Queue in Java using Array Data Structure



@author sibyjosek@gmail.com

The Queue Class

public class Queue { // outer class
       class Data{    // an inner class
             int d;
void show(){
                  System.out.print(" (" + d + ") ");
             }
             Data(int x){ d=x;}
       }
      Data q[];
      int front, rear;
      int mSize;
      final String nullQ = "Empty Queue !!!",
                   fullQ = "...Queue is Full !!!";
      public Queue(int maximumSize){
           mSize=maximumSize;
           q=new Data[mSize];
           front=rear=-1;
      }
      boolean isEmpty(){ return front==-1;  }
      boolean isFull(){ return front != -1 & (rear+1) % mSize == front; }
 
      Data first() throws Throwable{
           if (isEmpty()) throw new Throwable(nullQ);
           return q[front];
      }
      Data last() throws Throwable{
           if (isEmpty()) throw new Throwable(nullQ);
           return q[rear];
      }
      void add(Data data) throws Throwable{
           if(front==-1)
              front=rear=0;
           else{
              if (isFull()) throw new Throwable(fullQ);
              rear = (rear + 1) % mSize;
           }
           q[rear]=data;
      }
      void add(int data) throws Throwable{
           add(new Data(data));
      }
      Data delete() throws Throwable{
           if(isEmpty()) throw new Throwable(nullQ);
           Data d=q[front];
           if(front==rear)
              front=rear=-1;
           else
              front = (front + 1) % mSize;
           return d;
      }
      void show()throws Throwable{
        if(isEmpty()) throw new Throwable(nullQ);
        System.out.println();
        int i=front;
        do{
          if( i == rear){
              q[i].show();
              break;
          }
          q[i].show();
          i++;
          i %= mSize;
     }while(true);
   }

   protected void finalize() throws Throwable {
      super.finalize();
      q=null;
  }
}
Main - The Test Driver Class


public class Main {
 public static void main(String[] args) {
  Queue q=new Queue (5);
  try{
   q.add(10);
   q.add(55);
   q.add(66);
   q.add(13);
   q.add(5);
   q.add(10001);
  }catch (Throwable e) {
   System.out.println(e.getMessage());
  }
  try{
   q.show();   //show current queue
   System.out.println("\nDeleting");
   q.delete().show();  // show deleted item
   q.delete().show();
   q.delete().show();
   q.delete().show();
   q.delete().show(); // all 5 items removed
   q.add(555555);
   q.add(555);
   q.add(5);
   System.out.println("\nNew Queue ");
   q.show();         // show current queue
  }catch (Throwable e) {
   System.out.println(e.getMessage());
  }
 }
}
The Output


...Queue is Full !!!

 (10)  (55)  (66)  (13)  (5) 
Deleting
 (10)  (55)  (66)  (13)  (5) 
New Queue 

 (555555)  (555)  (5)
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