package algs13;
import stdlib.*;
public class XFixedCapacityStackOfStrings {
  private String[] a; // holds the items
  private int N;      // number of items in stack
  // Invariant (after the constructor):
  //   a[0]..a[N-1] are non null
  //   a[N]..a[a.length-1] are null
  public XFixedCapacityStackOfStrings (int capacity) {
    this.a = new String[capacity];
    this.N = 0;
  }
  public int size ()        { return N; }
  public boolean isEmpty () { return (N == 0); }
  public void push (String item) {
    if (item == null) throw new IllegalArgumentException ();
    if (N >= a.length) throw new RuntimeException ("Stack full");
    a[N] = item;
    N++;
  }
  public String pop () {
    if (N <= 0) throw new RuntimeException ("Stack empty");
    N--;
    String result = a[N];
    a[N] = null;
    return result;
  }

  public static void main(String[] args) {
    //Trace.showObjectIdsRedundantly (true);
    Trace.showBuiltInObjects(true);
    //Trace.drawStepsOfMethod ("main");
    Trace.drawSteps ();
    Trace.run ();
    XFixedCapacityStackOfStrings stack1 = new XFixedCapacityStackOfStrings (7);
    XFixedCapacityStackOfStrings stack2 = new XFixedCapacityStackOfStrings (3);
    stack1.push ("a");
    stack2.push ("b");
    stack1.push ("c");
    stack2.push ("d");
    stack1.push ("e");
    stack2.push ("f");
    stack1.push ("g");
    while (!stack2.isEmpty()) {
      StdOut.println (stack2.pop ());
    }
    StdOut.println();
    while (!stack1.isEmpty()) {
      StdOut.println (stack1.pop ());
    }
  }
}