它是一个顶级窗口，具有边框、标题和可选菜单栏。

It is a top-level window with a border, title, and optional menu bar. Listing 3 shows the declaration of the calculator's frame.

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JFace窗口实际上不是顶级窗口的GUI对象(SWT已经提供了一个，名为Shell)。

A JFace window is not actually the GUI object for a top-level window (SWT already provides one, called a shell).

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例如，在顶级窗口完全移动到屏幕之外或者某个子对象移动到容器视区边界外部的时候。

For example, when a top-level window is moved completely off-screen or a child object is moved outside the boundaries of the container's viewport.

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