dsa

Data Structures & Algorithms - Spring 2018
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StackRA.java (1709B)

      1 package collections;
      2 
      3 public class StackRA<T> implements StackInterface<T>{
      4 
      5     protected T []items;
      6     protected int numItems;
      7 
      8     public StackRA() {
      9         items = (T[]) new Object[3];
     10         numItems = 0;
     11     }
     12 
     13     public boolean isEmpty() {
     14         return (numItems == 0);
     15     }
     16 
     17     public int size() {
     18         return numItems;
     19     }
     20 
     21     public void popAll() {
     22         items = (T[]) new Object[3];
     23         numItems = 0;
     24     }
     25 
     26     public void push (T item)
     27             throws StackException {
     28 
     29         if (numItems == items.length) {
     30             resize();
     31         }
     32         items[numItems++] = item;
     33     }
     34 
     35     public T pop()
     36             throws StackException {
     37         if (numItems != 0) {
     38             T item = items[numItems -1];
     39             items[numItems-1] = null;
     40             numItems --;
     41             return item;
     42         }
     43         else {
     44             throw new StackException("StackException: Stack is empty on pop()");
     45         }
     46     }
     47 
     48     public T peek()
     49             throws StackException {
     50         if (numItems != 0) {
     51             return items[numItems - 1];
     52         }
     53         else {
     54             throw new StackException("StackException: Stack is empty on peek()");
     55         }
     56     }
     57 
     58     public void resize() {
     59         T []tmp;
     60         tmp = (T[]) new Object[numItems*2 + 1];
     61         for (int i = 0; i < items.length; i++) {
     62             tmp[i] = items[i];
     63         }
     64         items = tmp;
     65     }
     66 
     67     @Override
     68     public String toString() {
     69         String result = "Stack of size " + numItems + " has the following items : ";
     70 
     71         for (int i = 0; i < numItems; i++) {
     72             if (items[i] != null)
     73                 result += items[i] + " ";
     74         }
     75 
     76         return result;
     77     }
     78 
     79 }