Java Threads Quiz

What is the main purpose of the run() method in a thread?

• To terminate the thread

• To pause the thread

• To execute the code in a separate thread

• To create a new thread

Answer explanation

The run() method is crucial for executing the code in a separate thread. It defines the task that the thread will perform when started, allowing concurrent execution of code.

Which class must be extended to create a thread in Java?

• java.util.concurrent

• java.lang.Object

• java.lang.Thread

• java.lang.Runnable

Answer explanation

To create a thread in Java, you must extend the java.lang.Thread class. This allows you to override the run() method, which contains the code that will be executed when the thread is started.

What state is a thread in after it has been created but not started?

• New

• Dead

• Running

• Runnable

Answer explanation

A thread is in the 'New' state after it has been created but not yet started. It transitions to 'Runnable' when it is ready to run, but until then, it remains in the 'New' state.

What happens when a thread's run() method completes?

• The thread can be restarted

• The thread is considered dead

• The thread goes to the runnable state

• The thread is paused

Answer explanation

When a thread's run() method completes, it cannot be restarted and is considered dead. This means it has finished its execution and cannot be reused, which is why the correct answer is that the thread is considered dead.

Which method is used to start a thread?

• begin()

• start()

• run()

• execute()

Answer explanation

The correct method to start a thread in programming is 'start()'. This method initializes the thread and invokes the 'run()' method in a new thread of execution, allowing concurrent operations.

What is the role of the thread scheduler?

• To create new threads

• To manage thread states

• To decide which thread runs at any moment

• To terminate threads

Answer explanation

The thread scheduler's primary role is to decide which thread runs at any moment, ensuring efficient CPU utilization and responsiveness. While it can manage thread states and create or terminate threads, its main function is scheduling.

Which of the following is NOT a state of a thread?

• Running

• New

• Active

• Runnable

Answer explanation

The correct answer is 'Active' because it is not a recognized state of a thread. The valid states include 'Running', 'New', and 'Runnable', which describe the lifecycle of a thread in programming.

What does the synchronized keyword do?

• It creates a new thread

• It allows multiple threads to run simultaneously

• It controls the order of thread execution

• It terminates a thread

Answer explanation

The synchronized keyword in Java ensures that only one thread can access a block of code or method at a time, thus controlling the order of thread execution and preventing thread interference.

Which method must be called to wait for a thread to finish?

• notify()

• sleep()

• wait()

• join()

Answer explanation

The correct method to wait for a thread to finish is 'join()'. This method blocks the calling thread until the thread whose join() method is called has completed its execution, ensuring proper synchronization.

What is a potential problem when multiple threads access shared data?

• Thread creation

• Race conditions

• Thread termination

• Thread scheduling

Answer explanation

Race conditions occur when multiple threads access shared data simultaneously, leading to unpredictable results. This is a significant problem in concurrent programming, making 'race conditions' the correct answer.