(in Android) Do Activity classes need to be in a separate .java file?

I am new to android development and am currently working my way through the "Hello..." Tutorials on the developer website.

I got stuck on the Tab Layout walkthrough and the only way I could r开发者_如何转开发esolve it was to put each Activity Class in a separate .java file.

I was wondering if all Activities need to be in separate .java files, or am I missing something.

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See this question. The answer is no, because Java does not allow it (with the exceptions discussed in the responses to my link).