Concurrency QuizS2C Home « Concurrency Quiz

The questions in this Java quiz are on the topics covered in the Java - Concurrency section of the site. The table below lists the lessons, a description of the lesson content and the the quiz question number range.

Lesson Summary

Click on a lesson in the table to go to that lesson for a refresher on the topics for that lesson.

API Contents Lessons	Description	Question Range
Lesson 1 - Thread Basics	In our first lesson of this section we look at multithreading and how to run parts of a program concurrently by subclassing the `Thread` class.	1 - 6
Lesson 2 - The `Runnable` Interface	The second way of running parts of a program concurrently is by declaring a class that implements the `Runnable` interface and is the subject of this lesson.	7 - 12
Lesson 3 - Synchronization	In this lesson we look at synchronization and how we can control access to our code at the method or block level.	13 - 17
Lesson 4 - Thread Priorities	For this lesson we investigate thread priorities and how we can have the priority set automatically by the invoking thread or assign thread priorities ourselves using methods of the `Thread` class.	18 - 22
Lesson 5 - Thread Communication	In our final lesson of the section we explore how threads can communicate with each other when they are within a synchronized method or code block.	23 - 28

Java Quiz

The quiz below tests your knowledge of the material learnt in the Java - Concurrency section of the site.

Question 1 : When we start up the JVM what kind of thread is created?

A begin thread
A daemon thread
A start thread
A user thread

- When we start up the JVM a non-daemon thread also known as a user thread is created.

Next >>

Question 2 : thread based multitasking allows us to run different programs concurrently?

true
false

- thread based multitasking allows us to run different parts of the same program concurrently. Running different programs at the same time is known as process based multitasking.

<< Prev

Next >>

Question 3 : What should subclasses of the Thread class do with that classes run() method?

use it to run threads
call one of its overloaded methods
override it
ignore it

- Subclasses of the <code>Thread</code> class should override the <code>run()</code> method to do bespoke processing.

<< Prev

Next >>

Question 4 : When creating multiple threads in a program, they execute in the same order as they were started in, using the start() method of the Thread class?

true
false

- We have no control over the actual order that threads will execute in. The <code>start()</code> method just readies a thread for execution and makes no difference to when it runs.

<< Prev

Next >>

Question 5 : The interrupt() method of the Thread class will not stop a thread executing?

true
false

- The <code>interrupt()</code> method doesn't actually stop a thread from running, but sets a flag in the thread that indicates that an interrupt has been requested. The flag must be checked in the <code>run()</code> method for its effect to have any impact.

<< Prev

Next >>

Question 6 : The sleep() method of the Thread class will stop a thread executing?

false
true

- The <code>sleep()</code> method moves a thread to a blocked state for the amount of time specified in its parameters. The thread will then pass back into a runnable state and be available to the thread scheduler again.

<< Prev

Next >>

Question 7 : Which method of the Runnable interface do we use to turn Thread instances into threads of execution?

run()
start()
Either of the above
None of the above

- We use the <code>start()</code> method of the <code>Thread</code> class to turn a <code>Thread</code> instance into a thread of execution.

<< Prev

Next >>

Question 8 : What is an advantage of using the Runnable interface?

Threads run faster
Easier to code
We are free to extend another class
We can have multiple run() methods

- Using the <code>Runnable</code> interface rather than subclassing the <code>Thread</code> class, leaves us the option of extending another class.

<< Prev

Next >>

Question 9 : What should we do with the run() method of the Runnable interface?

use it to run threads
call one of its overloaded methods
override it
ignore it

- Classes that implement the <code>Runnable</code> interface should override the <code>run()</code> method to do bespoke processing.

<< Prev

Next >>

Question 10 : To delay a thread until another thread has died we use the sleep() method of the Thread class?

true
false

- The <code>sleep()</code> method stops a thread executing for the duration specified, which may or may not be till another thread dies. To delay a thread until another thread has died we use the <code>join()</code> method.

<< Prev

Next >>

Question 11 : How can we find out which thread is active in the run() method at any given time?

Using the this keyword
We cannot find out this information
Using the getName() method
Using the static currentThread() method

- We can use the static <code>currentThread()</code> method to get a reference to the currently executing thread, which can then be used to get information such as the thread name.

<< Prev

Next >>

Question 12 : How does a thread know which run() method to call?

By the class
By the arguments passed to the run() method
By the constructor
By the start() method

- If the thread was constructed using a separate <code>Runnable</code> object, then that <code>Runnable</code> object's <code>run()</code> method is called; otherwise, the <code>run()</code> method from the <code>Thread</code> class is executed which does does nothing and returns, unless overridden by a sublass of the <code>Thread</code> class.

<< Prev

Next >>

Question 13 : Only one thread can enter a synchronized method at a time?

true
false

- Many threads can enter the same synchronized method concurrently if the threads are associated with different objects.

<< Prev

Next >>

Question 14 : Threads for the same object can enter different synchronized methods of a class concurrently?

true
false

- When a thread enters a synchronized non-static method the object gets locked. This means that all synchronized non-static methods are now locked out for this object until the method ends and releases the lock or other synchronized methods are called from this synchronized method as this thread already has the lock.

<< Prev

Next >>

Question 15 : We can run a synchronized static method and a synchronized non-static method at the same time?

true
false

- Yes this is possible. Synchronized static methods have a class lock and synchronized non-static methods have an object lock that are totally independent and therefore these methods can run concurrently.

<< Prev

Next >>

Question 16 : We must make local variables thread safe through synchronization?

true
false

- Every thread gets its own set of local variables which work independently of each other, so are inherently thread safe.

<< Prev

Next >>

Question 17 : When a lock is released from an object it dies and this is known as a deadlock?

true
false

- A deadlock occurs when the object locks of two or more objects are locking each other out forever.

<< Prev

Next >>

Question 18 :Setting a threads priority to 0 effectively stops the thread from running?

true
false

- Whatever valid priority (range 1-10) you set a thread to, has no effect on blocking the thread.

<< Prev

Next >>

Question 19 : We can set a thread's priority to a number within which range?

0-10
0-100
1-10
1-100

- A thread can be set in the range <code>1-10</code>.

<< Prev

Next >>

Question 20 : A new thread will have the default priority of 5 if not given a priority?

true
false

- New threads are given the threads priority of their parent thread which can be any value in the range <code>1-10</code>.

<< Prev

Next >>

Question 21 : We can use the yield() method to block a thread to give other threads a chance to run?

true
false

- The <code>yield()</code> method sets a thread back to a runnable state not a blocked state.

<< Prev

Next >>

Question 22 : A yielded thread may go straight back to executing after yielding?

true
false

- A yielded thread goes back to a runnable state and so can indeed be the next thread picked by the scheduler to execute.

<< Prev

Next >>

Question 23 : Which of the following methods releases an object's lock?

join()
notify()
sleep()
wait()
yield()

- The <code>wait()</code> method releases an object's lock.

<< Prev

Next >>

Question 24 : The notify() method returns all waiting threads for an object back to a runnable state?

true
false

- The <code>notify()</code> method will alert and return a single thread for an object back to a runnable state. The <code>notifyAll()</code> method will alert and return all threads for an object back to a runnable state.

<< Prev

Next >>

Question 25 : We can only use notify(), notifyAll() and wait() in synchronized methods?

true
false

- We can use the <code>notify()</code>, <code>notifyAll()</code> and <code>wait()</code> methods in synchronized methods and synchronized blocks of code.

<< Prev

Next >>

Question 26 : When using the wait() and notify() methods the object type makes no difference?

true
false

- The <code>Thread</code> class uses <code>wait()</code> and <code>notifyAll()</code> on threads to internally implement <code>join()</code>. So an instance of this class will do a <code>notifyAll()</code> when it dies unlike other object types.

<< Prev

Next >>

Question 27 : The notify() and notifyAll() methods will only awaken threads that are currently waiting on an object's lock?

true
false

- This is true as any threads that enter a wait state after the call to <code>notify()</code> or <code>notifyAll()</code> will be in a wait state until another call to <code>notify()</code> or <code>notifyAll()</code> has been made or indefinitely.

<< Prev

Next >>

Question 28 : Why do we need to put calls to wait() inside a loop statement?