Peek() and remove() methods for Queue implementation in Blackberry

Question

Hi,

I want to implement peek and remove methods , similar to Java's Queue.peek() and Queue.remove() , in Blackberry application. I have a custom queue implementation ,but how do I get peek elements and remove elements from queue?

Please help,

Thanks in advance.

Answer 1

Try to use Arrays class... if you need to peek, take last element from Object array, to remove just delete last one:

class Queue {
    private Object[] mElements = new Object[] {};

    public void enqueue(Object element) {
     Arrays.insertAt(mElements, element, 0);
    }

    public Object dequeue() {
     Object result = null;
     if (null != mElements && 0 < mElements.length) {
      result = mElements[mElements.length - 1];
      Arrays.remove(mElements, result);
     }
     return result;
    }

    public Object peek() {
     if (null != mElements && 0 < mElements.length)
      return mElements[mElements.length - 1];
     else
      return null;
    }

    public void remove() {
     if (null != mElements && 0 < mElements.length)
      Arrays.remove(mElements, peek());
    }
}

Using example:

class Scr extends MainScreen {
    public Scr() {
     Queue queue = new Queue();
     queue.enqueue(new String("3"));   
     queue.enqueue(new Boolean(true));
     queue.enqueue(new Integer(1));  
     //see "3" in console
     System.out.println(queue.peek());
     //see "3" still there
     System.out.println(queue.peek());
     //remove "3"
     queue.remove();
     //see "true" in console
     System.out.println(queue.peek());  
     //dequeue all elements
     Object element = null;
     while ((element = queue.dequeue()) != null) {
      System.out.println(element.toString());
     }
    }
}

Answer 2

You should be able to use a Vector to do these types of operations - firstElement() to peek at the first in the list, lastElement() to peek at the last, or elementAt() to look at anything in between. Then use removeElementAt() to remove an element.

Answer 3

Hi, I am using above code successfully for queue manipulations. I need to add element at first location (addBefore in Java) .

How can I do it?

Please help