diff --git a/src/exercises/ex_o/LockedWithConditionsStack.java b/src/exercises/ex_o/LockedWithConditionsStack.java
new file mode 100644
index 0000000..e14d797
--- /dev/null
+++ b/src/exercises/ex_o/LockedWithConditionsStack.java
@@ -0,0 +1,51 @@
+package exercises.ex_o;
+
+import java.util.Stack;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class LockedWithConditionsStack {
+    private final int capacity;
+    private final Stack<Integer> stack = new Stack<>();
+    private final ReentrantLock lock = new ReentrantLock();
+    private final Condition fullCondition = lock.newCondition();
+    private final Condition emptyCondition = lock.newCondition();
+
+    public LockedWithConditionsStack(int capacity) {
+        this.capacity = capacity;
+    }
+
+    public void pushToStack(int value) {
+        try {
+            lock.lock();
+            while (stack.size() == capacity) {
+                System.out.println("Stack is full, waiting until someone pops");
+                fullCondition.await();
+            }
+            stack.push(value);
+            emptyCondition.signalAll();
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        } finally {
+            lock.unlock();
+        }
+    }
+
+    public int popFromStack() {
+        int value;
+        try {
+            lock.lock();
+            while (stack.isEmpty()) {
+                System.out.println("Stack is empty, waiting until someone pushes");
+                emptyCondition.await();
+            }
+            value = stack.pop();
+            fullCondition.signalAll();
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        } finally {
+            lock.unlock();
+        }
+        return value;
+    }
+}
diff --git a/src/exercises/ex_o/NumberConsumer.java b/src/exercises/ex_o/NumberConsumer.java
new file mode 100644
index 0000000..6643f01
--- /dev/null
+++ b/src/exercises/ex_o/NumberConsumer.java
@@ -0,0 +1,16 @@
+package exercises.ex_o;
+
+public class NumberConsumer implements Runnable {
+    private LockedWithConditionsStack stack;
+
+    public NumberConsumer(LockedWithConditionsStack stack) {
+        this.stack = stack;
+    }
+
+    @Override
+    public void run() {
+        while (true) {
+            System.out.println("Pop from stack: " + stack.popFromStack());
+        }
+    }
+}
diff --git a/src/exercises/ex_o/NumberProducer.java b/src/exercises/ex_o/NumberProducer.java
new file mode 100644
index 0000000..112cfa4
--- /dev/null
+++ b/src/exercises/ex_o/NumberProducer.java
@@ -0,0 +1,17 @@
+package exercises.ex_o;
+
+public class NumberProducer implements Runnable {
+    private LockedWithConditionsStack stack;
+    public NumberProducer(LockedWithConditionsStack stack) {
+        this.stack = stack;
+    }
+
+    @Override
+    public void run() {
+        for (int i = 0; i < 100; i++) {
+            System.out.println("Pushing to stack " + i + "...");
+            stack.pushToStack(i);
+            System.out.println("Pushed to stack " + i);
+        }
+    }
+}
diff --git a/src/exercises/ex_o/TestingReentrantLockWithConditions.java b/src/exercises/ex_o/TestingReentrantLockWithConditions.java
new file mode 100644
index 0000000..62883bc
--- /dev/null
+++ b/src/exercises/ex_o/TestingReentrantLockWithConditions.java
@@ -0,0 +1,9 @@
+package exercises.ex_o;
+
+public class TestingReentrantLockWithConditions {
+    public static void main(String[] args) {
+        LockedWithConditionsStack stack = new LockedWithConditionsStack(5);
+        (new Thread(new NumberProducer(stack))).start();
+        (new Thread(new NumberConsumer(stack))).start();
+    }
+}