SCJP Java Threads and Concurrency

Question 1

Which of the following is a correct way to create a new thread in Java?

Accepted Answer

Extend Thread class or implement Runnable interface

Answer

Implement Callable interface only

Answer

Extend Runnable class

Answer

Use the Process class

Question 2

What does the `synchronized` keyword ensure in Java?

Accepted Answer

That only one thread executes the synchronized block/method at a time

Answer

That a method runs faster

Answer

That threads run in a fixed sequence

Answer

That variables are stored in CPU cache

Question 3

What is a deadlock in Java threading?

Accepted Answer

Two or more threads permanently blocked waiting for each other's locks

Answer

A thread that runs indefinitely

Answer

A thread that throws an exception

Answer

A thread that uses too much memory

Question 4

What is the difference between `Thread.sleep()` and `Object.wait()` in Java?

Accepted Answer

wait() releases the object's lock; sleep() does not release any lock

Answer

sleep() releases the lock; wait() holds it

Answer

They are identical

Answer

sleep() is for threads; wait() is for processes

Question 5

Which thread state indicates that a thread is eligible to run but waiting for CPU time?

Accepted Answer

RUNNABLE

Answer

BLOCKED

Answer

WAITING

Answer

NEW

Question 6

What method must be overridden when implementing the `Runnable` interface?

Accepted Answer

run()

Answer

start()

Answer

execute()

Answer

launch()