Tokenizer类中用到的平衡符号的Balance类

作用：检查括号的开关是否正确，如果有错误，返回错误的第几行和总共有几处错误

package com.tokenizer.cc;

import java.io.Reader;
import java.util.Stack;
/**
 * Balance class: check for balanced symbols
 * @author SunnyBoy
 * @version Time：2017年8月5日 上午10:39:08
 */
public class Balance {
    private Tokenizer tok;
    private int errors;

    public Balance(Reader inStream) {
        errors = 0;
        tok = new Tokenizer(inStream);
    }
    /**
     * Print an error message for unbalanced symbols.
     * @return number of errors detected.
     */
    public int checkBalance() {
        char ch;
        Symbol match = null;
        Stack pendingTokens = new Stack();

        while ((ch = tok.getNextOpenClose()) != '\0') {
            Symbol lastSymbol = new Symbol(ch, tok.getLineNumber());
            switch (ch) {
            case '(':
            case '[':
            case '{':
                pendingTokens.push(lastSymbol);
                break;
            case ')':
            case ']':
            case '}':
                if (pendingTokens.isEmpty()) {
                    errors++;
                    System.out.println("Extraneous " + ch + " at line " + tok.getLineNumber());
                    ;
                } else {
                    match = pendingTokens.pop();
                    checkMath(match, lastSymbol);
                }
                break;
            default:
                break;
            }
        }
        while (!pendingTokens.isEmpty()) {
            match = pendingTokens.pop();
            System.out.println("Unmatched " + match.token + " at line " + match.theLine);
            errors++;
        }
        return errors + tok.getErrorCount();
    }
    /**
     * Print an error message if clSym does not match opSym.
     * Update errors.
     * @param opSym
     * @param clSym
     */
    private void checkMath(Symbol opSym, Symbol clSym) {
        if (opSym.token == '(' && clSym.token != ')' || opSym.token == '[' && clSym.token != ']'
                || opSym.token == '{' && clSym.token != '}') {
            System.out.println("Found " + clSym.token + " on line " + tok.getLineNumber() + "; does not match "
                    + opSym.token + " at line " + opSym.theLine);
            errors++;
        }
    }
    /**
     * Symbol nested class;
     * represents what will be placed on the stack.
     */
    private static class Symbol {
        public char token;
        public int theLine;

        public Symbol(char tok, int line) {
            token = tok;
            theLine = line;
        }
    }
}