Interview questions on multithreading in java for experienced

 Part 4

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

    What will happen if I am trying to run a thread which is already in running the state?

-     Yes, we can't start already running thread. It will throw IllegalThreadStateException at runtime - if the thread was already started.

-       For your reference please refer to the below example.

package simplifiedjava.crackedInterview;  public class RestartedThreadDemo extends Thread{        @Override       public void run() {                 }                public static void main(String[] args) {             Thread t = new Thread();             t.start();             t.start();              } }  Output: Exception in thread "main" java.lang.IllegalThreadStateException        at java.lang.Thread.start(Unknown Source)        at simplifiedjava.crackedInterview.RestartedThreadDemo.main (RestartedThreadDemo.java:14)

 

    Can we convert a normal thread into a daemon thread once the thread started or not started in both cases?

-          Yes, we can convert a normal thread into a daemon thread.

-          Daemon thread is a very lightweight thread.

-          But, a Normal thread can convert into a daemon thread but it is not possible after the thread is running state. It is possible before the thread is running state.

-          Normal thread can convert by invoking setDaemon() thread.

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    How do you share the data between two threads?

-          We should declare such variables as static and volatile.

-       Volatile variables are shared across multiple threads. This means that individual threads won’t cache their copy in the thread-local. But every object would have its own copy of the variable so threads may cache value locally.

-          We know that static fields are shared across all the objects of the class, and it belongs to the class and not the individual objects. But, for static and non-volatile variables also, threads may cache the variable locally.

 

    What is the difference between notify and notifyAll()?

-          Notify() method can be used to notify only one thread at a time which is waiting in a waiting state.

-       NotifyAll() method can be used to notify all threads at a time that is waiting in a waiting state.

    What is the difference between preemptive scheduling and time slicing?

	Preemptive Scheduling	Time Slicing
1.	Executes highest priority task executes until it highest priority task comes into existence or thread enters into waiting state or dead state.	Task executes for a predefined slice of time and then reenters into the pool of ready tasks. The scheduler will decide which task needs to execute first according to priority.

 

    What is the difference between interrupted() and isInterrupted() method in java?

	Interrupted()	isInterrupted()
1.	interrupted() method is a static method of class thread checks the current thread and clear the interruption "flag". i.e. a second call to interrupted() will return false.	isInterrupted() method is an instance method; it reports the status of the thread on which it is invoked. it does not clear the interruption flag.
2.	Syntax: if(t.interrupted()) {                   System.out.println("inside interrupted");                   }	Syntax: if(t.isInterrupted()) {                   System.out.println("inside isInterrupted.");                   }

    Why wait(), notify() and notifyAll() method must called/invoke from synchronized area? What will happen if I invoked outside synchronized block?

-  Threads uses wait(), notify() and notifyAll() method for inter-thread communication.

-   Thread can get a lock either synchronized method or synchronized block. Thread must get a lock to call wait(), notify() and notifyAll() method.

-   If you invoke these methods outside the synchronized block or method then you will get IllegalMonitorStateException.

 

    What is context switching?

-   Context switching is a technique or method used by the operating system to switch a process from one state to another to execute its function using CPUs in the system.

-   When context switching performed in the system, it stores the old running process's status in the form of registers and assigns the CPU to a new process to execute its tasks.

-    A context switching helps to share a single CPU across all processes to complete its execution and store the system's tasks status.

-     Context Switching is the process of storing and restoring of CPU state so that Thread execution can be resumed from the same point at a later point of time.

 

    What is blocking queue?

-    A Queue that additionally supports operations that wait for the queue to become non-empty when retrieving an element, and wait for space to become available in the queue when storing an element.

-     A BlockingQueue does not accept null elements.

-   Implementations throw NullPointerException on attempts to add, put or offer a null.

-     A BlockingQueue may be capacity bounded.

-   At any given time it may have a remaining Capacity beyond which no additional elements can be put without blocking. A BlockingQueue without any intrinsic capacity constraints always reports a remaining capacity of Integer.MAX_VALUE.

-   BlockingQueue implementations are designed to be used primarily for producer-consumer queues, but additionally support the Collection interface.

-      BlockingQueue implementations are thread-safe.

 

    How would you check whether Thread holds a lock of object or not?

-  You can identify the lock on the particular object by calling wait() or notify() method on that object. If the object does not hold the lock, then it will throw llegalMonitorStateException.

        -    By calling holdsLock(Object o) method. This will return the boolean value.

• 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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