FixedCapacityStack.java

Below is the syntax highlighted version of FixedCapacityStack.java from §1.3 Stacks and Queues.

/******************************************************************************
 *  Compilation:  javac FixedCapacityStack.java
 *  Execution:    java FixedCapacityStack
 *  Dependencies: StdIn.java StdOut.java
 *
 *  Generic stack implementation with a fixed-size array.
 *
 *  % more tobe.txt
 *  to be or not to - be - - that - - - is
 *
 *  % java FixedCapacityStack 5 < tobe.txt
 *  to be not that or be
 *
 *  Remark:  bare-bones implementation. Does not do repeated
 *  doubling or null out empty array entries to avoid loitering.
 *
 ******************************************************************************/

import java.util.Iterator;
import java.util.NoSuchElementException;

public class FixedCapacityStack<Item> implements Iterable<Item> {
    private Item[] a;    // holds the items
    private int n;       // number of items in stack

    // create an empty stack with given capacity
    public FixedCapacityStack(int capacity) {
        a = (Item[]) new Object[capacity];   // no generic array creation
        n = 0;
    }

    public boolean isEmpty() {
        return n == 0;
    }

    public void push(Item item) {
        a[n++] = item;
    }

    public Item pop() {
        return a[--n];
    }

    public Iterator<Item> iterator() {
        return new ReverseArrayIterator();
    }

    // an array iterator, in reverse order
    public class ReverseArrayIterator implements Iterator<Item> {
        private int i = n-1;

        public boolean hasNext() {
            return i >= 0;
        }

        public Item next() {
            if (!hasNext()) throw new NoSuchElementException();
            return a[i--];
        }
    }


    public static void main(String[] args) {
        int max = Integer.parseInt(args[0]);
        FixedCapacityStack<String> stack = new FixedCapacityStack<String>(max);
        while (!StdIn.isEmpty()) {
            String item = StdIn.readString();
            if (!item.equals("-")) stack.push(item);
            else if (stack.isEmpty())  StdOut.println("BAD INPUT");
            else                       StdOut.print(stack.pop() + " ");
        }
        StdOut.println();

        // print what's left on the stack
        StdOut.print("Left on stack: ");
        for (String s : stack) {
            StdOut.print(s + " ");
        }
        StdOut.println();
    }
}