Multithreading in Java – Learn with Examples

Java is a programming language that supports multithreaded programs. Multithreaded programs accommodate two or more parts (threads) that run simultaneously, handling different tasks, enabling optimal CPU usage. Multi-threading is an extension of multi tasking. Multi tasking can be defined as a feature where multiple processes share a common processing resource like a central processing unit. 

Multithreading branches out the concept of multi-tasking to various applications where defined operations can be broken down into smaller individual threads.

Each of these threads runs simultaneously and independently with different execution paths such that an exception in one thread does not affect the performance of others. 

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What is Multithreading in Java?

Multithreading in Java is where multiple threads are executed simultaneously to maximize the CPU time.

Life Cycle of a Thread

Threads have different stages in their life cycle. They are as follows:

• New: The thread begins its life cycle as a new thread. It remains in this newborn stage until a program runs the thread. 
• Runnable: A born thread enters the runnable stage when a program initiates it. The thread starts executing its task in this stage.
• Waiting: This is a transition stage where a thread waits for another thread to complete its task. A thread in the waiting stage switches to a runnable stage after receiving a signal from other threads.
• Timed waiting: This is a stage that a runnable thread can enter for a specific time interval. Threads in this stage move back to the runnable stage at the end of the specific time interval. 
• Dead: This is the final stage in the life cycle of a thread. A thread enters this stage after completing its task. 

Benefits of Multithreading in Java

• As threads in Java are independent, Java multithreading does not block the users, and they can perform many operations simultaneously. 
• As multithreading in Java enables multiple operations, it is time-saving and efficient. 
• The program can run continuously even if a part of it is intercepted.
• It improves the performance against the conventional parallel programs that use multiple processes.
• Creation of efficient programs that utilize the CPU time to its fullest.
• Greatly improves the response time of complex applications. 
• Requires fewer resources compared to traditional parallel programs.

Order of Thread Priority

The operating system determines the thread’s execution schedule based on the thread’s priority. A thread’s priority is determined based on its constant’s value. 

• Constant 1 gets minimum priority ( MIN_PRIORITY)
• Constant 5 gets normal priority ( NORM_PRIORITY)
• Constant 10 gets the maximum priority (MAX_PRIORITY)

How to create a thread in Java?

Threads can be created in Java in two ways:

1. Extending thread class
2. Implementing a runnable interface

Creating a Thread by Extending Thread Class

A few methods of thread class and their functions are given below. 

• getName() : For obtaining thread’s name
• getPriority(): To obtain thread’s priority
• is Alive(): to find if a thread is running 
• join(): wait for a thread’s termination
• run() : Point of thread’s entry
• sleep(): For suspending a thread for a specific time window.
• start() : To activate a thread through its run() method.

Step 1: Override the run() method given in the thread class. This acts as the entry point for the thread, and the entire program logic should be encased in 4this. 

The syntax of the run() method is as follows:

public void run ( )

Step 2:  Initiate the thread object by start () method whose syntax is a void start ( ). 

Here are examples of a multithreading program in Java:

Example 1:

class MultithreadingDemo extends Thread{  

  public void run(){  

    System.out.println(“My thread is running.”);  

  }   

  public static void main(String args[]){  

     MultithreadingDemo obj=new MultithreadingDemo();   

     obj.start();  

  }  

}

The output of the above program will be:

My thread is running.

Example 2: 

class Count extends Thread

{

   Count()

   {

     super(“my thread is extending”);

     System.out.println(“my thread is created” + this);

     start();

   }

   public void run()

   {

     try

     {

        for (int i=0 ;i<10;i++)

        {

           System.out.println(“Printing the count ” + i);

           Thread.sleep(1000);

        }

     }

     catch(InterruptedException e)

     {

        System.out.println(“my thread got interrupted”);

     }

     System.out.println(“My thread is over” );

   }

}

class ExtendingExample

{

   public static void main(String args[])

   {

      Count cnt = new Count();

      try

      {

         while(cnt.isAlive())

         {

           System.out.println(“Main thread will be alive till the child thread lives”);

           Thread.sleep(1500);

         }

      }

      catch(InterruptedException e)

      {

        System.out.println(“Main thread got interrupted”);

      }

      System.out.println(“Main thread’s run is terminated” );

   }

}

The output of the above program will be 

my thread is createdThread[my runnable thread,5,main]

Main thread will be alive till the child thread lives

Printing the count 0

Printing the count 1

Main thread will be alive till the child thread lives

Printing the count 2

Main thread will be alive till the child thread lives

Printing the count 3

Printing the count 4

Main thread will be alive till the child thread lives

Printing the count 5

Main thread will be alive till the child thread lives

Printing the count 6

Printing the count 7

Main thread will be alive till the child thread lives

Printing the count 8

Main thread will be alive till the child thread lives

Printing the count 9

my thread run is terminated

Main thread run is terminated

Creating a Thread by Implementing a Runnable Interface

There are three important steps to be followed while using this method. 

Step 1: A run() method should be implemented by a runnable interface. This run() method acts as the entry point for the thread and should contain the entire program logic. 

Syntax for the run() method is 

public void run( )

Step 2:  A thread object should be activated using the constructor given below.

Thread(Runnable threadObj, String threadName);

Here threadObj acts as the class that implements the runnable interface, and thread name is the name given to the new thread.

Step 3: After creating the thread object, it can be initiated by the start() method that executes the run() method. 

The syntax of the start () method is as follows.

void start();

An example of creating a thread by implementing a runnable interface can be found here.

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