How to add a jar in External Libraries in android studio

STEPS

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1. First switch your folder structure from Android to Project.

2. Now search for the libs folder inside app - build folder.

3. Once you have pasted the .jar file inside libs folder. 
4. Right click on the jar file and at end click on Add as library. 
5. This will take care of adding compile files('libs/ojdbc14.jar') in build.gradle [You don't have to manually enter this in your build file].

For manually, go to build.gradle and compile attached library. (For example)

dependencies {
  .....
    compile files('libs/ojdbc14.jar')

}

click on sync project

Now you can start using the library in your project.