下面是生成一个依赖窗口的对话框，属性为modal，请把所缺的代码补齐。
import java.awt.*；
public class DialogDemo extends Frame

DialogDemo ( )

SetTitle ("Demo");
Panel p=new Panel();
p.add(new label ("one"));
p.add(new Checkbox("two"));
add ("North",p);
add ("Center", new TextArea ("three", 3,10));
Dialog d=new Dialog(this,"a cat", 【12】 );
d.add("North",new Label ("Modal dialog");
d.add("Center",new TextArea("hello");
d.pack ();
d.show();

public static void main(String args[] )

DialogDemo f=new DialogDemo();
f.pack();
f.show ();