— Scott McNealy, Sun Microsystems Chairman, President and ceo

3
myThread.start();
Nothing happens until you call the Thread’s 
start() method. That’s when you go from 
having just a Thread instance to having a new 
thread of execution. When the new thread 
starts up, it takes the Runnable object’s 
run() method and puts it on the bottom of 
the new thread’s stack.
Run
nable obje
ct
Thread objec
t 
Thread objec
t 
Runn
able obj
ec
t 
run()
launching a 
thread

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networking 
and
threads
you are here
4
493
Every Thread needs a job to do.
A method to put on the new thread stack.
A Thread object needs a job. A job the thread will run when the 
thread is started. That job is actually the first method that goes on 
the new thread’s stack, and it must always be a method that looks 
like this:
 
public void run() {
// code that will be run by the new thread
 
}
How does the thread know which method to put at the bottom of 
the stack? Because Runnable defines a contract. Because Runnable 
is an interface. A thread’s job can be defined in any class that 
implements the Runnable interface. The thread cares only that you 
pass the Thread constructor an object of a class that implements 
Runnable.
When you pass a Runnable to a Thread constructor, you’re really 
just giving the Thread a way to get to a run() method. You’re giving 
the Thread its job to do.
Runnable is to a 
Thread what a job is to 
a worker. A Runnable 
is the job a thread is 
supposed to run.
A Runnable holds the 
method that goes on