Question

I want a method that runs 2 or more methods in separate threads. I want be sure that method won’t finish before all threads are done.

Answer 1

The best approach is to utilize the Executor Service API to manage a thread pool instead of starting an open-ended number of threads on your own.

ExecutorService pool = Executors.newCachedThreadPool();
for (Runnable r : new Runnable[] {
    new R() { void r() { myMethod1(); }},
    new R() { void r() { myMethod2(); }},
})
  pool.execute(r);
pool.shutdown();
pool.awaitTermination(60, TimeUnit.SECONDS);

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abstract class R implements Runnable
  public final void run() { r(); }
  abstract void r();
}

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Note that it is not advisable to insist on every method running in its own, separate thread. Threads are quite heavyweight (each allocating a complete call stack) and performance actually decreases as the thread count increases far beyond the number of available processor cores.