[BAEL-9555] - Created a core-java-modules folder

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/Scheduledexecutorservice/ScheduledExecutorServiceDemo.java

@@ -0,0 +1,52 @@
+package com.baeldung.concurrent.Scheduledexecutorservice;
+
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
+
+public class ScheduledExecutorServiceDemo {
+
+	private void execute() {
+		ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
+		getTasksToRun().apply(executorService);
+		executorService.shutdown();
+	}
+
+	private void executeWithMultiThread() {
+		ScheduledExecutorService executorService = Executors.newScheduledThreadPool(2);
+		getTasksToRun().apply(executorService);
+		executorService.shutdown();
+	}
+
+	private Function<ScheduledExecutorService, Void> getTasksToRun() {
+		return (executorService -> {
+			ScheduledFuture<?> scheduledFuture1 = executorService.schedule(() -> {
+				// Task
+			}, 1, TimeUnit.SECONDS);
+
+			ScheduledFuture<?> scheduledFuture2 = executorService.scheduleAtFixedRate(() -> {
+				// Task
+			}, 1, 10, TimeUnit.SECONDS);
+
+			ScheduledFuture<?> scheduledFuture3 = executorService.scheduleWithFixedDelay(() -> {
+				// Task
+			}, 1, 10, TimeUnit.SECONDS);
+
+			ScheduledFuture<String> scheduledFuture4 = executorService.schedule(() -> {
+				// Task
+				return "Hellow world";
+			}, 1, TimeUnit.SECONDS);
+			return null;
+		});
+	}
+
+	public static void main(String... args) {
+		ScheduledExecutorServiceDemo demo = new ScheduledExecutorServiceDemo();
+		demo.execute();
+		demo.executeWithMultiThread();
+	}
+
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/callable/FactorialTask.java

@@ -0,0 +1,30 @@
+package com.baeldung.concurrent.callable;
+
+
+import java.util.concurrent.Callable;
+
+public class FactorialTask implements Callable<Integer> {
+    int number;
+
+    public FactorialTask(int number) {
+        this.number = number;
+    }
+
+    public Integer call() throws InvalidParamaterException {
+        int fact=1;
+        if(number < 0)
+            throw new InvalidParamaterException("Number must be positive");
+
+        for(int count=number;count>1;count--){
+            fact=fact * count;
+        }
+
+        return fact;
+    }
+
+    private class InvalidParamaterException extends Exception {
+        public InvalidParamaterException(String message) {
+            super(message);
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/cyclicbarrier/CyclicBarrierExample.java

@@ -0,0 +1,24 @@
+package com.baeldung.concurrent.cyclicbarrier;
+
+import java.util.concurrent.CyclicBarrier;
+
+public class CyclicBarrierExample {
+
+    public void start() {
+        CyclicBarrier cyclicBarrier = new CyclicBarrier(3, () -> {
+            // Task
+            System.out.println("All previous tasks are completed");
+        });
+
+        Thread t1 = new Thread(new Task(cyclicBarrier), "T1");
+        Thread t2 = new Thread(new Task(cyclicBarrier), "T2");
+        Thread t3 = new Thread(new Task(cyclicBarrier), "T3");
+
+        if (!cyclicBarrier.isBroken()) {
+            t1.start();
+            t2.start();
+            t3.start();
+        }
+    }
+}
+

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/cyclicbarrier/Task.java

@@ -0,0 +1,24 @@
+package com.baeldung.concurrent.cyclicbarrier;
+
+import java.util.concurrent.BrokenBarrierException;
+import java.util.concurrent.CyclicBarrier;
+
+public class Task implements Runnable {
+
+    private CyclicBarrier barrier;
+
+    public Task(CyclicBarrier barrier) {
+        this.barrier = barrier;
+    }
+
+    @Override
+    public void run() {
+        try {
+            System.out.println("Thread : " + Thread.currentThread().getName() + " is waiting");
+            barrier.await();
+            System.out.println("Thread : " + Thread.currentThread().getName() + " is released");
+        } catch (InterruptedException | BrokenBarrierException e) {
+            e.printStackTrace();
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/executor/ExecutorDemo.java

@@ -0,0 +1,14 @@
+package com.baeldung.concurrent.executor;
+
+import java.util.concurrent.Executor;
+
+public class ExecutorDemo {
+
+	public void execute() {
+		Executor executor = new Invoker();
+		executor.execute(()->{
+			// task to be performed
+		});
+	}
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/executor/Invoker.java

@@ -0,0 +1,12 @@
+package com.baeldung.concurrent.executor;
+
+import java.util.concurrent.Executor;
+
+public class Invoker implements Executor {
+
+	@Override
+	public void execute(Runnable r) {
+		r.run();
+	}
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/executorservice/DelayedCallable.java

@@ -0,0 +1,39 @@
+package com.baeldung.concurrent.executorservice;
+
+import java.util.concurrent.Callable;
+import java.util.concurrent.CountDownLatch;
+
+public class DelayedCallable implements Callable<String> {
+    
+    private String name;
+    private long period;
+    private CountDownLatch latch;
+    
+    public DelayedCallable(String name, long period, CountDownLatch latch) {
+        this(name, period);
+        this.latch = latch;
+    }
+
+    public DelayedCallable(String name, long period) {
+        this.name = name;
+        this.period = period;
+    }
+
+    public String call() {
+
+        try {
+            Thread.sleep(period);
+            
+            if (latch != null) {
+                latch.countDown();
+            }
+            
+        } catch (InterruptedException ex) {
+            // handle exception
+            ex.printStackTrace();
+            Thread.currentThread().interrupt();
+        }
+
+        return name;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/executorservice/ExecutorServiceDemo.java

@@ -0,0 +1,27 @@
+package com.baeldung.concurrent.executorservice;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+public class ExecutorServiceDemo {
+
+    ExecutorService executor = Executors.newFixedThreadPool(10);
+
+    public void execute() {
+
+        executor.submit(() -> {
+            new Task();
+        });
+
+        executor.shutdown();
+        executor.shutdownNow();
+        try {
+            executor.awaitTermination(20l, TimeUnit.NANOSECONDS);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/executorservice/Task.java

@@ -0,0 +1,10 @@
+package com.baeldung.concurrent.executorservice;
+
+public class Task implements Runnable {
+
+	@Override
+	public void run() {
+		// task details
+	}
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/future/FactorialSquareCalculator.java

@@ -0,0 +1,26 @@
+package com.baeldung.concurrent.future;
+
+import java.util.concurrent.RecursiveTask;
+
+public class FactorialSquareCalculator extends RecursiveTask<Integer> {
+    private static final long serialVersionUID = 1L;
+
+    final private Integer n;
+
+    FactorialSquareCalculator(Integer n) {
+        this.n = n;
+    }
+
+    @Override
+    protected Integer compute() {
+        if (n <= 1) {
+            return n;
+        }
+
+        FactorialSquareCalculator calculator = new FactorialSquareCalculator(n - 1);
+
+        calculator.fork();
+
+        return n * n + calculator.join();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/future/FutureDemo.java

@@ -0,0 +1,44 @@
+package com.baeldung.concurrent.future;
+
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+public class FutureDemo {
+
+    public String invoke() {
+
+        String str = null;
+
+        ExecutorService executorService = Executors.newFixedThreadPool(10);
+
+        Future<String> future = executorService.submit(() -> {
+            // Task
+            Thread.sleep(10000l);
+            return "Hellow world";
+        });
+
+        future.cancel(false);
+
+        try {
+            future.get(20, TimeUnit.SECONDS);
+        } catch (InterruptedException | ExecutionException | TimeoutException e1) {
+            e1.printStackTrace();
+        }
+
+        if (future.isDone() && !future.isCancelled()) {
+            try {
+                str = future.get();
+            } catch (InterruptedException | ExecutionException e) {
+                e.printStackTrace();
+            }
+        }
+
+        return str;
+
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/future/SquareCalculator.java

@@ -0,0 +1,20 @@
+package com.baeldung.concurrent.future;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+
+class SquareCalculator {
+
+    private final ExecutorService executor;
+
+    SquareCalculator(ExecutorService executor) {
+        this.executor = executor;
+    }
+
+    Future<Integer> calculate(Integer input) {
+        return executor.submit(() -> {
+            Thread.sleep(1000);
+            return input * input;
+        });
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/runnable/EventLoggingTask.java

@@ -0,0 +1,17 @@
+package com.baeldung.concurrent.runnable;
+
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class EventLoggingTask implements  Runnable{
+    private Logger logger = LoggerFactory.getLogger(EventLoggingTask.class);
+
+    @Override
+    public void run() {
+
+        String messge="Message read from the event queue";
+        logger.info("Message read from event queue is "+messge);
+
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/runnable/TaskRunner.java

@@ -0,0 +1,25 @@
+package com.baeldung.concurrent.runnable;
+
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+
+public class TaskRunner {
+
+    private static ExecutorService executorService;
+
+    public static void main(String[] args) {
+        executeTask();
+    }
+
+    private static void executeTask() {
+        executorService= Executors.newSingleThreadExecutor();
+
+        EventLoggingTask task = new EventLoggingTask();
+
+        Future future = executorService.submit(task);
+
+        executorService.shutdown();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/semaphore/SemaPhoreDemo.java

@@ -0,0 +1,22 @@
+package com.baeldung.concurrent.semaphore;
+
+import java.util.concurrent.Semaphore;
+
+public class SemaPhoreDemo {
+
+	static Semaphore semaphore = new Semaphore(10);
+	
+	public void execute() throws InterruptedException {
+
+		System.out.println("Available permit : " + semaphore.availablePermits());
+		System.out.println("Number of threads waiting to acquire: " + semaphore.getQueueLength());
+
+		if (semaphore.tryAcquire()) {
+			semaphore.acquire();
+			// perform some critical operations
+			semaphore.release();
+		}
+
+	}
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/sleepwait/ThreadA.java

@@ -0,0 +1,27 @@
+package com.baeldung.concurrent.sleepwait;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/***
+ * Example of waking up a waiting thread
+ */
+public class ThreadA {
+
+    private static final Logger LOG = LoggerFactory.getLogger(ThreadA.class);
+
+    private static final ThreadB b = new ThreadB();
+
+    public static void main(String... args) throws InterruptedException {
+        b.start();
+
+        synchronized (b) {
+            while (b.sum == 0) {
+                LOG.debug("Waiting for ThreadB to complete...");
+                b.wait();
+            }
+
+            LOG.debug("ThreadB has completed. Sum from that thread is: " + b.sum);
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/sleepwait/ThreadB.java

@@ -0,0 +1,20 @@
+package com.baeldung.concurrent.sleepwait;
+
+/***
+ * Example of waking up a waiting thread
+ */
+class ThreadB extends Thread {
+    int sum;
+
+    @Override
+    public void run() {
+        synchronized (this) {
+            int i = 0;
+            while (i < 100000) {
+                sum += i;
+                i++;
+            }
+            notify();
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/sleepwait/WaitSleepExample.java

@@ -0,0 +1,29 @@
+package com.baeldung.concurrent.sleepwait;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/***
+ * Example of wait() and sleep() methods
+ */
+public class WaitSleepExample {
+
+    private static final Logger LOG = LoggerFactory.getLogger(WaitSleepExample.class);
+
+    private static final Object LOCK = new Object();
+
+    public static void main(String... args) throws InterruptedException {
+        sleepWaitInSynchronizedBlocks();
+    }
+
+    private static void sleepWaitInSynchronizedBlocks() throws InterruptedException {
+        Thread.sleep(1000); // called on the thread
+        LOG.debug("Thread '" + Thread.currentThread().getName() + "' is woken after sleeping for 1 second");
+
+        synchronized (LOCK) {
+            LOCK.wait(1000); // called on the object, synchronization required
+            LOG.debug("Object '" + LOCK + "' is woken after waiting for 1 second");
+        }
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/stopping/ControlSubThread.java

@@ -0,0 +1,53 @@
+package com.baeldung.concurrent.stopping;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+public class ControlSubThread implements Runnable {
+
+    private Thread worker;
+    private int interval = 100;
+    private AtomicBoolean running = new AtomicBoolean(false);
+    private AtomicBoolean stopped = new AtomicBoolean(true);
+
+
+    public ControlSubThread(int sleepInterval) {
+        interval = sleepInterval;
+    }
+
+    public void start() {
+        worker = new Thread(this);
+        worker.start();
+    }
+
+    public void stop() {
+        running.set(false);
+    }
+
+    public void interrupt() {
+        running.set(false);
+        worker.interrupt();
+    }
+
+    boolean isRunning() {
+        return running.get();
+    }
+
+    boolean isStopped() {
+        return stopped.get();
+    }
+
+    public void run() {
+        running.set(true);
+        stopped.set(false);
+        while (running.get()) {
+            try {
+                Thread.sleep(interval);
+            } catch (InterruptedException e) {
+            	Thread.currentThread().interrupt();
+                System.out.println("Thread was interrupted, Failed to complete operation");
+	    }
+            // do something
+        }
+        stopped.set(true);
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/synchronize/BaeldungSynchronizedBlocks.java

@@ -0,0 +1,35 @@
+package com.baeldung.concurrent.synchronize;
+
+public class BaeldungSynchronizedBlocks {
+
+    private int count = 0;
+    private static int staticCount = 0;
+
+    void performSynchronisedTask() {
+        synchronized (this) {
+            setCount(getCount() + 1);
+        }
+    }
+
+    static void performStaticSyncTask() {
+        synchronized (BaeldungSynchronizedBlocks.class) {
+            setStaticCount(getStaticCount() + 1);
+        }
+    }
+
+    public int getCount() {
+        return count;
+    }
+
+    public void setCount(int count) {
+        this.count = count;
+    }
+
+    static int getStaticCount() {
+        return staticCount;
+    }
+
+    private static void setStaticCount(int staticCount) {
+        BaeldungSynchronizedBlocks.staticCount = staticCount;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/synchronize/BaeldungSynchronizedMethods.java

@@ -0,0 +1,37 @@
+package com.baeldung.concurrent.synchronize;
+
+public class BaeldungSynchronizedMethods {
+
+    private int sum = 0;
+    private int syncSum = 0;
+
+    static int staticSum = 0;
+
+    void calculate() {
+        setSum(getSum() + 1);
+    }
+
+    synchronized void synchronisedCalculate() {
+        setSyncSum(getSyncSum() + 1);
+    }
+
+    static synchronized void syncStaticCalculate() {
+        staticSum = staticSum + 1;
+    }
+
+    public int getSum() {
+        return sum;
+    }
+
+    public void setSum(int sum) {
+        this.sum = sum;
+    }
+
+    int getSyncSum() {
+        return syncSum;
+    }
+
+    private void setSyncSum(int syncSum) {
+        this.syncSum = syncSum;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadfactory/BaeldungThreadFactory.java

@@ -0,0 +1,23 @@
+package com.baeldung.concurrent.threadfactory;
+
+import java.util.concurrent.ThreadFactory;
+
+public class BaeldungThreadFactory implements ThreadFactory {
+
+    private int threadId;
+    private String name;
+
+    public BaeldungThreadFactory(String name) {
+        threadId = 1;
+        this.name = name;
+    }
+
+    @Override
+    public Thread newThread(Runnable r) {
+        Thread t = new Thread(r, name + "-Thread_" + threadId);
+        System.out.println("created new thread with id : " + threadId + " and name : " + t.getName());
+        threadId++;
+        return t;
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadfactory/Demo.java

@@ -0,0 +1,13 @@
+package com.baeldung.concurrent.threadfactory;
+
+public class Demo {
+
+	public void execute() {
+		BaeldungThreadFactory factory = new BaeldungThreadFactory("BaeldungThreadFactory");
+		for (int i = 0; i < 10; i++) {
+			Thread t = factory.newThread(new Task());
+			t.start();
+		}
+	}
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadfactory/Task.java

@@ -0,0 +1,10 @@
+package com.baeldung.concurrent.threadfactory;
+
+public class Task implements Runnable {
+
+    @Override
+    public void run() {
+        // task details
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadlifecycle/BlockedState.java

@@ -0,0 +1,31 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class BlockedState {
+    public static void main(String[] args) throws InterruptedException {
+        Thread t1 = new Thread(new DemoThreadB());
+        Thread t2 = new Thread(new DemoThreadB());
+        
+        t1.start();
+        t2.start();
+        
+        Thread.sleep(1000);
+        
+        System.out.println(t2.getState());
+        System.exit(0);
+    }
+}
+
+class DemoThreadB implements Runnable {
+    @Override
+    public void run() {
+        commonResource();
+    }
+    
+    public static synchronized void commonResource() {
+        while(true) {
+            // Infinite loop to mimic heavy processing
+            // Thread 't1' won't leave this method
+            // when Thread 't2' enters this
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadlifecycle/NewState.java

@@ -0,0 +1,14 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class NewState implements Runnable {
+    public static void main(String[] args) {
+        Runnable runnable = new NewState();
+        Thread t = new Thread(runnable);
+        System.out.println(t.getState());
+    }
+    
+    @Override
+    public void run() {
+        
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadlifecycle/RunnableState.java

@@ -0,0 +1,15 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class RunnableState implements Runnable {
+    public static void main(String[] args) {
+        Runnable runnable = new NewState();
+        Thread t = new Thread(runnable);
+        t.start();
+        System.out.println(t.getState());
+    }
+    
+    @Override
+    public void run() {
+        
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadlifecycle/TerminatedState.java

@@ -0,0 +1,15 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class TerminatedState implements Runnable {
+    public static void main(String[] args) throws InterruptedException {
+        Thread t1 = new Thread(new TerminatedState());
+        t1.start();
+        Thread.sleep(1000);
+        System.out.println(t1.getState());
+    }
+    
+    @Override
+    public void run() {
+        // No processing in this block
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadlifecycle/TimedWaitingState.java

@@ -0,0 +1,25 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class TimedWaitingState {
+    public static void main(String[] args) throws InterruptedException {
+        DemoThread obj1 = new DemoThread();
+        Thread t1 = new Thread(obj1);
+        t1.start();
+        // The following sleep will give enough time for ThreadScheduler
+        // to start processing of thread t1
+        Thread.sleep(1000);
+        System.out.println(t1.getState());
+    }
+}
+
+class DemoThread implements Runnable {
+    @Override
+    public void run() {
+        try {
+            Thread.sleep(5000);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            e.printStackTrace();
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadlifecycle/WaitingState.java

@@ -0,0 +1,35 @@
+package com.baeldung.concurrent.threadlifecycle;
+
+public class WaitingState implements Runnable {
+    public static Thread t1;
+
+    public static void main(String[] args) {
+        t1 = new Thread(new WaitingState());
+        t1.start();
+    }
+
+    public void run() {
+        Thread t2 = new Thread(new DemoThreadWS());
+        t2.start();
+
+        try {
+            t2.join();
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            e.printStackTrace();
+        }
+    }
+}
+
+class DemoThreadWS implements Runnable {
+    public void run() {
+        try {
+            Thread.sleep(1000);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            e.printStackTrace();
+        }
+        
+        System.out.println(WaitingState.t1.getState());
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/application/Application.java

@@ -0,0 +1,86 @@
+package com.baeldung.concurrent.threadsafety.application;
+
+import com.baeldung.concurrent.threadsafety.callables.AtomicCounterCallable;
+import com.baeldung.concurrent.threadsafety.mathutils.MathUtils;
+import com.baeldung.concurrent.threadsafety.callables.CounterCallable;
+import com.baeldung.concurrent.threadsafety.callables.ExtrinsicLockCounterCallable;
+import com.baeldung.concurrent.threadsafety.callables.MessageServiceCallable;
+import com.baeldung.concurrent.threadsafety.callables.ReentranReadWriteLockCounterCallable;
+import com.baeldung.concurrent.threadsafety.callables.ReentrantLockCounterCallable;
+import com.baeldung.concurrent.threadsafety.services.AtomicCounter;
+import com.baeldung.concurrent.threadsafety.services.Counter;
+import com.baeldung.concurrent.threadsafety.services.ExtrinsicLockCounter;
+import com.baeldung.concurrent.threadsafety.services.MessageService;
+import com.baeldung.concurrent.threadsafety.services.ReentrantLockCounter;
+import com.baeldung.concurrent.threadsafety.services.ReentrantReadWriteLockCounter;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.Future;
+
+public class Application {
+    
+    public static void main(String[] args) throws InterruptedException, ExecutionException {
+
+        new Thread(() -> {
+            System.out.println(MathUtils.factorial(10));
+        }).start();
+        new Thread(() -> {
+            System.out.println(MathUtils.factorial(5));
+        }).start();
+        
+        ExecutorService executorService = Executors.newFixedThreadPool(10);
+        MessageService messageService = new MessageService("Welcome to Baeldung!");
+        Future<String> future1 = (Future<String>) executorService.submit(new MessageServiceCallable(messageService));
+        Future<String> future2 = (Future<String>) executorService.submit(new MessageServiceCallable(messageService));
+        System.out.println(future1.get());
+        System.out.println(future2.get());
+        
+        Counter counter = new Counter();
+        Future<Integer> future3 = (Future<Integer>) executorService.submit(new CounterCallable(counter));
+        Future<Integer> future4 = (Future<Integer>) executorService.submit(new CounterCallable(counter));
+        System.out.println(future3.get());
+        System.out.println(future4.get());
+        
+        ExtrinsicLockCounter extrinsicLockCounter = new ExtrinsicLockCounter();
+        Future<Integer> future5 = (Future<Integer>) executorService.submit(new ExtrinsicLockCounterCallable(extrinsicLockCounter));
+        Future<Integer> future6 = (Future<Integer>) executorService.submit(new ExtrinsicLockCounterCallable(extrinsicLockCounter));
+        System.out.println(future5.get());
+        System.out.println(future6.get());
+        
+        ReentrantLockCounter reentrantLockCounter = new ReentrantLockCounter();
+        Future<Integer> future7 = (Future<Integer>) executorService.submit(new ReentrantLockCounterCallable(reentrantLockCounter));
+        Future<Integer> future8 = (Future<Integer>) executorService.submit(new ReentrantLockCounterCallable(reentrantLockCounter));
+        System.out.println(future7.get());
+        System.out.println(future8.get());
+        
+        ReentrantReadWriteLockCounter reentrantReadWriteLockCounter = new ReentrantReadWriteLockCounter();
+        Future<Integer> future9 = (Future<Integer>) executorService.submit(new ReentranReadWriteLockCounterCallable(reentrantReadWriteLockCounter));
+        Future<Integer> future10 = (Future<Integer>) executorService.submit(new ReentranReadWriteLockCounterCallable(reentrantReadWriteLockCounter));
+        System.out.println(future9.get());
+        System.out.println(future10.get());
+        
+        AtomicCounter atomicCounter = new AtomicCounter();
+        Future<Integer> future11 = (Future<Integer>) executorService.submit(new AtomicCounterCallable(atomicCounter));
+        Future<Integer> future12 = (Future<Integer>) executorService.submit(new AtomicCounterCallable(atomicCounter));
+        System.out.println(future11.get());
+        System.out.println(future12.get());
+        
+        Collection<Integer> syncCollection = Collections.synchronizedCollection(new ArrayList<>());
+        Thread thread11 = new Thread(() -> syncCollection.addAll(Arrays.asList(1, 2, 3, 4, 5, 6)));
+        Thread thread12 = new Thread(() -> syncCollection.addAll(Arrays.asList(1, 2, 3, 4, 5, 6)));
+        thread11.start();
+        thread12.start();
+        
+        Map<String,String> concurrentMap = new ConcurrentHashMap<>();
+        concurrentMap.put("1", "one");
+        concurrentMap.put("2", "two");
+        concurrentMap.put("3", "three");
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/callables/AtomicCounterCallable.java

@@ -0,0 +1,19 @@
+package com.baeldung.concurrent.threadsafety.callables;
+
+import com.baeldung.concurrent.threadsafety.services.AtomicCounter;
+import java.util.concurrent.Callable;
+
+public class AtomicCounterCallable implements Callable<Integer> {
+
+    private final AtomicCounter counter;
+    
+    public AtomicCounterCallable(AtomicCounter counter) {
+        this.counter = counter;
+    }
+
+    @Override
+    public Integer call() throws Exception {
+        counter.incrementCounter();
+        return counter.getCounter();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/callables/CounterCallable.java

@@ -0,0 +1,19 @@
+package com.baeldung.concurrent.threadsafety.callables;
+
+import com.baeldung.concurrent.threadsafety.services.Counter;
+import java.util.concurrent.Callable;
+
+public class CounterCallable implements Callable<Integer> {
+
+    private final Counter counter;
+    
+    public CounterCallable(Counter counter) {
+        this.counter = counter;
+    }
+
+    @Override
+    public Integer call() throws Exception {
+        counter.incrementCounter();
+        return counter.getCounter();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/callables/ExtrinsicLockCounterCallable.java

@@ -0,0 +1,19 @@
+package com.baeldung.concurrent.threadsafety.callables;
+
+import com.baeldung.concurrent.threadsafety.services.ExtrinsicLockCounter;
+import java.util.concurrent.Callable;
+
+public class ExtrinsicLockCounterCallable implements Callable<Integer> {
+
+    private final ExtrinsicLockCounter counter;
+    
+    public ExtrinsicLockCounterCallable(ExtrinsicLockCounter counter) {
+        this.counter = counter;
+    }
+    
+    @Override
+    public Integer call() throws Exception {
+        counter.incrementCounter();
+        return counter.getCounter();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/callables/MessageServiceCallable.java

@@ -0,0 +1,19 @@
+package com.baeldung.concurrent.threadsafety.callables;
+
+import com.baeldung.concurrent.threadsafety.services.MessageService;
+import java.util.concurrent.Callable;
+
+public class MessageServiceCallable implements Callable<String> {
+    
+    private final MessageService messageService;
+    
+    public MessageServiceCallable(MessageService messageService) {
+        this.messageService = messageService;
+    
+    }
+    
+    @Override
+    public String call() {
+        return messageService.getMesssage();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/callables/ReentranReadWriteLockCounterCallable.java

@@ -0,0 +1,20 @@
+package com.baeldung.concurrent.threadsafety.callables;
+
+import com.baeldung.concurrent.threadsafety.services.ReentrantReadWriteLockCounter;
+import java.util.concurrent.Callable;
+
+public class ReentranReadWriteLockCounterCallable implements Callable<Integer> {
+
+    private final ReentrantReadWriteLockCounter counter;
+
+    public ReentranReadWriteLockCounterCallable(ReentrantReadWriteLockCounter counter) {
+        this.counter = counter;
+    }
+    
+    @Override
+    public Integer call() throws Exception {
+        counter.incrementCounter();
+        return counter.getCounter();
+    }
+
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/callables/ReentrantLockCounterCallable.java

@@ -0,0 +1,19 @@
+package com.baeldung.concurrent.threadsafety.callables;
+
+import com.baeldung.concurrent.threadsafety.services.ReentrantLockCounter;
+import java.util.concurrent.Callable;
+
+public class ReentrantLockCounterCallable implements Callable<Integer> {
+
+    private final ReentrantLockCounter counter;
+    
+    public ReentrantLockCounterCallable(ReentrantLockCounter counter) {
+        this.counter = counter;
+    }
+    
+    @Override
+    public Integer call() throws Exception {
+        counter.incrementCounter();
+        return counter.getCounter();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/mathutils/MathUtils.java

@@ -0,0 +1,14 @@
+package com.baeldung.concurrent.threadsafety.mathutils;
+
+import java.math.BigInteger;
+
+public class MathUtils {
+    
+    public static BigInteger factorial(int number) {
+        BigInteger f = new BigInteger("1");
+        for (int i = 2; i <= number; i++) {
+            f = f.multiply(BigInteger.valueOf(i));
+        }
+        return f;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/services/AtomicCounter.java

@@ -0,0 +1,18 @@
+package com.baeldung.concurrent.threadsafety.services;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+public class AtomicCounter {
+    
+    private final AtomicInteger counter = new AtomicInteger();
+    
+    public AtomicCounter() {}
+    
+    public void incrementCounter() {
+        counter.incrementAndGet();
+    }
+    
+    public synchronized int getCounter() {
+        return counter.get();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/services/Counter.java

@@ -0,0 +1,18 @@
+package com.baeldung.concurrent.threadsafety.services;
+
+public class Counter {
+    
+    private volatile int counter;
+    
+    public Counter() {
+        this.counter = 0;
+    }
+    
+    public synchronized void incrementCounter() {
+        counter += 1;
+    }
+    
+    public int getCounter() {
+        return counter;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/services/ExtrinsicLockCounter.java

@@ -0,0 +1,23 @@
+package com.baeldung.concurrent.threadsafety.services;
+
+public class ExtrinsicLockCounter {
+
+    private int counter;
+    private final Object lock = new Object();
+
+    public ExtrinsicLockCounter() {
+        this.counter = 0;
+    }
+
+    public void incrementCounter() {
+        synchronized (lock) {
+            counter += 1;
+        }
+    }
+
+    public int getCounter() {
+        synchronized (lock) {
+            return counter;
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/services/MessageService.java

@@ -0,0 +1,14 @@
+package com.baeldung.concurrent.threadsafety.services;
+
+public class MessageService {
+    
+    private final String message;
+    
+    public MessageService(String message) {
+        this.message = message;
+    }
+    
+    public String getMesssage() {
+        return message;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/services/ReentrantLockCounter.java

@@ -0,0 +1,26 @@
+package com.baeldung.concurrent.threadsafety.services;
+
+import java.util.concurrent.locks.ReentrantLock;
+
+public class ReentrantLockCounter {
+
+    private int counter;
+    private final ReentrantLock reLock = new ReentrantLock(true);
+
+    public ReentrantLockCounter() {
+        this.counter = 0;
+    }
+
+    public void incrementCounter() {
+        reLock.lock();
+        try {
+            counter += 1;
+        } finally {
+            reLock.unlock();
+        }
+    }
+
+    public int getCounter() {
+        return counter;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/services/ReentrantReadWriteLockCounter.java

@@ -0,0 +1,34 @@
+package com.baeldung.concurrent.threadsafety.services;
+
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+public class ReentrantReadWriteLockCounter {
+    
+    private int counter;
+    private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
+    private final Lock readLock = rwLock.readLock();
+    private final Lock writeLock = rwLock.writeLock();
+    
+    public ReentrantReadWriteLockCounter() {
+        this.counter = 0;
+    }
+    
+    public void incrementCounter() {
+        writeLock.lock();
+        try {
+            counter += 1;
+        } finally {
+            writeLock.unlock();
+        }
+    }
+    
+    public int getCounter() {
+        readLock.lock();
+        try {
+            return counter;
+        } finally {
+            readLock.unlock();
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/threadsafety/services/StateHolder.java

@@ -0,0 +1,14 @@
+package com.baeldung.concurrent.threadsafety.services;
+
+public class StateHolder {
+    
+    private final String state;
+
+    public StateHolder(String state) {
+        this.state = state;
+    }
+    
+    public String getState() {
+        return state;
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/waitandnotify/Data.java

@@ -0,0 +1,39 @@
+package com.baeldung.concurrent.waitandnotify;
+
+public class Data {
+    private String packet;
+    
+    // True if receiver should wait
+    // False if sender should wait
+    private boolean transfer = true;
+ 
+    public synchronized String receive() {
+        while (transfer) {
+            try {
+                wait();
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); 
+                System.out.println("Thread Interrupted");
+            }
+        }
+        transfer = true;
+
+        notifyAll();
+        return packet;
+    }
+ 
+    public synchronized void send(String packet) {
+        while (!transfer) {
+            try { 
+                wait();
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); 
+                System.out.println("Thread Interrupted");
+            }
+        }
+        transfer = false;
+        
+        this.packet = packet;
+        notifyAll();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/waitandnotify/NetworkDriver.java

@@ -0,0 +1,12 @@
+package com.baeldung.concurrent.waitandnotify;
+
+public class NetworkDriver {
+    public static void main(String[] args) {
+        Data data = new Data();
+        Thread sender = new Thread(new Sender(data));
+        Thread receiver = new Thread(new Receiver(data));
+        
+        sender.start();
+        receiver.start();
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/waitandnotify/Receiver.java

@@ -0,0 +1,28 @@
+package com.baeldung.concurrent.waitandnotify;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+public class Receiver implements Runnable {
+    private Data load;
+ 
+    public Receiver(Data load) {
+        this.load = load;
+    }
+ 
+    public void run() {
+        for(String receivedMessage = load.receive();
+          !"End".equals(receivedMessage) ;
+          receivedMessage = load.receive()) {
+            
+            System.out.println(receivedMessage);
+
+            //Thread.sleep() to mimic heavy server-side processing
+            try {
+                Thread.sleep(ThreadLocalRandom.current().nextInt(1000, 5000));
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); 
+                System.out.println("Thread Interrupted");
+            }
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/java/com/baeldung/concurrent/waitandnotify/Sender.java

@@ -0,0 +1,33 @@
+package com.baeldung.concurrent.waitandnotify;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+public class Sender implements Runnable {
+    private Data data;
+ 
+    public Sender(Data data) {
+        this.data = data;
+    }
+ 
+    public void run() {
+        String packets[] = {
+          "First packet",
+          "Second packet",
+          "Third packet",
+          "Fourth packet",
+          "End"
+        };
+ 
+        for (String packet : packets) {
+            data.send(packet);
+            
+            //Thread.sleep() to mimic heavy server-side processing
+            try {
+                Thread.sleep(ThreadLocalRandom.current().nextInt(1000, 5000));
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt(); 
+                System.out.println("Thread Interrupted");
+            }
+        }
+    }
+}

core-java-modules/core-java-concurrency-basic/src/main/resources/logback.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <logger name="org.springframework" level="WARN" />
+    <logger name="org.springframework.transaction" level="WARN" />
+
+    <!-- in order to debug some marshalling issues, this needs to be TRACE -->
+    <logger name="org.springframework.web.servlet.mvc" level="WARN" />
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>