How can I use external JARs in an Android project?

For Eclipse

A good way to add external JARs to your Android project or any Java project is:

1. Create a folder called libs in your project's root folder
2. Copy your JAR files to the libs folder

3. Now right click on the Jar file and then select Build Path > Add to BuildPath, which will create a folder called 'Referenced Libraries' within yourproject

   By doing this, you will notlose your libraries that are being referenced on yourhard drive whenever you transfer your project to another computer.

For Android Studio

1. If you are in Android View in project explorer, change it to Project view as below

2. Right click the desired module where you would like to add the external library, then select New > Directroy and name it as 'libs'
3. Now copy the blah_blah.jar into the 'libs' folder
4. Right click the blah_blah.jar, Then select 'Add as Library..'. This will automatically add and entry in build.gradle as compile files('libs/blah_blah.jar') and sync the gradle. And you are done

Please Note : If you are using 3rd party libraries then it is better to use transitive dependencies where Gradle script automatically downloads the JAR and the dependency JAR when gradle script run.

Ex : compile 'com.google.android.gms:play-services-ads:9.4.0'

Read more about Gradle Dependency Mangement

Yes, you can use it. Here is how:

1. Your Project -> right click -> Import -> File System -> yourjar.jar
2. Your Project -> right click -> Properties -> Java Build Path -> Libraries -> Add Jar -> yourjar.jar

This video might be useful in case you are having some issues.

I'm currently using SDK 20.0.3 and none of the previous solutions worked for me.

The reason that hessdroid works where hess failed is because the two jar files contain java that is compiled for different virtual machines. The byte code created by the Java compiler is not guaranteed to run on the Dalvik virtual machine. The byte code created by the Android compiler is not guaranteed to run on the Java virtual machine.

In my case I had access to the source code and was able to create an Android jar file for it using the method that I described here: https://stackoverflow.com/a/13144382/545064