TAO/examples/Simulator/DOVEBrowser/Queue.java

   1
   2 import java.util.Enumeration;
   3
   4 public class Queue
   5 {
   6   // Friendly?
   7   Queue_Node head_ = null;
   8   Queue_Node tail_ = null;
   9
  10   private int length_ = 0;
  11
  12   public Queue()
  13     {
  14     }
  15
  16   public Enumeration forward_iterator()
  17     {
  18       return new Queue_Iterator(this, Queue_Iterator.FORWARD);
  19     }
  20
  21   public Enumeration reverse_iterator()
  22     {
  23       return new Queue_Iterator(this, Queue_Iterator.REVERSE);
  24     }
  25
  26   public void enqueue_tail(Object new_data)
  27     {
  28       Queue_Node new_node = new Queue_Node(new_data);
  29
  30       if (tail_ == null)
  31         {
  32           tail_ = new_node;
  33           head_ = new_node;
  34         }
  35       else
  36         {
  37           new_node.prev_ = tail_;
  38           tail_.next_ = new_node;
  39           tail_ = new_node;
  40         }
  41
  42       length_++;
  43     }
  44
  45   public void enqueue_head(Object new_data)
  46     {
  47       Queue_Node new_node = new Queue_Node(new_data);
  48
  49       if (head_ == null)
  50         {
  51           tail_ = new_node;
  52           head_ = new_node;
  53         }
  54       else
  55         {
  56           new_node.next_ = head_;
  57           head_.prev_ = new_node;
  58           head_ = new_node;
  59         }
  60
  61       length_++;
  62     }
  63
  64   public Object dequeue_head()
  65     {
  66       Object return_value = null;
  67
  68       if (head_ == null)
  69         return_value = null;
  70       else if (tail_ == head_)
  71         {
  72           return_value = head_.data_;
  73           tail_ = null;
  74           head_ = null;
  75         }
  76       else
  77         {
  78           return_value = head_.data_;
  79           head_ = head_.next_;
  80           head_.prev_ = null;
  81         }
  82
  83       length_--;
  84
  85       return return_value;
  86     }
  87
  88   public Object dequeue_tail()
  89     {
  90       Object return_value = null;
  91
  92       if (tail_ == null)
  93         return_value = null;
  94       else if (tail_ == head_)
  95         {
  96           return_value = tail_.data_;
  97           tail_ = null;
  98           head_ = null;
  99         }
 100       else
 101         {
 102           return_value = tail_.data_;
 103           tail_ = tail_.prev_;
 104           tail_.next_ = null;
 105         }
 106
 107       length_--;
 108
 109       return return_value;
 110     }
 111
 112   public int length()
 113     {
 114       return length_;
 115     }
 116
 117   public Object head()
 118     {
 119       if (head_ != null)
 120         return head_.data_;
 121       else
 122         return null;
 123     }
 124
 125   public Object tail()
 126     {
 127       if (tail_ != null)
 128         return tail_.data_;
 129       else
 130         return null;
 131     }
 132 }
 133
 134 class Queue_Node
 135 {
 136   public Queue_Node prev_ = null;
 137   public Queue_Node next_ = null;
 138   public Object data_;
 139
 140   public Queue_Node(Object data)
 141     {
 142       data_ = data;
 143     }
 144 }
 145
 146 class Queue_Iterator implements Enumeration
 147 {
 148   public static final boolean FORWARD = true;
 149   public static final boolean REVERSE = false;
 150
 151   private Queue queue_;
 152   private Queue_Node queue_ptr_;
 153   private boolean direction_ = FORWARD;
 154
 155   public Queue_Iterator(Queue queue)
 156     {
 157       queue_ = queue;
 158       queue_ptr_ = queue.head_;
 159     }
 160
 161   public Queue_Iterator(Queue queue, boolean direction)
 162     {
 163       queue_ = queue;
 164       direction_ = direction;
 165
 166       if (direction_)
 167         queue_ptr_ = queue_.head_;
 168       else
 169         queue_ptr_ = queue_.tail_;
 170     }
 171
 172   public Object nextElement()
 173     {
 174       Object data = queue_ptr_.data_;
 175
 176       if (direction_)
 177         queue_ptr_ = queue_ptr_.next_;
 178       else
 179         queue_ptr_ = queue_ptr_.prev_;
 180
 181       return data;
 182     }
 183
 184   public boolean hasMoreElements()
 185     {
 186       return queue_ptr_ != null;
 187     }
 188 }