Why Activity page jump stops running

Eclipse which was built between several interface which has a jump jump mistakes, not being given the program runs, the rest of the interface to jump properly, it would be wrong to stop running jump to the interface, which experts under the guidance of rookie! ! ! Also ask, Does anyone know how to map data MapGis google map affixed to call together? ? Thank
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I guess what's null pointer
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The problem lies here:
Caused by: java.lang.NullPointerException
at com.example.wu.activity.onCreate (activity.java: 20)
You look com.example.wu.activity.onCreate in the first 20 lines of code what is wrong?
Is not an object associated with the line 20 does not initialize
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Did not seem to display an error code, ah, that activity interface code below, I also hope an expert to look ah,

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J1 seemingly empty, and look at the configuration file, j1 configuration is not anything wrong id or
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The monitor should be okay and j1, j1, j2, j3 three listeners into this interface will be some jump button, and now the key is to listen from another interface than the interface button to jump ah! ! !
Starting with the jump, and later because the button more, in order to facilitate the management, I have changed the name of the button down, then there is this problem,,
I then R.java posted, then trouble you to look at, to participate in the development of competition, what they do not learn by doing! !

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I have encountered this problem, I do not know ah Editor's Note
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Great God answers you seek
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Ah, I know. I have an activity to jump in AndroidManifest not registered, so hop on to that activity, it stopped abnormally.