Re: A question about Java Thread

Knute Johnson <>
Thu, 14 Jun 2007 10:49:08 -0700
Lew wrote:

JTL.zheng wrote:

I see a code like this:

in a Thread:
public void run() {

  Thread currentThread = Thread.currentThread();

  while (thread == currentThread) {

    try {
    catch (InterruptedException ex) {


what's the "while (thread == currentThread) " codes mean?
what is it used for?

There really needs to be more context to be certain. I will make a
guess, though. Apparently 'thread' is an instance variable or final
method variable from outside the Runnable that keeps track of some sort
of "active" Thread knowledge.

If you provide a short, complete example we'll know better.

One observation - the code you're reading might be flawed. It uses the


But sleep() is a static method, so it should not be called via the
instance 'thread' but via the class 'Thread':


The instance reference implies to some people that sleep() operates on
the specified instance; it does not, necessarily. (In this example it
works because the logic 'thread == currentThread' guarantees that
'thread' refers to the current Thread, so the two idioms are equivalent
this time, luckily.)

To make the logic clear, static methods should be called via class
references, not object references.

This used to be a fairly commonly seen bit of code for applets. The
thread reference is changed somewhere else (eg. the stop method) to end
the execution of this run method. You don't see many people writing
applets or asking questions about them here very often.


Knute Johnson
email s/nospam/knute/

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