How to check if a String is balanced?

Question

I want to test if an input String is balanced. It would be balanced if there is a matching opening and closing parenthesis, bracket or brace.

example:
{} bal         


        

Answer 1

import java.util.Stack;

public class SyntaxChecker {

    /**
     * This enum represents all types of open brackets. If we have a new type then
     * just add it to this list with the corresponding closed bracket in the other
     * ClosedBracketTypes enum  
     * @author AnishBivalkar
     *
     */
    private enum OpenBracketTypes {
        LEFT_ROUND_BRACKET('('),
        LEFT_SQUARE_BRACKET('['),
        LEFT_CURLY_BRACKET('{');

        char ch;

        // Constructs the given bracket type
        OpenBracketTypes(char ch) {
            this.ch = ch;
        }

        // Getter for the type of bracket
        public final char getBracket() {
            return ch;
        }


        /**
         * This method checks if the current character is of type OpenBrackets
         * @param name
         * @return True if the current character is of type OpenBrackets, false otherwise
         */
        public static boolean contains(final char name) {
            for (OpenBracketTypes type : OpenBracketTypes.values()) {
                if (type.getBracket() == name) {
                    return true;
                }
            }

            return false;
        }
    }

    /**
     * This enum represents all types of Closed brackets. If we have a new type then
     * just add it to this list with the corresponding open bracket in the other
     * OpenBracketTypes enum    
     * @author AnishBivalkar
     *
     */
    private enum CloseBracketTypes {
        RIGHT_ROUND_BRACKET(')'),
        RIGHT_SQUARE_BRACKET(']'),
        RIGHT_CURLY_BRACKET('}');

        char ch;
        CloseBracketTypes(char ch) {
            this.ch = ch;
        }

        private char getBracket() {
            return ch;
        }

        /**
         * This method checks if a given bracket type is a closing bracket and if it correctly
         * completes the opening bracket
         * @param bracket
         * @param brackets
         * @return
         */
        public static boolean isBracketMatching(char bracket, Stack brackets) {
            // If the current stack is empty and we encountered a closing bracket then this is
            // an incorrect syntax
            if (brackets.isEmpty()) {
                return false;
            } else {
                if (bracket == CloseBracketTypes.RIGHT_ROUND_BRACKET.getBracket()) {
                    if (brackets.peek() == OpenBracketTypes.LEFT_ROUND_BRACKET.getBracket()) {
                        return true;
                    }
                } else if (bracket == CloseBracketTypes.RIGHT_SQUARE_BRACKET.ch) {
                    if (brackets.peek() == OpenBracketTypes.LEFT_SQUARE_BRACKET.getBracket()) {
                        return true;
                    }
                } else if (bracket == CloseBracketTypes.RIGHT_CURLY_BRACKET.ch) {
                    if (brackets.peek() == OpenBracketTypes.LEFT_CURLY_BRACKET.getBracket()) {
                        return true;
                    }
                }

                return false;
            }
        }

        /**
         * This method checks if the current character is of type ClosedBrackets
         * @param name
         * @return true if the current character is of type ClosedBrackets, false otherwise
         */
        public static boolean contains(final char name) {
            for (CloseBracketTypes type : CloseBracketTypes.values()) {
                if (type.getBracket() == name) {
                    return true;
                }
            }

            return false;
        }
    }


    /**
     * This method check the syntax for brackets. There should always exist a
     * corresponding closing bracket for a open bracket of same type.
     * 
     * It runs in O(N) time with O(N) worst case space complexity for the stack
     * @param sentence The string whose syntax is to be checked
     * @return         True if the syntax of the given string is correct, false otherwise
     */
    public static boolean matchBrackets(String sentence) {
        boolean bracketsMatched = true;

        // Check if sentence is null
        if (sentence == null) {
            throw new IllegalArgumentException("Input cannot be null");
        }

        // Empty string has correct syntax
        if (sentence.isEmpty()) {
            return bracketsMatched;
        } else {
            Stack brackets = new Stack();
            char[] letters = sentence.toCharArray();

            for (char letter : letters) {

                // If the letter is a type of open bracket then push it 
                // in stack else if the letter is a type of closing bracket 
                // then pop it from the stack
                if (OpenBracketTypes.contains(letter)) {
                    brackets.push(letter);
                } else if (CloseBracketTypes.contains(letter)) {
                    if (!CloseBracketTypes.isBracketMatching(letter, brackets)) {
                        return false;
                    } else {
                        brackets.pop();
                    }
                }
            }

            // If the stack is not empty then the syntax is incorrect
            if (!brackets.isEmpty()) {
                bracketsMatched = false;
            }
        }

        return bracketsMatched;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        String words = "[[][][]Anfield[[]([])[]]becons()]";
        boolean isSyntaxCorrect = SyntaxChecker.matchBrackets(words);

        if (isSyntaxCorrect) {
            System.out.println("The syntax is correct");
        } else {
            System.out.println("Incorrect syntax");
        }
    }
}

Any feedback on this is most welcome. Please criticize if you find something is wrong or useless. I am just trying to learn.