Why is run() not immediately called when start() called on a thread object in java

java multithreading runnable
pi. picture pi. · Apr 22, 2010 · Viewed 7.5k times · Source

Or is it?
I have a thread object from: 

Thread myThread = new Thread(pObject);

Where pObject is an object of a class implementing the Runnable interface and then I have the start method called on the thread object like so:

myThread.start();

Now, my understanding is that when start() is called, the JVM implicitly (and immediately) calls the run() method which may be overridden (as it is in my case)

However, in my case, it appears that the start() method is not called immediately (as desired) but until the other statements/methods are completed from the calling block i.e. if I had a method after the start() call like so:

myThread.start();
doSomethingElse();

doSomthingElse() gets executed before the run() method is run at all.
Perhaps I am wrong with the initial premise that run() is always called right after the start() is called. Please help! The desired again is making executing run() right after start(). Thanks.

Answer

Michael Borgwardt picture Michael Borgwardt · Apr 22, 2010

Um... the run() method will run in a different thread. That, per definition, means you cannot make any assumptions about before or after which statements in the current thread it will execute, unless you synchronize them explicitly.

Related questions

"implements Runnable" vs "extends Thread" in Java

From what time I've spent with threads in Java, I've found these two ways to write threads: With implements Runnable: public class MyRunnable implements Runnable { public void run() { //Code } } //Started with a "new Thread(new MyRunnable()).start()" call Or, with …

Read More
The difference between the Runnable and Callable interfaces in Java

What is the difference between using the Runnable and Callable interfaces when designing a concurrent thread in Java, why would you choose one over the other?

Read More
What's the difference between Thread start() and Runnable run()

Say we have these two Runnables: class R1 implements Runnable { public void run() { … } … } class R2 implements Runnable { public void run() { … } … } Then what's the difference between this: public static void main() { R1 r1 = new R1(); R2 r2 = new R2(); r1.run(); …

Read More