now using wait and notify

VL14/Aufgabe02/Aufgabe02.java

@@ -1,5 +1,7 @@
 package VL14.Aufgabe02;
 
+import java.util.Random;
+
 /**
  * Vorlesung 14 / Aufgabe 2
  *
@@ -7,12 +9,12 @@ package VL14.Aufgabe02;
  */
 public class Aufgabe02 {
   public static void main(String[] args) {
-    final int NUMBER_OF_USERS = 5;
+    final int NUMBER_OF_USERS = 10;
     final int NUMBER_OF_PRINTERS = 2;
 
     // create some users.
     for (int u = 0; u < NUMBER_OF_USERS; u++) {
-      User user = new User();
+      User user = new User(getRandomNumber(1, 10) * 1000);
       Thread threadUser = new Thread(user);
       threadUser.start();
     }
@@ -24,4 +26,15 @@ public class Aufgabe02 {
       threadPrinter.start();
     }
   }
+
+  /**
+   * Method to determine a random number from a certain range.
+   *
+   * @param start The first number of the range.
+   * @param end   The last number of the range.
+   * @return A random number from a certain range.
+   */
+  private static int getRandomNumber(int start, int end) {
+    return (new Random()).nextInt((end - start + 1)) + start;
+  }
 }

VL14/Aufgabe02/Printer.java

@@ -10,14 +10,14 @@ public class Printer implements Runnable {
     while (true) {
       synchronized (PrinterQueue.queue) {
         if (PrinterQueue.queue.size() > 0) {
-          System.out.println(PrinterQueue.queue.poll());
+          System.out.println("Printer " + Thread.currentThread().threadId() + " prints: " + PrinterQueue.queue.poll());
+        } else {
+          try {
+            PrinterQueue.queue.wait();
+          } catch (InterruptedException e) {
+          }
         }
       }
-
-      try {
-        Thread.sleep(500);
-      } catch (InterruptedException e) {
-      }
     }
   }
 }

VL14/Aufgabe02/PrinterQueue.java

@@ -8,5 +8,5 @@ import java.util.LinkedList;
  * @author Sebastian Brosch
  */
 public class PrinterQueue {
-  static LinkedList<String> queue = new LinkedList<String>();
+  static LinkedList<Integer> queue = new LinkedList<Integer>();
 }

VL14/Aufgabe02/User.java

@@ -7,15 +7,35 @@ package VL14.Aufgabe02;
  */
 public class User implements Runnable {
   private int number = 0;
+  private int wait = 0;
+
+  /**
+   * Constructor to initialize a User.
+   */
+  public User() {
+    this.wait = 1000;
+  }
+
+  /**
+   * Constructor to initialize a User.
+   *
+   * @param wait The time the user is waiting for creating new print jobs.
+   */
+  public User(int wait) {
+    this.wait = wait;
+  }
 
   public void run() {
     while (true) {
       synchronized (PrinterQueue.queue) {
-        PrinterQueue.queue.add(Thread.currentThread().getName() + ": " + this.number++);
+        int data = this.number++;
+        PrinterQueue.queue.add(data);
+        System.out.println("User " + Thread.currentThread().threadId() + " adds: " + data);
+        PrinterQueue.queue.notifyAll();
       }
 
       try {
-        Thread.sleep(100);
+        Thread.sleep(this.wait);
       } catch (InterruptedException e) {
       }
     }