Key Insights
Thread.run() is just another method call
It executes synchronously on the calling thread—no JVM wizardry, no parallelism.
Thread.start() actually starts a thread
It schedules run() on a new JVM-managed worker, unlocking real multi-core action.
## Common Misunderstandings
### “Calling run() starts my thread”
Reality hits: it doesn’t. You’re craving scheduling magic from a plain method. Calling run() is like hiring a sous-chef and having them wash your own dishes.
### “I extended Thread, so I’m concurrent”
Subclassing gives you a run() implementation, but without start(), it never leaves the lot—think of it as a robot stuck at the charging dock.
## Trends in Modern Java Concurrency
### Favor Runnable for Composition
Most teams prefer new Thread(runnable).start() over extends Thread. It’s like using interchangeable kitchen tools instead of a single-purpose gadget.
### Virtual Threads (Project Loom)
Even with lightweight threads, you still call start-like APIs. Invoking run() remains ordering your robot to stand still.
## Real-World Pitfalls
### The DB Cleanup Bottleneck
Offloading cleanup with cleanupThread.run(); doesn’t free the main process—it blocks it. Thirty seconds of “parallel” waiting yields zero throughput.
### Synchronous Unit Tests
Calling run() can be handy for deterministic tests, but letting that habit bleed into production is like using table salt for a gourmet recipe—technically valid, but why?
Could your threads BE any more single-minded?
Use start() for real concurrency—unless you’re a fan of single-threaded thrill rides.
