What do we understand by a deadlock?

A deadlock is a situation in which two (or more) threads are each waiting on the other thread to free a resource that it has locked, while the thread itself has locked a resource the other thread is waiting on:
Thread 1: locks resource A, waits for resource B
Thread 2: locks resource B, waits for resource A

What do we understand by an atomic operation?

An atomic operation is an operation that is either executed completely or not at all.

After having started a child thread, how do we wait in the parent thread for the termination of the child thread?

Waiting for a thread’s termination is done by invoking the method join() on the thread’s instance variable: --

How should an InterruptedException be handled?

Methods like sleep() and join() throw an InterruptedException to tell the caller that another thread has interrupted this thread. In most cases this is done in order to tell the current thread to stop its current computations and to finish them unexpectedly. Hence ignoring the exception by catching it and only logging it to the console or some log file is often not the appropriate way to handle this kind of exception. The problem with this exception is, that the method run() of the Runnable interface does not allow that run() throws any exceptions. So just rethrowing it does not help. This means the implementation of run() has to handle this checked exception itself and this often leads to the fact that it its caught and ignored.

What is a daemon thread?

A daemon thread is a thread whose execution state is not evaluated when the JVM decides if it should stop or not. The JVM stops when all user threads (in contrast to the daemon threads) are terminated. Hence daemon threads can be used to implement for example monitoring functionality as the thread is stopped by the JVM as soon as all user threads have stopped:
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The example application above terminates even though the daemon thread is still running in its endless while loop.

What is the output of the following code?

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The code above produces the output “main” and not “myThread”. As can be seen in line two of the main() method, we invoke by mistake the method run() instead of start(). Hence, no new thread is started, but the method run() gets executed within the main thread.

How do we stop a thread in Java?

To stop a thread one can use a volatile reference pointing to the current thread that can be set to null by other threads to indicate the current thread should stop its execution:

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