if Thread.sleep is static, how does individual thread knows it is put to sleep?

Question

I am a bit confused with Thread.sleep() method. if Thread.sleep() is a static method, how does two threads know which is put to sleep. For example,

Answer 1

Does it mean Thread.sleep() puts the current Thread to sleep?

Yes. Only the current thread can do that.

What if t1 wants to put t to sleep. that shouldn't be possible correct?

Right. You can set a volatile boolean flag that will cause another thread to call Thread.sleep(...) but another thread can't cause a thread to sleep.

 volatile boolean shouldSleep = false;
 ...
 // check this flag that might be set by another thread to see if I should sleep
 if (shouldSleep) {
     Thread.sleep(...);
 }

Answer 2

It can find the current thread from Thread.currentThread(). The current thread only can put itself to sleep.