Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V5)

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Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V5) 

PrintCharTask.java

class PrintCharTask implements Runnable
{
    private char character;
    private int noOfTimes;

    PrintCharTask(char ch, int n)
    {
        character = ch;
        noOfTimes = n;
    }

    public void run()
    {
        for (int i = 0; i < noOfTimes; i++)
        {
            System.out.println(character + " ");
        }
    }
}

Threadpool.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class Threadpool
{
    public static void main(String[] args)
    {
        System.out.println("Main Thread starts");
        ExecutorService threadExecutor = Executors.newFixedThreadPool(2);
        
        PrintCharTask taskl = new PrintCharTask('*', 5);
        PrintCharTask task2 = new PrintCharTask('S', 5);
        PrintCharTask task3 = new PrintCharTask('M', 5);
        PrintCharTask task4 = new PrintCharTask('N', 5);
        
        threadExecutor.execute(taskl);
        threadExecutor.execute(task2);
        threadExecutor.execute(task3);
        threadExecutor.execute(task4);
        /*
         * Tells the threadExecutor to shutdown. No new task
         * can be accepted but the existing task will
         * continue to finish.
         */
        threadExecutor.shutdown();
        /*
         * In order to ensure that the main thread finishes
         * last i.e. all tasks are finished before the main
         * thread terminates, we put the below while
         * statement.
         */
        while (!threadExecutor.isTerminated())
        {
        }
        System.out.println("\nMain Thread Ends");
    }
}

Output

Main Thread starts
* 
* 
* 
* 
* 
M 
M 
M 
M 
M 
N 
N 
N 
N 
N 
S 
S 
S 
S 
S 

Main Thread Ends

Click the below link to download the code:
https://sites.google.com/site/ramj2eev1/home/javabasics/ThreadDemo_ThreadPool_V5_App.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/Java/tree/master/BasicJava/ThreadDemo_ThreadPool_V5_App

Bitbucket Link:
https://bitbucket.org/ramram43210/java/src/d6d97a164a2acde3c2aa603063db8720e3eaea01/BasicJava/ThreadDemo_ThreadPool_V5_App/?at=master

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Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V4)

Click here to watch in Youtube :
https://www.youtube.com/watch?v=opOyoZ1mTbE&list=UUhwKlOVR041tngjerWxVccw

Click the below Image to Enlarge

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V4) 

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V4) 

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V4) 

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V4) 

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V4) 

SimpleThreadPool.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class SimpleThreadPool
{

    public static void main(String[] args)
    {
        ExecutorService executor = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 10; i++)
        {
            Runnable runnableTask = new RunnableTask(" " + i);
            executor.execute(runnableTask);
        }
        executor.shutdown();
        while (!executor.isTerminated())
        {
        }
        System.out.println("Finished all threads");
    }
}

RunnableTask.java

public class RunnableTask implements Runnable
{

    private String taskNumber;

    public RunnableTask(String taskNumber)
    {
        this.taskNumber = taskNumber;
    }

    @Override
    public void run()
    {
        System.out.println(Thread.currentThread().getName()
                + " Start. taskNumber = " + taskNumber);
        processCommand();
        System.out.println(Thread.currentThread().getName()
                + " End of taskNumber =" + taskNumber);
    }

    private void processCommand()
    {
        try
        {
            Thread.sleep(5000);
        }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
    }

    @Override
    public String toString()
    {
        return this.taskNumber;
    }
}

Output

pool-1-thread-2 Start. taskNumber =  1
pool-1-thread-4 Start. taskNumber =  3
pool-1-thread-3 Start. taskNumber =  2
pool-1-thread-1 Start. taskNumber =  0
pool-1-thread-5 Start. taskNumber =  4
pool-1-thread-2 End of taskNumber = 1
pool-1-thread-2 Start. taskNumber =  5
pool-1-thread-4 End of taskNumber = 3
pool-1-thread-4 Start. taskNumber =  6
pool-1-thread-1 End of taskNumber = 0
pool-1-thread-1 Start. taskNumber =  7
pool-1-thread-5 End of taskNumber = 4
pool-1-thread-5 Start. taskNumber =  8
pool-1-thread-3 End of taskNumber = 2
pool-1-thread-3 Start. taskNumber =  9
pool-1-thread-4 End of taskNumber = 6
pool-1-thread-2 End of taskNumber = 5
pool-1-thread-3 End of taskNumber = 9
pool-1-thread-1 End of taskNumber = 7
pool-1-thread-5 End of taskNumber = 8
Finished all threads

Refer:
https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html

Click the below link to download the code:
https://sites.google.com/site/ramj2eev1/home/javabasics/ThreadDemo_ThreadPool_V3_App.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/Java/tree/master/BasicJava/ThreadDemo_ThreadPool_V3_App

Bitbucket Link:
https://bitbucket.org/ramram43210/java/src/d6d97a164a2acde3c2aa603063db8720e3eaea01/BasicJava/ThreadDemo_ThreadPool_V3_App/?at=master

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Java Collection Framework Tutorial

JAVA Tutorial

Kids Tutorial

Java Tutorial: Java Threads (Thread pool executor | Thread pool in java | Java thread pool)

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Introduction

Creating a new operating system thread for every incoming task in Java incurs significant memory and CPU overhead. A Thread Pool solves this problem by maintaining a pool of pre-created, reusable worker threads that execute tasks asynchronously from a blocking queue.

In this guide, you will learn how the ThreadPoolExecutor and the java.util.concurrent.Executors framework simplify multithreading, optimize system resource utilization, and improve application throughput.

1. Create a Runnable Task

Define a task by implementing the Runnable interface to represent the work to be executed by worker threads:

public class WorkerTask implements Runnable {
    private final String taskName;

    public WorkerTask(String taskName) {
        this.taskName = taskName;
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + " executing " + taskName);
        try {
            Thread.sleep(1000); // Simulate work
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
        System.out.println(Thread.currentThread().getName() + " completed " + taskName);
    }
}
  

2. Initialize and Submit Tasks to ExecutorService

Create a fixed-size thread pool using the Executors factory class and submit multiple tasks for execution:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ThreadPoolDemo {
    public static void main(String[] args) {
        // Create a thread pool with 3 worker threads
        ExecutorService executor = Executors.newFixedThreadPool(3);

        // Submit 6 tasks to the pool
        for (int i = 1; i <= 6; i++) {
            executor.execute(new WorkerTask("Task-" + i));
        }

        // Shut down the executor gracefully after completion
        executor.shutdown();
    }
}
  

3. Key Advantages of Using Thread Pools

• Resource Management: Prevents system degradation caused by creating too many threads simultaneously.
• Better Performance: Eliminates thread creation and teardown latency by reusing existing threads.
• Task Queueing: Safely buffers excess tasks in internal blocking queues until threads become available.

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Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V3)

Click here to watch in Youtube :
https://www.youtube.com/watch?v=Zm72Egs_s-Q&list=UUhwKlOVR041tngjerWxVccw

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Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V3)

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V3)

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V3)

SimpleThreadPool.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class SimpleThreadPool
{

    public static void main(String[] args)
    {
        ExecutorService executor = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 10; i++)
        {
            Runnable runnableTask = new RunnableTask(" " + i);
            executor.execute(runnableTask);
        }
        executor.shutdown();
        while (!executor.isTerminated())
        {
        }
        System.out.println("Finished all threads");
    }
}

RunnableTask.java

public class RunnableTask implements Runnable
{

    private String taskNumber;

    public RunnableTask(String taskNumber)
    {
        this.taskNumber = taskNumber;
    }

    @Override
    public void run()
    {
        System.out.println(Thread.currentThread().getName()
                + " Start. taskNumber = " + taskNumber);
        processCommand();
        System.out.println(Thread.currentThread().getName()
                + " End of taskNumber =" + taskNumber);
    }

    private void processCommand()
    {
        try
        {
            Thread.sleep(5000);
        }
        catch (InterruptedException e)
        {
            e.printStackTrace();
        }
    }

    @Override
    public String toString()
    {
        return this.taskNumber;
    }
}

Output

pool-1-thread-2 Start. taskNumber =  1
pool-1-thread-4 Start. taskNumber =  3
pool-1-thread-3 Start. taskNumber =  2
pool-1-thread-1 Start. taskNumber =  0
pool-1-thread-5 Start. taskNumber =  4
pool-1-thread-2 End of taskNumber = 1
pool-1-thread-2 Start. taskNumber =  5
pool-1-thread-4 End of taskNumber = 3
pool-1-thread-4 Start. taskNumber =  6
pool-1-thread-1 End of taskNumber = 0
pool-1-thread-1 Start. taskNumber =  7
pool-1-thread-5 End of taskNumber = 4
pool-1-thread-5 Start. taskNumber =  8
pool-1-thread-3 End of taskNumber = 2
pool-1-thread-3 Start. taskNumber =  9
pool-1-thread-4 End of taskNumber = 6
pool-1-thread-2 End of taskNumber = 5
pool-1-thread-3 End of taskNumber = 9
pool-1-thread-1 End of taskNumber = 7
pool-1-thread-5 End of taskNumber = 8
Finished all threads

Refer: 
https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html

Click the below link to download the code:
https://sites.google.com/site/ramj2eev1/home/javabasics/ThreadDemo_ThreadPool_V3_App.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/Java/tree/master/BasicJava/ThreadDemo_ThreadPool_V3_App

Bitbucket Link:
https://bitbucket.org/ramram43210/java/src/d6d97a164a2acde3c2aa603063db8720e3eaea01/BasicJava/ThreadDemo_ThreadPool_V3_App/?at=master

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Java Collection Framework Tutorial

JAVA Tutorial

Kids Tutorial

Java Tutorial: Java Threads (Java Thread pool types | Thread pool in java | Java thread pool)

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Java Tutorial: Java Threads (Java Thread pool types | Thread pool in java | Java thread pool) 

Java Tutorial: Java Threads (Java Thread pool types | Thread pool in java | Java thread pool) 

Java Tutorial: Java Threads (Java Thread pool types | Thread pool in java | Java thread pool) 

Refer: 

https://docs.oracle.com/javase/8/docs/api/index.html?java/util/concurrent/Executors.html

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ThreadPoolExecutor.html

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ScheduledThreadPoolExecutor.html

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Servlets Tutorial

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Java Collection Framework Tutorial

JAVA Tutorial

Kids Tutorial

Java Tutorial: Java Threads (Cached Thread pool in java | Java cached thread pool)

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https://www.youtube.com/watch?v=wOqI-EeUWVE&list=UUhwKlOVR041tngjerWxVccw

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Java Tutorial: Java Threads (Cached Thread pool in java | Java cached thread pool) 

Java Tutorial: Java Threads (Cached Thread pool in java | Java cached thread pool) 

ThreadPoolTest.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class ThreadPoolTest
{
    public static void main(String[] args)
    {
        int numOfCallableTasks = 4;

        ExecutorService executorService = Executors.newCachedThreadPool();
        CallableTask callableTasks[] = new CallableTask[numOfCallableTasks];
        Future<?> futures[] = new Future[numOfCallableTasks];

        for (int i = 0; i < numOfCallableTasks; i++)
        {
            callableTasks[i] = new CallableTask(i);
            futures[i] = executorService.submit(callableTasks[i]);
        }
        for (int i = 0; i < numOfCallableTasks; i++)
        {
            try
            {
                System.out.println("Ending task : " + futures[i].get());
            }
            catch (Exception e)
            {
                e.printStackTrace();
            }
        }
    }
}

CallableTask.java

import java.util.concurrent.Callable;

public class CallableTask implements Callable<Integer>
{
    private int taskNumber;

    CallableTask(int taskNumber)
    {
        this.taskNumber = taskNumber;
    }

    public Integer call()
    {
        for (int i = 0; i <= 100; i += 20)
        {
            // Perform some work ...
            System.out.println(Thread.currentThread().getName()
                    + " taskNumber : " + taskNumber + ", percent complete: "
                    + i);
            try
            {
                Thread.sleep((int) (Math.random() * 1000));
            }
            catch (InterruptedException e)
            {
            }
        }
        return (taskNumber);
    }
}

Output

pool-1-thread-2 taskNumber : 1, percent complete: 0
pool-1-thread-1 taskNumber : 0, percent complete: 0
pool-1-thread-3 taskNumber : 2, percent complete: 0
pool-1-thread-4 taskNumber : 3, percent complete: 0
pool-1-thread-2 taskNumber : 1, percent complete: 20
pool-1-thread-4 taskNumber : 3, percent complete: 20
pool-1-thread-1 taskNumber : 0, percent complete: 20
pool-1-thread-3 taskNumber : 2, percent complete: 20
pool-1-thread-4 taskNumber : 3, percent complete: 40
pool-1-thread-3 taskNumber : 2, percent complete: 40
pool-1-thread-2 taskNumber : 1, percent complete: 40
pool-1-thread-4 taskNumber : 3, percent complete: 60
pool-1-thread-3 taskNumber : 2, percent complete: 60
pool-1-thread-2 taskNumber : 1, percent complete: 60
pool-1-thread-1 taskNumber : 0, percent complete: 40
pool-1-thread-2 taskNumber : 1, percent complete: 80
pool-1-thread-3 taskNumber : 2, percent complete: 80
pool-1-thread-2 taskNumber : 1, percent complete: 100
pool-1-thread-4 taskNumber : 3, percent complete: 80
pool-1-thread-1 taskNumber : 0, percent complete: 60
pool-1-thread-4 taskNumber : 3, percent complete: 100
pool-1-thread-3 taskNumber : 2, percent complete: 100
pool-1-thread-1 taskNumber : 0, percent complete: 80
pool-1-thread-1 taskNumber : 0, percent complete: 100
Ending task : 0
Ending task : 1
Ending task : 2
Ending task : 3

Click the below link to download the code:
https://sites.google.com/site/ramj2eev1/home/javabasics/ThreadDemo_CachedThreadPool_App.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/Java/tree/master/BasicJava/ThreadDemo_CachedThreadPool_App

Bitbucket Link:
https://bitbucket.org/ramram43210/java/src/0fa116261fbf2fe2bc94946e6ef3f543aabbf896/BasicJava/ThreadDemo_CachedThreadPool_App/?at=master

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Kids Tutorial

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V2)

Click here to watch in Youtube :
https://www.youtube.com/watch?v=dy1uAsZOvC0&list=UUhwKlOVR041tngjerWxVccw

Click the below Image to Enlarge

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V2) 

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V2) 

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V2) 

Java Tutorial: Java Threads (Thread pool in java | Java thread pool | Java thread pool tutorial_V2) 

ThreadPoolTest.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ThreadPoolTest
{

    public static void main(String[] args)
    {
        int numRunnableTask = 4;
        int threadPoolSize = 2;

        ExecutorService tpes = Executors.newFixedThreadPool(threadPoolSize);

        RunnableTask[] runnableTasks = new RunnableTask[numRunnableTask];
        for (int i = 0; i < numRunnableTask; i++)
        {
            runnableTasks[i] = new RunnableTask(i);
            tpes.execute(runnableTasks[i]);
        }
        tpes.shutdown();
    }
}

RunnableTask.java

/*
 * Here is a runnable task. This task performs some work and
 * then periodically reports what percent of the work it has
 * completed:
 */

public class RunnableTask implements Runnable
{
    private int taskNumber;

    public RunnableTask(int taskNumber)
    {
        this.taskNumber = taskNumber;
    }

    public void run()
    {
        for (int i = 0; i <= 100; i += 20)
        {
            // Perform some work ...
            System.out.println(Thread.currentThread().getName()
                    + " = RunnableTask number: " + taskNumber
                    + ", percent complete: " + i);
            try
            {
                Thread.sleep(3000);
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }
}

Output

pool-1-thread-1 = RunnableTask number: 0, percent complete: 0
pool-1-thread-2 = RunnableTask number: 1, percent complete: 0
pool-1-thread-1 = RunnableTask number: 0, percent complete: 20
pool-1-thread-2 = RunnableTask number: 1, percent complete: 20
pool-1-thread-2 = RunnableTask number: 1, percent complete: 40
pool-1-thread-1 = RunnableTask number: 0, percent complete: 40
pool-1-thread-1 = RunnableTask number: 0, percent complete: 60
pool-1-thread-2 = RunnableTask number: 1, percent complete: 60
pool-1-thread-1 = RunnableTask number: 0, percent complete: 80
pool-1-thread-2 = RunnableTask number: 1, percent complete: 80
pool-1-thread-1 = RunnableTask number: 0, percent complete: 100
pool-1-thread-2 = RunnableTask number: 1, percent complete: 100
pool-1-thread-2 = RunnableTask number: 2, percent complete: 0
pool-1-thread-1 = RunnableTask number: 3, percent complete: 0
pool-1-thread-2 = RunnableTask number: 2, percent complete: 20
pool-1-thread-1 = RunnableTask number: 3, percent complete: 20
pool-1-thread-1 = RunnableTask number: 3, percent complete: 40
pool-1-thread-2 = RunnableTask number: 2, percent complete: 40
pool-1-thread-1 = RunnableTask number: 3, percent complete: 60
pool-1-thread-2 = RunnableTask number: 2, percent complete: 60
pool-1-thread-2 = RunnableTask number: 2, percent complete: 80
pool-1-thread-1 = RunnableTask number: 3, percent complete: 80
pool-1-thread-1 = RunnableTask number: 3, percent complete: 100
pool-1-thread-2 = RunnableTask number: 2, percent complete: 100

Refer: 
https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html

Click the below link to download the code:
https://sites.google.com/site/ramj2eev1/home/javabasics/ThreadDemo_ThreadPool_V2_App.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/Java/tree/master/BasicJava/ThreadDemo_ThreadPool_V2_App

Bitbucket Link:
https://bitbucket.org/ramram43210/java/src/0fa116261fbf2fe2bc94946e6ef3f543aabbf896/BasicJava/ThreadDemo_ThreadPool_V2_App/?at=master

See also:

All JavaEE Viedos Playlist

All JavaEE Viedos

All JAVA EE Links

Servlets Tutorial

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JDBC Tutorial

Java Collection Framework Tutorial

JAVA Tutorial

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