Multithreading in Java with example
Multithreading in Java
When we want to
run multiple programs or tasks simultaneously is known as multitasking. For
example running VLC, Word, and Browser at a given time is an example of
multitasking. Every program in memory is known as a process and each process
has taken a single unit of time.
- Multiprocessing which is based on process and associated with operating system level.
- Multitasking is based on thread and it is associated with programmer.
What is Thread in java?
A thread is a subpart of a
process which lightweight and it is the smallest sequence of a program or a
process. Each thread has some priority and the higher the priority higher the chances
of executing preference.
The life cycle of thread
The JVM controlled the life cycle of a thread and it has five
states 1. New, 2. Runnable, 3. Running, 4. Non-Runnable (Blocked) and last 5.
Terminated.
How to create a thread in java?
We can thread in java by two method
First, With Thread class extending
and second with implementing Runnable interface.
Java provides predefine API
to implement thread, a few of commonly used API as follows
- thread () Create a new thread
- Thread (Runnable target)
- Thread (String name)
- Thread (Runnable target, String name)
- Thread (ThreadGroup g, Runnable target)
To
create a thread we used two way first by extending Thread class and second by implementing
Runnable interface and this done by overriding the run() method. After then
start() is called.
By implementing Runnable interface
public
class RunnableInteface implements Runnable
{
public void run()
{
System.out.println("thread is
running.. by Runnable interface");
}
public static void main(String args[])
{
RunnableInteface ob=new
RunnableInteface();
Thread t1 =new Thread(ob);
t1.start();
}
}
Output
thread
is running.. by Runnable interface
In the above program, we implement a Runnable interface. And override the run()
method and then create an object of the class and that object passed in the
Thread class constructor as Thread(ob).
By extending class Thread
public
class ExtendingThread extends Thread
{
public void run()
{
System.out.println("thread is
running..by extending class Thread.");
}
public static void main(String args[])
{
ExtendingThread t1=new
ExtendingThread();
t1.start();
}
}
Output
thread
is running..by extending class Thread.
Another example
public class DemoThread
extends Thread
{
public void run()
{
for(int i=0; i<5; i++)
{
System.out.println(getName() +
"i=" + i);
}
}
DemoThread() // constructor
{
start();
}
public static void main(String args[])
{
DemoThread ob1 = new DemoThread();
DemoThread ob2 = new DemoThread();
}
}
In the above program
run() method override and invoked by its constructor method, a loop is run from
0 to 4 and print the thread name with the help of getThread() method. In main()
method two objects are created. It will print the following output
Thread-1 i=0
Thread-1 i=1
Thread-1 i=2
Thread-1 i=3
Thread-1 i=4
Thread-0 i=0
Thread-0 i=1
Thread-0 i=2
Thread-0 i=3
Thread-0 i=4
Difference between Daemon and User Threads
The main difference between Daemon and User threads is, a Daemon thread is low
priority thread and User thread is a high priority thread.
Daemon
thread is used in the background supporting task and User thread is used in the foreground.
Daemon
thread life depends on the User thread whereas User Thread are independent.
Creating of Daemon Thread
public
class Daemon extends Thread {
@Override
public void run()
{
System.out.println("User Thread or
Non-Daemon Thread");
}
}
class
DaemonThread
{
public static void main(String[] args)
{
Daemon daemon = new Daemon();
daemon.start();
System.out.println("Main
Thread");
System.out.println("Is " +
daemon.getName() + " a Daemon Thread: " + daemon.isDaemon());
System.out.println("Is " +
Thread.currentThread().getName() + " a Daemon Thread: "
+ Thread.currentThread().isDaemon());
}
}
Inter-Thread communication
When a process communicates with synchronized threads is known as
inter-thread communication. It is used to check thread pooling in java. This can
be achieved by notify(), notifyAll() and wait() method.
Few points about the thread
- A thread is the smallest unit of execution
- Multiple tasks execution is multitasking from the user perspective and from multithreading from an operating system perspective
- Thread is lightweight
- Thread is a part of the process and it is an instance of a program
- Java thread can be created either by class Thread or by interface Runnable
- in a thread a run() method override
- The start() method automatically invoke the run() method
- The yield method of thread provides a chance to wait for another thread
- join() method is used to wait till the thread finishes its execution
- sleep() method is used to delay in execution
- Suspending a thread can be resume again later on by resuming it
- stop() method stop the thread and make it dead, it can not be resume again
- synchronized can be used to synchronize the thread
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