The document discusses multithreading in Java. It defines a thread as the smallest unit of processing and describes how Java allows executing multiple threads simultaneously. It outlines the five states in a thread's lifecycle and how threads transition between these states. It also discusses how to create threads by extending the Thread class or implementing the Runnable interface. Additionally, it covers common thread methods like sleep(), join(), getName(), currentThread(), and setting priority. The document concludes with a brief overview of synchronization in Java.

1. MultithreadingMultithreading
By
Nilesh Dalvi
Lecturer, Patkar-Varde College.Lecturer, Patkar-Varde College.
http://www.slideshare.net/nileshdalvi01
Java and Data StructuresJava and Data Structures

2. Introduction
• Multithreading in java is a process of executing
multiple threads simultaneously.
• Thread is basically a lightweight sub-process, a
smallest unit of processing.
• Java Multithreading is mostly used in games,
animation etc.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

3. Thread
• A thread is a light-weight sub process, a smallest unit of
processing. It is a separate path of execution.
• Threads are independent, if there occurs exception in one
thread, it doesn't affect other threads.
• It shares a common memory area.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
t1
t2
t3
Process1
Process2
Process3

4. Life Cycle of Thread
• A thread can be in one of the five states.
• Life cycle of the thread in java is controlled by JVM.
• The java thread states are as follows:
1. New
2. Runnable
3. Running
4. Non-Runnable (Blocked)
5. Terminated
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

5. Life Cycle of Thread
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
NewNew
RunnableRunnable
RunningRunning
TerminatedTerminated
Non-
Runnable
(Blocked)
Non-
Runnable
(Blocked)
start()
run()
Method exits
stop()
run()
Sleep done,
resume, notify
Sleep,
suspend, wait

6. Life Cycle of Thread
1. New state:
– The thread is in new state if you create an instance of
Thread class but before the invocation of start() method.
– It is also referred to as newborn state.
1. Runnable state:
– The thread is in runnable state after invocation of start()
method, but the thread scheduler has not selected it to be
the running thread.
– Thread scheduler: Part of JVM that decides which thread
should run.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

7. Life Cycle of Thread
3. Running state:
– thread is in running state if the thread scheduler has
selected it.
– It has been suspended using suspend() method and
retrieved using resume() method.
– It has been made to sleep using sleep() method for specified
time.
– It has been told to wait until some event occurs, using wait()
method, rescheduled using notify() method.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

8. Life Cycle of Thread
4. Non-Runnable(Blocked) state:
– This is the state when the thread is still alive, but is currently
not eligible to run.
5. Terminated (Dead)state:
– A thread is in terminated or dead state when its run()
method exits.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

9. Creating thread
There are two ways to create a thread:
1. By extending Thread class
2. By implementing Runnable interface.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

10. Thread Class
• Thread class provide constructors and methods to create and
perform operations on a thread.
• Thread class extends Object class and implements Runnable
interface.
• Commonly used constructors:
– Thread()
– Thread(String name)
– Thread(Runnable r)
– Thread(Runnable r, String name)
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

11. Thread Class
Commonly used Method:
•public void run(): is used to perform action for a thread.
•public void start(): starts the execution of the thread. JVM calls the run() method
on the thread.
•public void sleep (long miliseconds): Causes the currently executing thread to sleep
for the specified number of milliseconds.
•public void join(): waits for a thread to die.
•public void join (long miliseconds): waits for a thread to die for the specified
miliseconds.
•public int getPriority(): returns the priority of the thread.
•public int setPriority(int priority): changes the priority of the thread.
•public String getName(): returns the name of the thread.
•public void setName (String name): changes the name of the thread.
•public Thread currentThread(): returns the reference of currently executing thread.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

12. Thread Class
Commonly used Method:
•public int getId(): returns the id of the thread.
•public boolean isAlive(): tests if the thread is alive.
•public void yield(): causes the currently executing thread object to temporarily
pause and allow other threads to execute.
•public void suspend(): is used to suspend the thread(depricated).
•public void resume(): is used to resume the suspended thread(depricated).
•public void stop(): is used to stop the thread(depricated).
•public boolean isDaemon(): tests if the thread is a daemon thread.
•public void setDaemon(boolean b): marks the thread as daemon or user thread.
•public void interrupt(): interrupts the thread.
•public boolean isInterrupted(): tests if the thread has been interrupted.
•public static boolean interrupted(): tests if the current thread has been interrupted.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

13. Extending Thread Class
• It includes following steps:
– Declare the class as extending Thread class.
– Implement the run() method that is responsible for
executing the sequence of code that the thread will execute.
– Create a thread object and call the start() method to initiate
the thread execution.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

14. Extending Thread Class
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class MyThread extends Thread
{
public void run ()
{
System.out.println("Thread Started...!");
for (int count = 1, row = 1; row < 10; row++, count++)
{
for (int i = 0; i < count; i++)
System.out.print ('*');
System.out.print ('n');
}
}
}
class ThreadDemo
{
public static void main (String [] args)
{
MyThread mt = new MyThread ();
mt.start ();
}
}

15. Implementing Runnable interface
• It includes following steps:
– Declare the class as implementing the runnable interface.
– Implement the run() method.
– Create a thread by defining an object that is instantiated
from this runnable class as the target of the thread.
– Call the threads start() method to run the thread.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

16. Implementing Runnable interface
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class MyThread implements Runnable
{
public void run ()
{
System.out.println("Thread Started...!");
for (int count = 1, row = 1; row < 10; row++, count++)
{
for (int i = 0; i < count; i++)
System.out.print ('*');
System.out.print ('n');
}
}
}
class ThreadDemo
{
public static void main (String [] args)
{
MyThread mt = new MyThread ();
Thread t = new Thread (mt);
t.start ();
}
}

17. Sleep()
• sleep() method of Thread class is used to sleep a thread for the
specified milliseconds of time.
• Syntax:
public static void sleep(long miliseconds) throws InterruptedException
public static void sleep(long miliseconds, int nanos) throws InterruptedException
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

18. join()
• join() method waits for a thread to die.
• In other words, it causes the currently running threads to stop
executing until the thread it joins with completes its task.
• Syntax:
public void join()throws InterruptedException
public void join(long milliseconds)throws InterruptedException
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

19. Naming a thread:
• The Thread class provides methods to change and get the name
of a thread.
• public String getName():
– It is used to return the name of a thread.
• public void setName(String name):
– It is used to change the name of a thread.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

20. currentThread()
• currentThread() method returns a reference to the currently
executing thread object.
• Syntax:
public static Thread currentThread():
– returns the reference of currently running thread.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

21. Priority of a Thread (Thread Priority):
• Each thread have a priority.
• Priorities are represented by a number between 1 and 10.
• In most cases, thread scheduler schedules the threads
according to their priority (known as preemptive scheduling).
• But it is not guaranteed because it depends on JVM
specification that which scheduling it chooses.
• 3 constants defined in Thread class:
– public static int MIN_PRIORITY
– public static int NORM_PRIORITY
– public static int MAX_PRIORITY
• Default priority of a thread is 5 (NORM_PRIORITY).
• MIN_PRIORITY is 1 and the value of MAX_PRIORITY is 10.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

22. Performing multiple task by multiple thread
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

23. Synchronization
• Synchronization in java is the capability of control the access of
multiple threads to any shared resource.
• Java Synchronization is better option where we want to allow
only one thread to access the shared resource.
• synchronized method:
– If you declare any method as synchronized, it is known as synchronized
method.
– Synchronized method is used to lock an object for any shared resource.
– When a thread invokes a synchronized method, it automatically acquires
the lock for that object and releases it when the thread completes its
task.
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).

24. Q & A