In simple projects it's fundamentally what you describe. But there are some fancy libraries which e.g. require bytecode weaving (some AOP libraries, JPA impleme

In simple projects it's fundamentally what you describe. But there are some fancy libraries which e.g. require bytecode weaving (some AOP libraries, JPA implementations) or generate code from annotations. The other thing is that maven and gradle aren't just pure build tools, but they serve other roles too - chiefly dependency management, they are test runners, generate reports from those tests, can upload the generated JARs into artifact repositories, run the built application etc.