下列WindowListener接口方法中当窗口被激活时调用的方法是( )。

A
解析：本题考查关于窗口监听器接口中基本方法的知识。选项A正确，window Activated(WindowEvent)方法在窗口激活时被调用到：选项B错误，windowClosed (WindowEvent)方法在窗口已经被关闭时调用：选项C错误，windowOpened(WindowEvem)方法在窗口已经打开时被调用到；选项D错误， windowDeactivated(WindowEvent)方法与窗口不再激活时被调用到。故本题答案是A。