                    Frame frame=new Frame();
                    AppApplet app=new AppApplet();
                    app.init();
                    frame.add(app);
                    frame.setSize(400,100);
                    frame.show();
          }
          TextField tf=new TextField(10);
          Button b=new Button("求该数的平方");
          Label l=new Label("用于显示结果的标记");
          public void init() {
          setLayout(new FlowLayout() );
          add(tf);
          add(b);
          add(l);
          b.addActionListener(new BActionAdapter() );
         }
         class BActionAdapter implements ActionListener {
                  public void actionPerformed(ActionEvent e ) {
                            String s=tf.getText();
                            double d=Double.parseDouble(s);
                            double sq=d*d*d;
                            l.setText( d+"的立方是： "+sq);
        }
    }
}

就是啊！！好好看看书 ！！

谢谢各位兄弟，已经解决！