Java Interview @ Indie Games

Hi Friends,

In this post, I'm sharing java interview questions and answers asked in Indie games.

Question 1:

How do you kill a thread in java?

Answer:

There are two ways to kill a thread:

• Stop the thread [Deprecated now]
• Use a volatile variable and running thread will keep checking it's value and return from it's run method in an orderly fashion. 

Question 2:

Why is Thread.stop() deprecated?

Answer:

Because it is inherently unsafe. Stopping a thread causes it to unlock all the monitors that it has locked.(The monitors are unlocked as the ThreadDeath exception propagates up the stack.)

If any of the objects previously protected by these monitors were in an inconsistent state, other threads may now view these objects in an inconsistent state. Such objects are said to be damaged.

When threads operate on damaged objects, arbitrary behavior can result. This behavior may be subtle and difficult to detect.

ThreadDeath exception kills thread silently, thus the user has no warning that this program may be corrupted.

 

Question 3:

How to check if a String is numeric in java?

Answer:

We can use Apache Commons Lang 3.4 and 3.5 versions.

StringUtils.isNumeric() or NumberUtils.isParsable().

Question 4:

How can we timeout a thread? I want to run a thread for some fixed amount of time.If it is not completed within that time, I want to either kill it or throw some exception. How to do it?

Answer:

We can use ExecutorService framework of Java 5.

public class Test{

    public static void main(String[] args){

        ExecutorService service = Executors.newSingleThreadExecutor();

        Future<String> future = service.submit(new Task());

        try{

            future.get(4, Timeout.SECONDS);

        }

        catch(Exception e){

            future.cancel(true);

        }

        executor.shutDownNow();

    

    }

}

class Task implements Callable<String>{

    @Override

    public String call() throws Exception{

        Thread.sleep(5000);

        return "";

    }

}

In this code, thread sleeps for 5 seconds, but future will wait for 4 seconds and it will timeout and cancel it.

Question 5:

How to wait for all threads to finish using ExecutorService?

Answer:

We can use shutdown() and awaitTermination() methods of ExecutorService.

ExecutorService service = Executors.newFixedThreadPool(4);

while(...){

    service.execute(new Task());

}    

service.shutdown();

try{

    service.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);

}

catch(InterruptedException e){

}

Question 6:

Can we create deadlock without thread in java?

Answer:

It is not possible to run the code without atleast one thread. A single thread can block itself in some cases e.g. attempting to upgrade a read lock to a write lock.

When a thread resource starves, it is called a livelock.

It is also possible to create a deadlock without creating an additional thread e.g. the finalizer thread and the main thread can deadlock each other.

That's all for this interview post.

Thanks for reading!!