some changes from practice group

VL14/Aufgabe02/Aufgabe02.java

@@ -8,23 +8,21 @@ import java.util.Random;
  * @author Sebastian Brosch
  */
 public class Aufgabe02 {
-  public static void main(String[] args) {
-    final int NUMBER_OF_USERS = 10;
+  public static void main(String[] args) throws Exception {
+    final int NUMBER_OF_USERS = 2;
     final int NUMBER_OF_PRINTERS = 2;
 
-    // create some users.
-    for (int u = 0; u < NUMBER_OF_USERS; u++) {
-      User user = new User(getRandomNumber(1, 10) * 1000);
-      Thread threadUser = new Thread(user);
-      threadUser.start();
-    }
-
     // create some printers.
     for (int p = 0; p < NUMBER_OF_PRINTERS; p++) {
-      Printer printer = new Printer();
-      Thread threadPrinter = new Thread(printer);
+      Thread threadPrinter = new Thread(new Printer());
       threadPrinter.start();
     }
+
+    // create some users.
+    for (int u = 0; u < NUMBER_OF_USERS; u++) {
+      Thread threadUser = new Thread(new User(getRandomNumber(1, 10) * 1000));
+      threadUser.start();
+    }
   }
 
   /**

VL14/Aufgabe02/Printer.java

@@ -10,12 +10,8 @@ public class Printer implements Runnable {
     while (true) {
       synchronized (PrinterQueue.queue) {
         if (PrinterQueue.queue.size() > 0) {
-          System.out.println("Printer " + Thread.currentThread().threadId() + " prints: " + PrinterQueue.queue.poll());
-        } else {
-          try {
-            PrinterQueue.queue.wait();
-          } catch (InterruptedException e) {
-          }
+          System.out.println("Printer " + Thread.currentThread().threadId() + " prints: " + PrinterQueue.queue.getFirst());
+          PrinterQueue.queue.removeFirst();
         }
       }
     }

VL14/Aufgabe02/PrinterQueue.java

@@ -1,6 +1,8 @@
 package VL14.Aufgabe02;
 
-import java.util.LinkedList;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 /**
  * Class which represents a printer queue.
@@ -8,5 +10,5 @@ import java.util.LinkedList;
  * @author Sebastian Brosch
  */
 public class PrinterQueue {
-  static LinkedList<Integer> queue = new LinkedList<Integer>();
+  static List<Object> queue = Collections.synchronizedList(new ArrayList<>());
 }

VL14/Aufgabe02/User.java

@@ -7,7 +7,7 @@ package VL14.Aufgabe02;
  */
 public class User implements Runnable {
   private int number = 0;
-  private int wait = 0;
+  private long wait = 0;
 
   /**
    * Constructor to initialize a User.
@@ -26,18 +26,11 @@ public class User implements Runnable {
   }
 
   public void run() {
-    while (true) {
-      synchronized (PrinterQueue.queue) {
-        int data = this.number++;
-        PrinterQueue.queue.add(data);
-        System.out.println("User " + Thread.currentThread().threadId() + " adds: " + data);
-        PrinterQueue.queue.notifyAll();
-      }
-
-      try {
-        Thread.sleep(this.wait);
-      } catch (InterruptedException e) {
-      }
+    while (this.wait > 0) {
+      int data = this.number++;
+      PrinterQueue.queue.add(data);
+      System.out.println("User " + Thread.currentThread().threadId() + " added " + data);
+      this.wait--;
     }
   }
 }