I use a 3 year-old laptop with 32GB of RAM, an SSD, and a dual-core i7 (U-series) processor. It's reasonably efficient. I think the amount of RAM and the IO speed of my SSD remove most of the hardware bottlenecks I face.
However, I would like compile times to be faster, I do sometimes notice applications hanging, and IntelliJ (we use Java at work) seems limited on how many projects I can run efficiently in a single workspace. I'm just wondering whether a workstation-grade laptop (Dell Precision or Thinkpad P-series) would be a sufficient upgrade, or investing in a desktop would be worthwhile at some point.
Yes, either 17" machine offers an 8-core CPU and plenty of thermal capacity (i.e. larger chassis than their 15" equivalents), along with more than enough memory (128GB), and in Dell's case, a boatload of HD slots (4, run in whatever RAID config you want). These are desktop replacements, heavy (as in 6.5+ lbs), with 240W power bricks , so you'll probably want them to stay on the desk for most of the time.
I'm personally looking to replace my old Dell Precision with a 15" 5540, maxed out. For Scala work the extra cores help reduce build times, probably the same for Java.