import java.util.NoSuchElementException;


public class TokenArrayStack implements TokenStack {
	
	private Token[] tarray;
	private int count; 
	
	/**
	 * Default Token Array Stack constructor
	 *
	 */
	public TokenArrayStack(){
		this(10);
	}
	
	public TokenArrayStack(int size){
		tarray = new Token[size];
		count = 0;
	}

  /**
   * Tells if the stack is empty.
   *
   * @return <code>true</code> if the stack is empty, <code>false</code>
   *         otherwise.
   */
	public boolean isEmpty() {
		if(count == 0) return true;
		return false;
	}

  /**
   * Returns the token at the top of the stack.
   *
   * @return the {@link Token} instance at the top of the stack
   * @throws java.util.NoSuchElementException
   *             if the stack is empty
   */
	public Token peek() {
		if(isEmpty()){
			throw new NoSuchElementException();
		}
		else {
			return tarray[0];
		}
	}

  /**
   * Removes and returns the token at the top of the stack.
   *
   * @return the {@link Token} instance at the top of the stack
   * @throws java.util.NoSuchElementException
   *             if the stack is empty
   */
	public Token pop() {
		if(isEmpty()){
			throw new NoSuchElementException();
		}
		else {
			return tarray[count--];
		}
	}


  /**
   * Adds the given token to the top of the stack.
   *
   * @param elem the {@link Token} instance that must be added
   * @return     the <code>Token</code> instance that was added
   */
	public Token push(Token elem) {
		if(count == tarray.length) {
			Token[] newarray = new Token[2*tarray.length];
			for(int i = 0; i < tarray.length; i++){
				newarray[i] = tarray[i];
			}
			tarray = newarray;
		}
		tarray[++count] = elem;
		return elem;
	}

  /**
   * Returns the size of the stack.
   *
   * @return a non-negative number
   */
	public int size() {
		return count;
	}

}