added ex D

src/exercicses/ex_d/EmptyingThread.java

@@ -0,0 +1,23 @@
+package exercicses.ex_d;
+
+import java.util.Stack;
+
+public class EmptyingThread extends Thread {
+    private Stack<Integer> source;
+    private Stack<Integer> target;
+
+    public EmptyingThread(Stack<Integer> source, Stack<Integer> target) {
+        this.source = source;
+        this.target = target;
+    }
+
+    @Override
+    public void run() {
+        int v;
+        while (!source.isEmpty()) {
+            v = source.pop();
+            System.out.println("Number popped from source stack and pushed to target stack: " + v);
+            target.push(v);
+        }
+    }
+}

src/exercicses/ex_d/FillingThread.java

@@ -0,0 +1,31 @@
+package exercicses.ex_d;
+
+import java.util.Stack;
+
+public class FillingThread extends Thread {
+    private Stack<Integer> source;
+    private Stack<Integer> target;
+    private Thread emptyingThread;
+
+    public FillingThread(Stack<Integer> source, Stack<Integer> target, Thread emptyingThread) {
+        this.source = source;
+        this.target = target;
+        this.emptyingThread = emptyingThread;
+    }
+
+    @Override
+    public void run() {
+        try {
+            emptyingThread.join();
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        }
+        System.out.println("--- Starting Filling back ---");
+        int v;
+        while (!target.isEmpty()) {
+            v = target.pop();
+            System.out.println("From target stack to source stack " + v);
+            source.push(v);
+        }
+    }
+}

src/exercicses/ex_d/TestingJoins.java

@@ -0,0 +1,18 @@
+package exercicses.ex_d;
+
+import java.util.Stack;
+
+public class TestingJoins {
+    public static void main(String[] args) {
+        Stack<Integer> sourceStack = new Stack<Integer>();
+        Stack<Integer> targetStack = new Stack<Integer>();
+        // Populating the first sourceStack
+        for (int i = 1; i <= 10; i++) {
+            sourceStack.push(i);
+        }
+        Thread emptyingThread = new EmptyingThread(sourceStack, targetStack);
+        Thread fillingThread = new FillingThread(sourceStack, targetStack, emptyingThread);
+        emptyingThread.start();
+        fillingThread.start();
+    }
+}