corejava第10版

corejava第10版/v1ch09/circularArrayQueue/CircularArrayQueueTest.java

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+package circularArrayQueue;
+
+import java.util.*;
+
+/**
+ * This program demonstrates how to extend the collections framework.
+ * @version 1.21 2012-01-26
+ * @author Cay Horstmann
+ */
+public class CircularArrayQueueTest
+{
+   public static void main(String[] args)
+   {
+      Queue<String> q = new CircularArrayQueue<>(5);
+      q.add("Amy");
+      q.add("Bob");
+      q.add("Carl");
+      q.add("Deedee");
+      q.add("Emile");
+      q.remove();
+      q.add("Fifi");
+      q.remove();
+      for (String s : q) System.out.println(s);
+   }
+}
+
+/** 
+    A first-in, first-out bounded collection. 
+*/ 
+class CircularArrayQueue<E> extends AbstractQueue<E>
+{ 
+   private Object[] elements; 
+   private int head; 
+   private int tail; 
+   private int count; 
+   private int modcount;
+
+   /** 
+       Constructs an empty queue. 
+       @param capacity the maximum capacity of the queue 
+   */ 
+   public CircularArrayQueue(int capacity) 
+   { 
+      elements = new Object[capacity]; 
+      count = 0; 
+      head = 0; 
+      tail = 0; 
+   } 
+
+   public boolean offer(E newElement) 
+   { 
+      assert newElement != null;
+      if (count < elements.length) 
+      {
+         elements[tail] = newElement; 
+         tail = (tail + 1) % elements.length; 
+         count++;
+         modcount++;
+         return true;
+      }
+      else 
+         return false;
+   } 
+
+   public E poll() 
+   { 
+      if (count == 0) return null;
+      E r = peek(); 
+      head = (head + 1) % elements.length; 
+      count--; 
+      modcount++;
+      return r; 
+   } 
+
+   @SuppressWarnings("unchecked")
+   public E peek() 
+   { 
+      if (count == 0) return null;
+      return (E) elements[head]; 
+   } 
+
+   public int size() 
+   { 
+      return count; 
+   } 
+
+   public Iterator<E> iterator()
+   {
+      return new QueueIterator();
+         
+   }
+
+   private class QueueIterator implements Iterator<E>
+   {
+      private int offset;
+      private int modcountAtConstruction;
+
+      public QueueIterator()
+      {
+         modcountAtConstruction = modcount;
+      }
+
+      @SuppressWarnings("unchecked")
+      public E next() 
+      { 
+         if (!hasNext()) throw new NoSuchElementException();
+         E r = (E) elements[(head + offset) % elements.length]; 
+         offset++;
+         return r;
+      }
+
+      public boolean hasNext() 
+      { 
+         if (modcount != modcountAtConstruction) 
+            throw new ConcurrentModificationException();
+         return offset < count;
+      }
+
+      public void remove() 
+      { 
+         throw new UnsupportedOperationException(); 
+      }
+   }
+}