Add example of joining threads

Author: abhinav-nath

README.md

@@ -6,13 +6,14 @@ Simple and easy to understand code examples for most of the Concurrent APIs prov
 #### All about Threads
 - [Motivation - Why do we need Threads?](./notes/threads-motivation.md)
 - [Threads in Java](./src/com/codecafe/concurrency/thread)
-  - [Creating Threads](./notes/creating-threads.md) using
+  - [Creating Threads](./notes/creating-threads.md) using:
     - [Runnable](./src/com/codecafe/concurrency/thread/basics/designathread/ThreadDemo.java)
     - [Thread class](./src/com/codecafe/concurrency/thread/basics/designathread/ThreadDemo.java)
     - [Callable](./src/com/codecafe/concurrency/thread/basics/designathread/CallableDemo.java)
     - [ExecutorService](notes/executorservice.md) - [[code](./src/com/codecafe/concurrency/executorservice/ExecutorServiceDemo.java)]
   - [Thread States](./notes/thread-states.md) - [[code](./src/com/codecafe/concurrency/thread/basics/designathread/ThreadStates.java)]
   - [Thread Termination](./src/com/codecafe/concurrency/thread/basics/Main.java)
+  - [Joining Threads](./src/com/codecafe/concurrency/thread/joiningthreads/Main.java)
 - [Thread Signalling](./src/com/codecafe/concurrency/threadsignalling)
 - [Daemon Threads](./notes/daemon-threads.md) - [[code](./src/com/codecafe/concurrency/thread/daemonthreads/Main.java)]
 

src/com/codecafe/concurrency/thread/joiningthreads/FactorialTask.java

@@ -0,0 +1,39 @@
+package com.codecafe.concurrency.thread.joiningthreads;
+
+import java.math.BigInteger;
+
+public class FactorialTask implements Runnable {
+
+  private final long number;
+  private BigInteger result = BigInteger.ZERO;
+  private boolean isFinished = false;
+
+  public FactorialTask(long number) {
+    this.number = number;
+  }
+
+  @Override
+  public void run() {
+    this.result = factorial(number);
+    this.isFinished = true;
+  }
+
+  public BigInteger factorial(long n) {
+    BigInteger tempResult = BigInteger.ONE;
+
+    for (long i = n; i > 0; i--) {
+      tempResult = tempResult.multiply(new BigInteger(Long.toBinaryString(i)));
+    }
+
+    return tempResult;
+  }
+
+  public boolean isFinished() {
+    return isFinished;
+  }
+
+  public BigInteger getResult() {
+    return result;
+  }
+
+}

src/com/codecafe/concurrency/thread/joiningthreads/Main.java

@@ -0,0 +1,41 @@
+package com.codecafe.concurrency.thread.joiningthreads;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Main {
+
+  public static void main(String[] args) throws InterruptedException {
+    List<Long> numbers = List.of(0L, 5653L, 9090L, 30467L, 27L, 2276L);
+
+    List<FactorialTask> factorialTasks = new ArrayList<>();
+    List<Thread> factorialThreads = new ArrayList<>();
+
+    for (long number : numbers) {
+      factorialTasks.add(new FactorialTask(number));
+    }
+
+    for (FactorialTask factorialTask : factorialTasks) {
+      factorialThreads.add(new Thread(factorialTask));
+    }
+
+    for (Thread th : factorialThreads) {
+      th.start();
+    }
+
+    for (Thread th : factorialThreads) {
+      th.join(2000);
+    }
+
+    for (int i = 0; i < numbers.size(); i++) {
+      FactorialTask factorialTask = factorialTasks.get(i);
+
+      if (factorialTask.isFinished()) {
+        System.out.println("Factorial of " + numbers.get(i) + " is " + factorialTask.getResult());
+      } else {
+        System.out.println("The calculation for " + numbers.get(i) + " is still in progress");
+      }
+    }
+  }
+
+}