When you hover the mouse cursor over a fragment of your code while holding down the Ctrl key on the keyboard, that fragment of the code can turn into a hyperlink.

当您在代码片断上移动鼠标时，同时按下键盘上的Ctrl键，这个代码片断就会变成超链接。

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Listing 15. Code fragment of the key-up event handler for handling the up Arrow and Down Arrow keys.

清单15 . key - up事件处理程序中处理up Arrow和Down arrow键的代码片段。

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