QueueArray.java

//Vrsta s poljem
 
public class QueueArray implements Queue {
  static final int DEFAULT_LENGTH = 100 ;
  private Object elements[] ;
  private int front, rear ;
 
  public QueueArray() {
    this(DEFAULT_LENGTH) ;
  }
  public QueueArray(int noElem) {
    elements = new Object[noElem] ;
    makenull() ;
  }
  public void makenull() {
    front = 0 ;
    rear = elements.length - 1 ;
  }
 
  public boolean empty() {
    return incr(rear)==front ;
  }
 
  public Object front() throws Underflow {
    if (empty()) // error
       throw new Underflow() ;
    return elements[front] ;
  }
  public void enqueue(Object x) throws Overflow {
    if (incr(incr(rear))==front) //error: full queue
      throw new Overflow() ;
    else {
      rear=incr(rear) ;
      elements[rear] = x ;
    }
  }
  public void dequeue() throws Underflow {
    if (empty()) // error
      throw new Underflow() ;
    else front = incr(front) ;
  }
 
  private int incr(int pos) {
    return (pos+1) % elements.length ;
  }
 
  public static void main(String[] args) {
    QueueArray q = new QueueArray();
    System.out.println("Testing class "+q.getClass() );
    int i ;
    try {
      for (i = 1; i <= 5; i++) {
        q.enqueue(new Integer(i));
        System.out.println("Enqueing " + i);
      }
      while (!q.empty()) {
        System.out.println("Dequeing " + q.front());
        q.dequeue();
      }
    }
    catch (Underflow e) {
      System.out.println("Dequeing an empty queue in "+q.getClass());
    }
    catch (Overflow e) {
      System.out.println("Queue is already full in "+q.getClass());
    }
  }
}