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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. class GenericResizingStack<Item> implements Iterable<Item> {
  8. 	private Item[] s;
  9. 	private int n = 0;
  10.  
  11. 	public GenericResizingStack (int capacity) {
  12. 		// @#$*! generic array creation: s = new Item[capacity]; not allowed!
  13. 		s = (Item[]) new Object[capacity]; // So ugly cast needed
  14. 	}
  15.  
  16. 	public void push (Item item) {
  17. 		if (n == s.length) resize (2 * s.length); 
  18. 		s [n++] = item;
  19. 	}
  20.  
  21. 	public Item pop() {
  22. 		Item item = s[--n];
  23. 		s[n] = null;
  24. 		if (n > 0 && n == s.length/4) resize(s.length/2);
  25. 		return item;
  26. 	}
  27.  
  28. 	private void resize(int capacity) { 
  29. 		Item[] copy = (Item[]) new Object[capacity];
  30. 		for (int i = 0; i < n; i++) copy[i] = s[i];
  31. 		s = copy;
  32. 	}
  33.  
  34. 	public Iterator<Item> iterator() {
  35. 		return new ReverseArrayIterator(); // Reverse to print in order of popping
  36. 	}
  37.  
  38. 	private class ReverseArrayIterator implements Iterator<Item> {
  39. 		private int i = n-1;
  40.  
  41. 		public boolean hasNext() {
  42. 			return i >=0;
  43. 		}
  44.  
  45. 		public Item next() {
  46. 			if (!hasNext ()) throw new NoSuchElementException();
  47. 			return s[i--];
  48. 		}
  49. 	}
  50. }
  51.  
  52.  
  53. /* Name of the class has to be "Main" only if the class is public. */
  54. public class Main
  55. {
  56. 	public static void main (String[] args) throws java.lang.Exception
  57. 	{
  58. 		GenericResizingStack<String> strStack = new GenericResizingStack<String>(1);
  59. 		strStack.push("Cat");
  60. 		strStack.push("Dog");
  61.  
  62. 		System.out.println("Iterating:");
  63. 		for (String s : strStack) System.out.println(s);
  64.  
  65. 		System.out.println("Popping:");
  66. 		System.out.println(strStack.pop());
  67. 		System.out.println(strStack.pop());
  68. 	}
  69. }
Success #stdin #stdout 0.09s 54620KB
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Standard input is empty
stdout
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Iterating:
Dog
Cat
Popping:
Dog
Cat
https://ideone.com/KiIxFL
Stack with resizing array and iterator
language:
Java (HotSpot 12)
created:
3 days ago
visibility:
public

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