Java实现四则运算表达式计算
/** * 四则运算表达式计算 * @author penli * */public class Arithmetic {public static void main(String args[]){System.out.println(arithmetic("2.2+((3+4)*2-22)/2*3.2"));}public static double arithmetic(String exp){String result = parseExp(exp).replaceAll("[\\[\\]]", "");return Double.parseDouble(result);}/** * 解析计算四则运算表达式，例：2+((3+4)*2-22)/2*3 * @param expression * @return */public static String parseExp(String expression){//String numberReg="^((?!0)\\d+(\\.\\d+(?<!0))?)|(0\\.\\d+(?<!0))$";expression=expression.replaceAll("\\s+", "").replaceAll("^\\((.+)\\)$", "$1");String checkExp="\\d";String minExp="^((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\+\\-\\*\\/]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))$";//最小表达式计算if(expression.matches(minExp)){String result=calculate(expression);return Double.parseDouble(result)>=0?result:"["+result+"]";}//计算不带括号的四则运算String noParentheses="^[^\\(\\)]+$";String priorOperatorExp="(((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\*\\/]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\])))";String operatorExp="(((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\+\\-]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\])))";if(expression.matches(noParentheses)){Pattern patt=Pattern.compile(priorOperatorExp);Matcher mat=patt.matcher(expression);if(mat.find()){String tempMinExp=mat.group();expression=expression.replaceFirst(priorOperatorExp, parseExp(tempMinExp));}else{patt=Pattern.compile(operatorExp);mat=patt.matcher(expression);if(mat.find()){String tempMinExp=mat.group();expression=expression.replaceFirst(operatorExp, parseExp(tempMinExp));}}return parseExp(expression);}//计算带括号的四则运算String minParentheses="\\([^\\(\\)]+\\)";Pattern patt=Pattern.compile(minParentheses);Matcher mat=patt.matcher(expression);if(mat.find()){String tempMinExp=mat.group();expression=expression.replaceFirst(minParentheses, parseExp(tempMinExp));}return parseExp(expression);}/** * 计算最小单位四则运算表达式（两个数字） * @param exp * @return */public static String calculate(String exp){exp=exp.replaceAll("[\\[\\]]", "");String number[]=exp.replaceFirst("(\\d)[\\+\\-\\*\\/]", "$1,").split(",");BigDecimal number1=new BigDecimal(number[0]);BigDecimal number2=new BigDecimal(number[1]);BigDecimal result=null;String operator=exp.replaceFirst("^.*\\d([\\+\\-\\*\\/]).+$", "$1");if("+".equals(operator)){result=number1.add(number2);}else if("-".equals(operator)){result=number1.subtract(number2);}else if("*".equals(operator)){result=number1.multiply(number2);}else if("/".equals(operator)){result=number1.divide(number2);}return result!=null?result.toString():null;}}