Queue.java

package org.arabidopsis.ahocorasick;

import java.util.ArrayList;

/**
 * Quick-and-dirty queue class. Essentially uses two lists to represent a queue.
 */
class Queue<T> {
  ArrayList<T> l1;
  ArrayList<T> l2;

  public Queue() {
    l1 = new ArrayList<T>();
    l2 = new ArrayList<T>();
  }

  public void add(T s) {
    l2.add(s);
  }

  public boolean isEmpty() {
    return l1.isEmpty() && l2.isEmpty();
  }

  public T pop() {
    if (isEmpty())
      throw new IllegalStateException("Popping empty queue.");

    if (l1.isEmpty()) {
      for (int i = l2.size() - 1; i >= 0; i--)
        l1.add(l2.remove(i));

      assert l2.isEmpty();
      assert !l1.isEmpty();
    }

    return l1.remove(l1.size() - 1);
  }
}