added ex R

src/exercises/ex_r/Customer.java

@@ -0,0 +1,28 @@
+package exercises.ex_r;
+
+public class Customer implements Runnable {
+    private String name;
+    private PostOffice office;
+
+    public Customer(String name, PostOffice office) {
+        this.name = name;
+        this.office = office;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public void run() {
+        while (true) {
+            Package pkg = new Package(this);
+            office.registerPackage(pkg);
+            try {
+                Thread.sleep((long) (1000L + 5000L * Math.random()));
+            } catch (InterruptedException e) {
+                break;
+            }
+        }
+    }
+}

src/exercises/ex_r/Package.java

@@ -0,0 +1,15 @@
+package exercises.ex_r;
+
+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_r/PostOffice.java

@@ -0,0 +1,19 @@
+package exercises.ex_r;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+
+public class PostOffice {
+    private BlockingQueue<Package> packages = new LinkedBlockingQueue<>();
+
+    public void registerPackage(Package pkg) {
+        packages.add(pkg);
+        System.out.println("Registered " + pkg + " (now " + packages.size() + ")");
+    }
+
+    public Package takePackage() throws InterruptedException {
+        Package pkg = packages.take();
+        System.out.println("Withdrawn " + pkg + " (now " + packages.size() + ")");
+        return pkg;
+    }
+}

src/exercises/ex_r/Postman.java

@@ -0,0 +1,22 @@
+package exercises.ex_r;
+
+public class Postman implements Runnable {
+    private PostOffice office;
+
+    public Postman(PostOffice office) {
+        this.office = office;
+    }
+
+    @Override
+    public void run() {
+        while (true) {
+            try {
+                Package pkg = office.takePackage();
+                Thread.sleep((long) (1000L + 2000L * Math.random()));
+                System.out.println("Delivered " + pkg);
+            } catch (InterruptedException e) {
+                break;
+            }
+        }
+    }
+}

src/exercises/ex_r/TestingBlockingQueue_PostOffice.java

@@ -0,0 +1,10 @@
+package exercises.ex_r;
+
+public class TestingBlockingQueue_PostOffice {
+    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();
+    }
+}