Multi Threading is a process of running multiple thread at a same time consuming less memory and high performance.

what do you mean by Thread?

Thread is subset of process or lightweight sub-process
or
Threads can be used to perform complicated tasks in the background without interrupting the main program.

Difference between Thread and Process?

How to create Thread in application? Define different way of creating it?

Thread can be created in to two ways:

Extends Thread class

public class CreatingThread extends Thread{
            public void run() {
              System.out.println("Run Method using Thread class");
            }
           
           public static void main(String[] args) {
             CreatingThread thread = new CreatingThread();
             thread.start();
           }
         }

Implements Runnable interface

public class CreatingThread implements Runnable {
          public void run() {
              System.out.println("Run Method implements Runnable");
          }
          public static void main(String[] args) {
              CreatingThread thread = new CreatingThread();
              Thread th = new Thread(thread);
              th.start();
          }
      }

How extend thread and implements Runnable are difference from each other?

Difference between User thread and Demon thread?

How to create Demon thread?

public class DemonNew extends Thread {
          public void run() {
              if (Thread.currentThread().isDaemon() == true) {
                  System.out.println("Demon Thread");
              } else {
                  System.out.println("User Thread");
              }
          }
          public static void main(String[] args) {
              DemonNew t1 = new DemonNew();
              DemonNew t2 = new DemonNew();
              t1.setDaemon(true);
              t1.start();
              t2.start();
          }
      }

Define Thread Scheduler?

Thread Scheduler is a component of Java that decides which thread to run or execute and which thread to wait. Every thread have priority of its own ,if there is more than one thread in the runnable state, it is up to the thread scheduler to pick one of the threads and ignore the other ones. There are two factors for scheduling a thread i.e. Priority and Time of arrival.
Priority: Priority of each thread lies between 1 to 10. Default priority of the thread is 5 If a thread has a higher priority, it means that thread has got a better chance of getting picked up by the thread scheduler.

it can be changed any time after creation. We can check it by getPriority() method or setPriority() method for getting and setting the priority.
Time of Arrival: Suppose two threads of the same priority enter the runnable state, then priority cannot be the factor to pick a thread from these two threads. In such a case, arrival time of thread is considered by the thread scheduler. A thread that arrived first gets the preference over the other threads.

Difference between Preemptive scheduling and Time Slicing?

Difference Stage of Thread life Cycle?

Thread life Cycle have different Stage :

New: when thread is created ,it is in new state until thread call start() method.
Runnable : After starting thread will be in Runnable state until thread scheduler assign priority.
Running: After thread scheduler select thread for running i.e thread is selected for the execution by thread scheduler
Waiting/Block : State of thread is in waiting or block stage for monitor lock .Thread will be in this stage till notify() or notifyAll() method is called
Sleep : In this state thread is waiting at specific time allocated until timeout completed.
Terminated/Dead : Thread after execution completed will be moved to this state.

Difference between Start() and Run() method?

Difference between Wait() and Sleep() method?

Can a thread called twice?

Thread can not be started twice once started can be executed till dead state. If called twice compiler produces runtime exception i.e. IlligalThreadStateException .

Define Join() method ?

Join() method is part of java.lang package.
Java allows one thread to wait until another thread completes its execution. In simpler words, it means it waits for the other thread to die. It has a void type and throws InterruptedException.
Joining threads in Java has three functions namely,

Define Synchronization in Multithreading?

Synchronization is capability of control the access of multiple thread to any shared object resource in order to avoid data inconsistency.
Java Synchronization is better option where we want to allow only one thread to access the shared resource

Why use Synchronization?

The synchronization is mainly used to

Define Deadlock in multithreading?

Deadlock is a situation in which all thread in waiting state are waiting for resource object but non of them get executed .Create universal waiting state and break the code at runtime.

Define between notify() and notifyAll()?

Why Wait() ,notify() and notifyAll() present in Object class?

If wait() and notify() were on the Thread instead then each thread would have to know the status of every other thread and there is no way to know thread1 that thread2 was waiting for any resource to access. Hence, notify, wait, notifyAll methods are defined in object class in Java

why Sleep() and Yeild() method are static by nature ?

Sleep() and Yeild() method are static because it work on currently executing thread, rather than any specific thread – you don’t have to specify which thread is currently running to free up the processor.