1) You have thread T1, T2 and T3, how will you ensure that thread T2 run after T1 and thread T3 run after T2?
This thread interview questions is mostly asked in first round or phone screening round of interview and purpose of this multi-threading question is to check whether candidate is familiar with concept of "join" method or not. Answer of this multi-threading questions is simple it can be achieved by using join method of Thread class.
2) What is the advantage of new Lock interface over synchronized block in Java? You need to implement a high performance cache which allows multiple reader but single writer to keep the integrity how will you implement it?
The major advantage of lock interfaces on multi-threaded and concurrent programming is they provide two separate lock for reading and writing which enables you to write high performance data structure like ConcurrentHashMap and conditional blocking. This java threads interview question is getting increasingly popular and more and more follow-up questions come based upon answer of interviewee. I would strongly suggest reading Locks before appearing for any java multi-threading interview because now days Its heavily used to build cache for electronic trading system on client and exchange connectivity space.
3) What are differences between wait and sleep method in java?
Another frequently asked thread interview question in Java mostly appear in phone interview. Only major difference is wait release the lock or monitor while sleep doesn't release any lock or monitor while waiting. Wait is used for inter-thread communication while sleep is used to introduce pause on execution. See my post wait vs sleep in Java for more differences
4) Write code to implement blocking queue in Java?
This is relatively tough java multi-threading interview question which servers many purpose, it checks whether candidate can actually write Java code using thread or not, it sees how good candidate is on understanding concurrent scenarios and you can ask lot of follow-up question based upon his code. If he uses wait() and notify() method to implement blocking queue, Once interviewee successfully writes it you can ask him to write it again using new java 5 concurrent classes etc.
5) Write code to solve the Produce consumer problem in Java?
Similar to above questions on thread but more classic in nature, some time interviewer ask follow up questions How do you solve producer consumer problem in Java, well it can be solved in multiple way, I have shared one way to solve producer consumer problem using BlockingQueue in Java , so be prepare for surprises. Some time they even ask to implement solution of dining philosopher problem as well.
6) Write a program which will result in deadlock? How will you fix deadlock in Java?
Java thread interview questions and answers This is my favorite java thread interview question because even though deadlock is quite common while writing multi-threaded concurrent program many candidates not able to write deadlock free code and they simply struggle. Just ask them you have n resources and n thread and to complete an operation you require all resources. Here n can be replace with 2 for simplest case and higher number to make question more intimidating. see How to avoid deadlock in java for more information on deadlock in Java.
7) What is atomic operation? What are atomic operations in Java?
Simple java thread interview questions, another follow-up is do you need to synchronized an atomic operation? :) You can read more about java synchronization here.
8) What is volatile keyword in Java? How to use it? How is it different from synchronized method in Java?
Thread questions based on volatile keyword in Java has become more popular after changes made on it on Java 5 and Java memory model. It’s good to prepare well about how volatile variables ensures visibility, ordering and consistency in concurrent environment.
9) What is race condition? How will you find and solve race condition?
Another multi-threading question in Java which appear mostly on senior level interviews. Most interviewer grill on recent race condition you have faced and how did you solve it and some time they will write sample code and ask you detect race condition. See my post on Race condition in Java for more information. In my opinion this is one of the best java thread interview question and can really test the candidate's experience on solving race condition or writing code which is free of data race or any other race condition. Best book to get mastery of this topic is "Concurrency practices in Java'".
10) How will you take thread dump in Java? How will you analyze Thread dump?
In UNIX you can use kill -3 and then thread dump will print on log on windows you can use "CTRL+Break". Rather simple and focus thread interview question but can get tricky if he ask how you analyze it. Thread dump can be useful to analyze deadlock situations as well.
This thread interview questions is mostly asked in first round or phone screening round of interview and purpose of this multi-threading question is to check whether candidate is familiar with concept of "join" method or not. Answer of this multi-threading questions is simple it can be achieved by using join method of Thread class.
2) What is the advantage of new Lock interface over synchronized block in Java? You need to implement a high performance cache which allows multiple reader but single writer to keep the integrity how will you implement it?
The major advantage of lock interfaces on multi-threaded and concurrent programming is they provide two separate lock for reading and writing which enables you to write high performance data structure like ConcurrentHashMap and conditional blocking. This java threads interview question is getting increasingly popular and more and more follow-up questions come based upon answer of interviewee. I would strongly suggest reading Locks before appearing for any java multi-threading interview because now days Its heavily used to build cache for electronic trading system on client and exchange connectivity space.
3) What are differences between wait and sleep method in java?
Another frequently asked thread interview question in Java mostly appear in phone interview. Only major difference is wait release the lock or monitor while sleep doesn't release any lock or monitor while waiting. Wait is used for inter-thread communication while sleep is used to introduce pause on execution. See my post wait vs sleep in Java for more differences
4) Write code to implement blocking queue in Java?
This is relatively tough java multi-threading interview question which servers many purpose, it checks whether candidate can actually write Java code using thread or not, it sees how good candidate is on understanding concurrent scenarios and you can ask lot of follow-up question based upon his code. If he uses wait() and notify() method to implement blocking queue, Once interviewee successfully writes it you can ask him to write it again using new java 5 concurrent classes etc.
5) Write code to solve the Produce consumer problem in Java?
Similar to above questions on thread but more classic in nature, some time interviewer ask follow up questions How do you solve producer consumer problem in Java, well it can be solved in multiple way, I have shared one way to solve producer consumer problem using BlockingQueue in Java , so be prepare for surprises. Some time they even ask to implement solution of dining philosopher problem as well.
6) Write a program which will result in deadlock? How will you fix deadlock in Java?
Java thread interview questions and answers This is my favorite java thread interview question because even though deadlock is quite common while writing multi-threaded concurrent program many candidates not able to write deadlock free code and they simply struggle. Just ask them you have n resources and n thread and to complete an operation you require all resources. Here n can be replace with 2 for simplest case and higher number to make question more intimidating. see How to avoid deadlock in java for more information on deadlock in Java.
7) What is atomic operation? What are atomic operations in Java?
Simple java thread interview questions, another follow-up is do you need to synchronized an atomic operation? :) You can read more about java synchronization here.
8) What is volatile keyword in Java? How to use it? How is it different from synchronized method in Java?
Thread questions based on volatile keyword in Java has become more popular after changes made on it on Java 5 and Java memory model. It’s good to prepare well about how volatile variables ensures visibility, ordering and consistency in concurrent environment.
9) What is race condition? How will you find and solve race condition?
Another multi-threading question in Java which appear mostly on senior level interviews. Most interviewer grill on recent race condition you have faced and how did you solve it and some time they will write sample code and ask you detect race condition. See my post on Race condition in Java for more information. In my opinion this is one of the best java thread interview question and can really test the candidate's experience on solving race condition or writing code which is free of data race or any other race condition. Best book to get mastery of this topic is "Concurrency practices in Java'".
10) How will you take thread dump in Java? How will you analyze Thread dump?
In UNIX you can use kill -3 and then thread dump will print on log on windows you can use "CTRL+Break". Rather simple and focus thread interview question but can get tricky if he ask how you analyze it. Thread dump can be useful to analyze deadlock situations as well.
Some More FAQs:
1) Difference between green thread and native thread in Java?
2) Difference between thread and process?
3) What is context switching in multi-threading?
4) Difference between deadlock and livelock, deadlock and starvation?
5) What thread-scheduling algorithm is used in Java?
6) What is thread-scheduler in Java?
7) How do you handle un-handled exception in thread?
8) What is thread-group, why its advised not to use thread-group in Java?
9) Why Executor framework is better than creating and managing thread by application ?
10) Difference between Executor and Executors in Java?
10) How to find which thread is taking maximum cpu in windows and Linux server?
2) Difference between thread and process?
3) What is context switching in multi-threading?
4) Difference between deadlock and livelock, deadlock and starvation?
5) What thread-scheduling algorithm is used in Java?
6) What is thread-scheduler in Java?
7) How do you handle un-handled exception in thread?
8) What is thread-group, why its advised not to use thread-group in Java?
9) Why Executor framework is better than creating and managing thread by application ?
10) Difference between Executor and Executors in Java?
10) How to find which thread is taking maximum cpu in windows and Linux server?
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