682. Baseball Game

class Solution {
			public int calPoints(String[] ops) {
		int currentSum = 0;
		ArrayList valid = new ArrayList();
		for (int i = 0; i < ops.length; i++) {

			if (ops[i].equals("C")) {
				currentSum -= new Integer(valid.get(valid.size() - 1));
				valid.remove(valid.size() - 1);
			} else if (ops[i].equals("D")) {
				int newScore = (2 * valid.get(valid.size() - 1));
				currentSum += newScore;
				valid.add(newScore);
			} else if (ops[i].equals("+")) {
				int newScore = new Integer(valid.get(valid.size() - 1)) + new Integer((valid.get(valid.size() - 2)));
				currentSum += newScore;
				valid.add(newScore);
			} else {
				valid.add(new Integer(ops[i]));
				currentSum += new Integer(ops[i]);
			}
		}
		return currentSum;

	}
}