When looking for a lap for productivity or any general-purpose nowadays you will need more than 8GB of RAM.
Having an SSD for boot drive and storage will make your laptop snappy and responsive.
Getting a current-gen CPU will help you not getting outdated soon, and more cores always help in a productivity use case.
It depends on the tools you will be using for your development task and the hours of work you will do on a daily basis.
If you are thinking of a workstation laptop, then this would be the best choice for development work. My friends have been using Lenovo T series workstation whole day at his office for the past couple of years.
He runs multiple tools like android studio, eclipse, etc.
You can also go with ultrabooks, notebooks. These are also doing a pretty good job, but I don't recommend it as these are not for heavy usage.
I worked a few times with Android Studio developing a project for some work at university. Had a lot of problems with the "old" laptops of the university. I recommend you minimum of 16 GB of RAM, a good processor and a good graphic card.