add deadlock example

Author: joney000

Concurrency/Deadlock.java

@@ -0,0 +1,42 @@
+// ref: 
+// https://docs.oracle.com/javase/tutorial/essential/concurrency/sync.html
+// https://docs.oracle.com/javase/tutorial/essential/concurrency/deadlock.html
+
+public class Deadlock {
+    static class Friend {
+        private final String name;
+        
+        public Friend(String name) {
+            this.name = name;
+        }
+
+        public String getName() {
+            return this.name;
+        }
+
+        public synchronized void bow(Friend bower) {
+            System.out.format("%s: %s"
+                + "  has bowed to me!%n", 
+                this.name, bower.getName());
+            bower.bowBack(this);
+        }
+
+        public synchronized void bowBack(Friend bower) {
+            System.out.format("%s: %s"
+                + " has bowed back to me!%n",
+                this.name, bower.getName());
+        }
+    }
+
+    public static void main(String[] args) throws Exception{
+        final Friend alphonse = new Friend("Alphonse");
+        final Friend gaston = new Friend("Gaston");
+        new Thread(new Runnable() {
+            public void run() { alphonse.bow(gaston); }
+        }).start();
+        // Thread.sleep(10000);
+        new Thread(new Runnable() {
+            public void run() { gaston.bow(alphonse); }
+        }).start();
+    }
+}