Interview questions on multithreading in java for experienced

 Part 3

Interview questions on multithreading in java for experienced covered in this post:

    What is Synchronization?

-          Synchronization is a technique used in a multi-threading environment to control the access of shared resources on multiple threads.

 

    What is the difference between Synchronization Method and Synchronized Block?

	Synchronization Method	Synchronized Block
1.	A method declared with a Synchronized keyword is called Synchronized Method.	Inside a method, if a chunk of code declared inside block with Synchronized keyword is called a Synchronized block.
2.	Performance is low as compared to Block.	Performance is high as compared to the method.

    What is the volatile keyword in java?

-          If you declare a variable as volatile, JVM will store those variables on main memory.

-          We can make sure every time JVM reads the value from the main memory.

-          Every time JVM writes the value it will write on the main memory.

-          Volatile keyword ensures that variable will be visible to all thread and thread can read the value from main memory.

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    What will happen If I directly override the run() method instead of the start() method?

-          First of all, when you invoke the start() method on a thread, New thread will create and start executing parallelly.

-          Run() method will execute as it is in the same thread.

-          Run() method will be treated as a normal overridden method of the Thread class.

 

    What will happen when an exception occurred in a thread?

-          Exception behaviour won’t change in the case of non-threading or multi-threading programming.

-          Once an exception occurs and if it is not handled then your program will be terminated abruptly.

-          In the case of a multi-threading environment if an exception occurs then the thread will die.

-          If an uncaught exception handler is registered then it will get a callback.

-          Nested interface Thread.UncaughtExceptionHandler is defined for handlers invoked when a Thread abruptly terminates due to an uncaught exception.

When a thread is about to terminate due to an uncaught exception the Java Virtual Machine will query the thread for its UncaughtExceptionHandler using

Thread.getUncaughtExceptionHandler() and will invoke the handler's uncaughtException() method, passing the thread and the exception as arguments.

 

    What is readwritelock in java?

-          A ReadWriteLock maintains a pair of associated locks.

-          One for read-only operations and one for writing.

-          It allows various threads to read a specific resource but allows only one to write it at a time.

-          The read lock may be held simultaneously by multiple reader threads, so long as there are no writers. The write lock is exclusive.

-          All ReadWriteLock implementations must guarantee that the memory synchronization effects of write-lock operations (as specified in the Lock interface) also hold with respect to the associated readLock. That is, a thread successfully acquiring the read lock will see all updates made upon the previous release of the write lock.

-          public interface ReadWriteLock {}.

 

    What is Thread-Local class? What is the purpose to have this class?

-          We can easily create classes whose fields are thread-local by simply defining private fields in the Thread class.

-          We can create thread-safe classes that don’t share states between threads by making their fields thread-local.

-          Thread-Local is most commonly used to implement per-request global variables in app servers or servlet containers where each user or client request is handled by a separate thread.

-          For example, Spring, Spring Security and JSF each have the concept of a "Context" through which functionality of the framework is accessed. And in each case, that context is implemented both via dependency injection (the clean way) and as a Thread-Local in cases where DI can't or won't be used.

-          Please refer the below example.

package simplifiedjava.crackedInterview;  import java.util.Arrays; import java.util.List;  public class ThreadLocalDemo1 extends Thread {        private final List<Integer> numList = Arrays.asList(10,20,30,40,50);          @Override       public void run() {             for(int n : numList) {                   System.out.println(n);             }       } }  package simplifiedjava.crackedInterview;  import java.util.Arrays; import java.util.List;  public class ThreadLocalDemo2 extends Thread{        private final List<String> wordList = Arrays.asList("Hi","Hello","GM","GA","GN");            @Override       public void run() {             for(String str : wordList) {                   System.out.println(str);             }       } }

 

    What is the ThreadGroup?

-          Thread group represents a set of threads.

-          ThreadGroup belongs to java.lang.ThreadGroup.

-          A thread is allowed to access information about its own thread group but not to access information about its thread group's parent thread group or any other thread group.

-          A thread group can also include the other thread group. The thread group creates a tree in which every thread group except the initial thread group has a parent.

 

    What is a Thread pool?

-          Thread pool is a set of threads that resides in a single place.

    What is the difference between volatile and atomic variable?

-          Volatile Variable: Volatile keyword is used in java synchronization technique to achieve thread-safety, basically to overcome the visibility problem. The variables marked as volatile gets stored in main memory rather than CPU cache.

-          Atomic Variable: Atomic variables are used for performing atomic operations on a single variable instead of a compounded operation, So it solves the synchronization problem ( race condition etc.)

• Java interview questions and answers all MNC - Click here

• Basic core java interview questions and answers for freshers - Click here

• Core java interview questions for 3 years experience - Click here

• Core java interview questions and answers for 3-5 years exp - Click here

• Core java interview questions and Answers for 5 - 7 Years exp - Click here

• Basic Java Interview Questions and Answers - Click here

• Java interview questions and answers on oops - Click here

• Java interview questions and answers on Strings - Click here

• Java interview questions on exception handling - Click here

• Interview questions on multithreading in java for experienced - Click here

• Interview questions on serialization in java for experienced - Click here

• Interview questions on inner class in java for experienced - Click here

• Interview questions on Collections in java for experienced - Click here

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