Android application (APK) files contain executable bytecode files in
the form of Dalvik Executable (DEX) files, which contain the compiled
code used to run your app. The Dalvik Executable specification limits
the total number of methods that can be referenced within a single DEX
file to 65,536, including Android framework methods, library methods,
and methods in your own code. Getting past this limit requires that
you configure your app build process to generate more than one DEX
file, known as a multidex configuration.
You should read official guide line about Building Apps with Over 64K Methods