Technically speaking, Android doesn't fully support Java 6. It's only a partial implementation of Java, since Java is overweight. The Android team has been adding requested features to the SDK in piecemeal form.
With that said, you can already get Java 8 lambdas in Android using the retrolambda project.
How does this work with a jar which contains classes using java8 features? Will it work in this situation or is it only for classes to be compiled? Can retrolambda be applied in other situations to keep the java version at 6 but use java 8 features?
With that said, you can already get Java 8 lambdas in Android using the retrolambda project.
http://zserge.com/blog/android-lambda.html