JUnit tests

mutex/src/main/java/com/iluwatar/mutex/App.java

@@ -40,7 +40,7 @@ public class App {
    */
   public static void main(String[] args) {
     Mutex mutex = new Mutex();
-    Jar jar = new Jar(mutex);
+    Jar jar = new Jar(1000, mutex);
     Thief peter = new Thief("Peter", jar);
     Thief john = new Thief("John", jar);
     peter.start();

mutex/src/main/java/com/iluwatar/mutex/Jar.java

@@ -37,16 +37,17 @@ public class Jar {
   /**
    * The resource within the jar.
    */
-  private int beans = 1000;
+  private int beans;
 
-  public Jar(Lock lock) {
+  public Jar(int beans, Lock lock) {
+    this.beans = beans;
     this.lock = lock;
   }
 
   /**
    * Method for a thief to take a bean.
    */
-  public boolean takeBean(Thief thief) {
+  public boolean takeBean() {
     boolean success = false;
     try {
       lock.acquire();

mutex/src/main/java/com/iluwatar/mutex/Mutex.java

@@ -32,6 +32,13 @@ public class Mutex implements Lock {
    */
   private Object owner;
 
+  /**
+   * Returns the current owner of the Mutex, or null if available
+   */
+  public Object getOwner() {
+    return owner;
+  }
+  
   /**
    * Method called by a thread to acquire the lock. If the lock has already
    * been acquired this will wait until the lock has been released to 
@@ -51,8 +58,10 @@ public class Mutex implements Lock {
    */
   @Override
   public synchronized void release() {
-    owner = null;
-    notify();
+    if (Thread.currentThread() == owner) {
+      owner = null;
+      notify();
+    }
   }
 
 }

mutex/src/main/java/com/iluwatar/mutex/Thief.java

@@ -51,7 +51,7 @@ public class Thief extends Thread {
   public void run() {
     int beans = 0;
 
-    while (jar.takeBean(this)) {
+    while (jar.takeBean()) {
       beans = beans + 1;
       System.out.println(name + " took a bean.");
     }