java - How can sub-classing affects all instance of original object? -

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i trying learn decorator pattern wiki states the decorator pattern alternative subclassing. subclassing adds behavior @ compile time, , change affects instances of original class; decorating can provide new behavior @ run-time individual objects.

i have doubt, if create 1 class original original=new original(); how come subclassing subclass extends original affect original reference of object of class original, should remain intact?


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