zipalign doesn't change the apk file

zipalign -v 4 input.apk output.apk

several times for my changing application and the corresponding md5 from both input and output has always been the same, so they're the very same file. Isn't this tool suppose to perform certain optimizations, 开发者_运维知识库hence modify the file ?

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Perhaps it was already executed by your build process (i.e. ANT).

Also, pls read here: http://developer.android.com/guide/developing/tools/zipalign.html for more details.