### JFrame不具备模态窗口的条件 ``` Window类的构造： Window(GraphicsConfiguration gc){} //Frame和JFrame采用了这个构造方法 //下面这三个构造方法才能拓展出模态窗口，因为它们指定了一个Frame或Window作为其所有者 Window(Frame owner){} Window(Window owner){} Window(Window owner, GraphicsConfiguration gc){} Dialog继承的是Window类，它的构造如下： public Dialog(Frame owner, String title, boolean modal, GraphicsConfiguration gc) { super(owner, gc); //重点在这里，所以它可以设置模态 this.title = title; this.modal = modal; setFocusTraversalPolicy(KeyboardFocusManager.getCurrentKeyboardFocusManager().getDefaultFocusTraversalPolicy()); } JFrame和它的父类Frame的构造： public Frame(String title, GraphicsConfiguration gc) { super(gc); //采用了Window的第一种构造 init(title, gc); } ```