Multithreading in Java

November 10, 2016 by Manisha Ambekar

Filed under java

Last modified November 10, 2016

Multithreading in java is a process of executing multiple threads simultaneously.Thread is basically a lightweight sub-process, a smallest unit of processing.Multiprocessing and multithreading,both are used to achieve multitasking. But we use multithreading than multiprocessing because threads share a common memory area. They don’t allocate separate memory area so saves memory, and context-switching between the threads takes less time than process.Java is a multi-threaded programming language which means we can develop multi-threaded program using Java.A multi-threaded program contains two or more parts that can run concurrently and each part can handle a different task at the same time making optimal use of the available resources specially when your computer has multiple CPUs.
Multitasking is when multiple processes share common processing resources such as a CPU. Multi-threading extends the idea of multitasking into applications where you can subdivide specific operations within a single application into individual threads. Each of the threads can run in parallel. The OS divides processing time not only among different applications, but also among each thread within an application. Multi-threading enables you to write in a way where multiple activities can proceed concurrently in the same program.

Life Cycle of a Thread
A thread goes through various stages in its life cycle. For example, a thread is born, started, runs, and then dies. The following diagram shows the complete life cycle of a thread



Following are the stages of the life cycle −
• New − A new thread begins its life cycle in the new state. It remains in this state until the program starts the thread. It is also referred to as a born thread.
• Runnable − After a newly born thread is started, the thread becomes runnable. A thread in this state is considered to be executing its task.
• Waiting − Sometimes, a thread transitions to the waiting state while the thread waits for another thread to perform a task. A thread transitions back to the runnable state only when another thread signals the waiting thread to continue executing.
• Timed Waiting − A runnable thread can enter the timed waiting state for a specified interval of time. A thread in this state transitions back to the runnable state when that time interval expires or when the event it is waiting for occurs.
• Terminated (Dead) − A runnable thread enters the terminated state when it completes its task or otherwise terminates.

Thread Priorities
Every Java thread has a priority that helps the operating system determine the order in which threads are scheduled.
Java thread priorities are in the range between MIN_PRIORITY (a constant of 1) and MAX_PRIORITY (a constant of 10). By default, every thread is given priority NORM_PRIORITY (a constant of 5).
Threads with higher priority are more important to a program and should be allocated processor time before lower-priority threads. However, thread priorities cannot guarantee the order in which threads execute and are very much platform dependent.

Thread Methods
Following is the list of important methods available in the Thread class.
Method & Description
1 public void start()
Starts the thread in a separate path of execution, then invokes the run() method on this Thread object.

2 public void run()
If this Thread object was instantiated using a separate Runnable target, the run() method is invoked on that Runnable object.

3 public final void setName(String name)
Changes the name of the Thread object. There is also a getName() method for retrieving the name.

4 public final void setPriority(int priority)
Sets the priority of this Thread object. The possible values are between 1 and 10.

5 public final void setDaemon(boolean on)
A parameter of true denotes this Thread as a daemon thread.

6 public final void join(long millisec)
The current thread invokes this method on a second thread, causing the current thread to block until the second thread terminates or the specified number of milliseconds passes.

7 public void interrupt()
Interrupts this thread, causing it to continue execution if it was blocked for any reason.

8 public final boolean isAlive()
Returns true if the thread is alive, which is any time after the thread has been started but before it runs to completion.

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