Troubleshoot slow compilation

Question

What should I do to investigate and troubleshoot a slow compilation problem?

My project has about 100 classes and takes more than 45 seconds to compi

Answer 1

One not so well known feature of Java 8 is Generalized Target-Type Inference.

While it allows to write clearer code, this requires more work for Javac. Sometimes this results in exponential complexity of the type inference problem. This is a known issue, but unfortunately still unresolved - see JDK-8055984, JDK-8067767.

The workaround is to compile at Java 7-compatibility level: javac -source 7, or just to use simpler constructions.