qdemo.java

Mcgraw-Hill - Java 2 - A Beginner S Guide, 2Nd Ed - 2003 -prog.

/* 
   Project 5-2 
 
   A queue class for characters. 
*/ 
 
class Queue { 
  char q[]; // this array holds the queue 
  int putloc, getloc; // the put and get indices 
 
  Queue(int size) { 
    q = new char[size+1]; // allocate memory for queue 
    putloc = getloc = 0; 
  } 
 
  // put a characer into the queue 
  void put(char ch) { 
    if(putloc==q.length-1) { 
      System.out.println(" -- Queue is full."); 
      return; 
    } 
     
    putloc++; 
    q[putloc] = ch; 
  } 
 
  // get a character from the queue 
  char get() { 
    if(getloc == putloc) { 
      System.out.println(" -- Queue is empty."); 
      return (char) 0;  
    } 
   
    getloc++; 
    return q[getloc]; 
  } 
} 
 
// Demonstrate the Queue class. 
class QDemo { 
  public static void main(String args[]) { 
    Queue bigQ = new Queue(100); 
    Queue smallQ = new Queue(4); 
    char ch; 
    int i; 
 
    System.out.println("Using bigQ to store the alphabet."); 
    // put some numbers into bigQ 
    for(i=0; i < 26; i++) 
      bigQ.put((char) ('A' + i)); 
 
    // retrieve and display elements from bigQ 
    System.out.print("Contents of bigQ: "); 
    for(i=0; i < 26; i++) {  
      ch = bigQ.get(); 
      if(ch != (char) 0) System.out.print(ch); 
    } 
 
    System.out.println("\n"); 
 
 
    System.out.println("Using smallQ to generate erros."); 
    // Now, use smallQ to generate some errors 
    for(i=0; i < 5; i++) { 
      System.out.print("Attempting to store " + 
                       (char) ('Z' - i)); 
 
      smallQ.put((char) ('Z' - i)); 
 
      System.out.println(); 
    } 
    System.out.println(); 
 
    // more errors on smallQ 
    System.out.print("Contents of smallQ: "); 
    for(i=0; i < 5; i++) {  
      ch = smallQ.get(); 
 
      if(ch != (char) 0) System.out.print(ch); 
    } 
  } 
}