pp.A4-HandOverHandLocking/src/main/java/pp/Main.java

@@ -1,6 +1,5 @@
 package pp;
 
-
 public class Main {
     static SimplifiedList<Integer> list;
 

pp.A4-HandOverHandLocking/src/main/java/pp/ThreadsafeSimplifiedList.java

@@ -1,15 +1,19 @@
 package pp;
 
+import lombok.Synchronized;
+import net.jcip.annotations.ThreadSafe;
+
+@ThreadSafe
 public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
   private Node<T> first;
 
-  private static class Node<U> {
+  private class Node<U> {
-    U element;
+    private U element;
-    Node<U> prev;
+    private Node<U> prev;
-    Node<U> next;
+    private Node<U> next;
-    final Object lock = new Object();
 
-    Node(U element, Node<U> prev, Node<U> next) {
+    private Node(U element, Node<U> prev, Node<U> next) {
+      super();
       this.element = element;
       this.prev = prev;
       this.next = next;
@@ -17,84 +21,78 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
   }
 
   public ThreadsafeSimplifiedList() {
+    super();
     this.first = null;
   }
 
+  /**
+   * Returns the element at the specified position in this list.
+   *
+   * @param index index of the element to return
+   * @return the element at the specified position in this list
+   */
   @Override
-  public boolean add(T element) {
+  @Synchronized
-    synchronized (this) {
-      if (first == null) {
-        first = new Node<>(element, null, null);
-        return true;
-      }
-    }
-
-    Node<T> curr;
-    synchronized (first.lock) {
-      curr = first;
-      while (true) {
-        Node<T> next;
-        synchronized (curr.lock) {
-          next = curr.next;
-          if (next == null) {
-            // letztes Element erreicht → neues anhängen
-            curr.next = new Node<>(element, curr, null);
-            return true;
-          }
-        }
-        synchronized (next.lock) {
-          curr = next;
-        }
-      }
-    }
-  }
-
-  @Override
   public T get(int index) {
-    Node<T> curr;
+    var ptr = this.first;
-    synchronized (this) {
+    for (var j = 0; j < index; j++) {
-      if (first == null) throw new IndexOutOfBoundsException();
+      ptr = ptr.next;
-      curr = first;
-    }
-
-    synchronized (curr.lock) {
-      for (int i = 0; i < index; i++) {
-        Node<T> next = curr.next;
-        if (next == null) throw new IndexOutOfBoundsException();
-        synchronized (next.lock) {
-          curr = next;
-        }
-      }
-      return delay(curr.element);
     }
+    return delay(ptr.element);
   }
 
+  /**
+   * Appends the specified element to the end of this list. There are no
+   * limitations on what elements may be added to this list.
+   * 
+   * @param element element to be appended to this list
+   * @return true
+   * @see java.util.Collection#add(Object)
+   *
+   */
   @Override
+  @Synchronized
+  public boolean add(T element) {
+    if (this.first != null) {
+      var ptr = this.first;
+      while (ptr.next != null) {
+        ptr = ptr.next;
+      }
+      ptr.next = new Node<>(element, ptr, null);
+    } else {
+      this.first = new Node<>(element, null, null);
+    }
+    return true;
+  }
+
+  /**
+   * Replaces the element at the specified position in this list with the
+   * specified element.
+   * 
+   * @param index   index of the element to replace
+   * @param element element to be stored at the specified position
+   * @return the element previously at the specified position
+   */
+  @Override
+  @Synchronized
   public T set(int index, T element) {
-    Node<T> curr;
+    var ptr = this.first;
-    synchronized (this) {
+    for (var j = 0; j < index; j++) {
-      if (first == null) throw new IndexOutOfBoundsException();
+      ptr = ptr.next;
-      curr = first;
-    }
-
-    synchronized (curr.lock) {
-      for (int i = 0; i < index; i++) {
-        Node<T> next = curr.next;
-        if (next == null) throw new IndexOutOfBoundsException();
-        synchronized (next.lock) {
-          curr = next;
-        }
-      }
-      T old = curr.element;
-      curr.element = element;
-      return old;
     }
+    var prevElement = ptr.element;
+    ptr.element = element;
+    return prevElement;
   }
 
+  /**
+   * Returns true if this list contains no elements.
+   * 
+   * @return true if this list contains no elements
+   */
   @Override
+  @Synchronized
   public boolean isEmpty() {
-    synchronized (this) {
+    return this.first == null;
-      return first == null;
-    }
   }
 }