Added Thread Join example simulating complex calculations done through multiple threads and then main thread waits other threads to finish their work then aggregates the results.

Author: ahmedrafat-SW

src/main/java/com/dev/thread/ComplexCalculationThreadJoin.java

@@ -0,0 +1,65 @@
+package com.dev.thread;
+
+import java.math.BigInteger;
+
+public class ComplexCalculationThreadJoin {
+    public BigInteger calculateResult(BigInteger base1, BigInteger power1, BigInteger base2, BigInteger power2) {
+        BigInteger result;
+        /*
+            Calculate result = ( base1 ^ power1 ) + (base2 ^ power2).
+            Where each calculation in (..) is calculated on a different thread
+        */
+        PowerCalculatingThread thread1 = new PowerCalculatingThread(base1, power1);
+        PowerCalculatingThread thread2 = new PowerCalculatingThread(base2, power2);
+
+        thread1.start();
+        thread2.start();
+
+        try {
+            thread1.join(); // Wait for thread1 to complete
+            thread2.join(); // Wait for thread2 to complete
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            return BigInteger.ZERO; // Or handle error appropriately
+        }
+
+        result = thread1.getResult().add(thread2.getResult());
+
+        return result;
+    }
+
+    private static class PowerCalculatingThread extends Thread {
+        private BigInteger result = BigInteger.ZERO; // Changed default from ONE to ZERO
+        private final BigInteger base;    // Made final
+        private final BigInteger power;   // Made final
+
+        public PowerCalculatingThread(BigInteger base, BigInteger power) {
+            this.base = base;
+            this.power = power;
+        }
+
+        @Override
+        public void run() {
+            /*
+            Implement the calculation of result = base ^ power
+            */
+            result = base.pow(power.intValueExact()); // Changed from Math.pow to BigInteger.pow
+        }
+
+        public BigInteger getResult() {
+            return result;
+        }
+    }
+
+    // For testing
+    public static void main(String[] args) {
+        ComplexCalculationThreadJoin calc = new ComplexCalculationThreadJoin();
+        BigInteger result = calc.calculateResult(
+                BigInteger.valueOf(100),
+                BigInteger.valueOf(30),
+                BigInteger.valueOf(30),
+                BigInteger.valueOf(209)
+        );
+        System.out.println(result); // Should print 17 (2³ + 3² = 8 + 9 = 17)
+    }
+}