added ex K

src/exercises/ex_k/Customer.java

@@ -0,0 +1,31 @@
+package exercises.ex_k;
+
+public class Customer implements Runnable {
+    private String name;
+    private PostOffice postOffice;
+
+    public Customer(String name, PostOffice postOffice) {
+        this.name = name;
+        this.postOffice = postOffice;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public void run() {
+        Package pkg;
+        while (true) {
+            pkg = new Package(this);
+            System.out.println("Registering " + pkg + "...");
+            postOffice.registerPackage(pkg);
+            System.out.println("Registered " + pkg);
+            try {
+                Thread.sleep((long) (Math.random() * 2000 + 1000));
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+}

src/exercises/ex_k/Package.java

@@ -0,0 +1,15 @@
+package exercises.ex_k;
+
+public class Package {
+    private Customer sender;
+
+    public Package(Customer sender) {
+        this.sender = sender;
+    }
+    @Override
+    public String toString() {
+        return "Package{" +
+            "sender=" + sender.getName() +
+            '}';
+    }
+}

src/exercises/ex_k/PostOffice.java

@@ -0,0 +1,38 @@
+package exercises.ex_k;
+
+import java.util.LinkedList;
+import java.util.List;
+
+public class PostOffice {
+    public static final int CAPACITY = 5;
+    private List<Package> packages = new LinkedList<>();
+
+    public synchronized void registerPackage(Package pkg) {
+        while (packages.size() >= CAPACITY) {
+            try {
+                System.out.println("[PostOffice] Storage is full, waiting");
+                wait();
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+        }
+        packages.add(pkg);
+        System.out.println("[PostOffice] Storage: " + packages.size() + " / " + CAPACITY);
+        notifyAll();
+    }
+
+    public synchronized Package getNextPackage() {
+        while (packages.isEmpty()) {
+            try {
+                System.out.println("[PostOffice] Storage is empty, waiting");
+                wait();
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+        }
+        Package pkg = packages.removeFirst();
+        System.out.println("[PostOffice] Storage: " + packages.size() + " / " + CAPACITY);
+        notifyAll();
+        return pkg;
+    }
+}

src/exercises/ex_k/Postman.java

@@ -0,0 +1,23 @@
+package exercises.ex_k;
+
+public class Postman implements Runnable {
+    private PostOffice postOffice;
+
+    public Postman(PostOffice postOffice) {
+        this.postOffice = postOffice;
+    }
+
+    @Override
+    public void run() {
+        Package pkg;
+        while (true) {
+            pkg = postOffice.getNextPackage();
+            System.out.println("Delivering " + pkg);
+            try {
+                Thread.sleep(2000);
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+        }
+    }
+}

src/exercises/ex_k/TestingGuardedBlocks.java

@@ -0,0 +1,10 @@
+package exercises.ex_k;
+
+public class TestingGuardedBlocks {
+    public static void main(String[] args) {
+        PostOffice postOffice = new PostOffice();
+        (new Thread(new Postman(postOffice))).start();
+        (new Thread(new Customer("Mrs Darbellay", postOffice))).start();
+        (new Thread(new Customer("Mrs Müller", postOffice))).start();
+    }
+}