Java determines whether a string is a valid bracket

Given a string s that only includes '(', ')', '{', '}', '[', ']', determine whether the string is valid.
To be a valid string,
the opening bracket must be closed by a closing bracket of the same type. For example: "[]", "()", "{}"
The left brackets must be closed in the correct order. For example: "[()]"
Each right bracket has a corresponding left bracket of the same type. For example:"[()]{}"

package learnProject.csdn;

/**
 * 
 * @author Roc-xb
 *
 */
public class ValidParentheses {

	public static boolean isValid(String s) {
		if (s == null || s.length() == 0)
			return false;
		char[] stack = new char[s.length()];
		int head = 0;
		for (char c : s.toCharArray()) {
			switch (c) {
			case '{':
			case '[':
			case '(':
				stack[head++] = c;
				break;
			case '}':
				if (head == 0 || stack[--head] != '{') {
					return false;
				}
				break;
			case ')':
				if (head == 0 || stack[--head] != '(') {
					return false;
				}
				break;
			case ']':
				if (head == 0 || stack[--head] != '[') {
					return false;
				}
				break;
			}
		}
		return head == 0;
	}

	public static void main(String[] args) {
		System.out.println(isValid(null));

	}
}