Parse A Regular Expression

Regexp.java

package parser;

public class ExpressionNode {

	public static final char or = '|';
	public static final char and = '.';
	public static final char repeat = '*';

	public char symbol;
	public ExpressionNode left, right;

	public static boolean parse(String string, ExpressionNode expression) {
		if (expression.symbol == or) {
			boolean result = false;
			for (int i = 0; i < string.length() + 1; i++) {
				result |= parse(string, expression.left)
						|| parse(string, expression.right);
			}
			return result;
		} else if (expression.symbol == and) {
			boolean result = false;
			for (int i = 0; i < string.length() + 1; i++) {
				result |= parse(string.substring(0, i), expression.left)
						&& parse(string.substring(i, string.length()),
								expression.right);
			}
			return result;
		} else if (expression.symbol == repeat) {
			if (string.length() > 0) {
				int match = -1;
				for (int i = 0; i < string.length() + 1; i++) {
					if (parse(string.substring(0, i), expression.left)) {
						match = i;
					}
				}
				if(match < 0) {
					return false;
				}
				return parse(string.substring(match, string.length()),expression);
			}
			return true;
		} else {
			return string.length() == 1 && string.charAt(0) == expression.symbol;
		}
	}

	public static void main(String[] args) {
		ExpressionNode a = new ExpressionNode();
		a.symbol = 'a';
		ExpressionNode b = new ExpressionNode();
		b.symbol = 'b';
		ExpressionNode ab = new ExpressionNode();
		ab.symbol = ExpressionNode.and;
		ab.left = a;
		ab.right = b;
		System.out.println(parse("ab", ab));
		System.out.println(parse("acb", ab));
		System.out.println(parse("abb", ab));
		System.out.println(parse("a", ab));
		System.out.println(parse("b", ab));
		ExpressionNode abn = new ExpressionNode();
		abn.symbol = ExpressionNode.repeat;
		abn.left = ab;
		System.out.println(parse("ab", abn));
		System.out.println(parse("abc", abn));
		System.out.println(parse("abab", abn));
		System.out.println(parse("ababab", abn));

	}
}