Java实现四则运算表达式计算

Java实现四则运算表达式计算

1. /** 
2.  * 四则运算表达式计算 
3.  * @author penli 
4.  * 
5.  */  
6. public class Arithmetic {  
7.     public static void main(String args[]){  
8.         System.out.println(arithmetic("2.2+((3+4)*2-22)/2*3.2"));  
9.     }  
10.     public static double arithmetic(String exp){  
11.         String result = parseExp(exp).replaceAll("[\\[\\]]", "");  
12.         return Double.parseDouble(result);  
13.     }  
14.     /** 
15.      * 解析计算四则运算表达式，例：2+((3+4)*2-22)/2*3 
16.      * @param expression 
17.      * @return 
18.      */  
19.     public static String parseExp(String expression){  
20.         //String numberReg="^((?!0)\\d+(\\.\\d+(?<!0))?)|(0\\.\\d+(?<!0))$";   
21.         expression=expression.replaceAll("\\s+", "").replaceAll("^\\((.+)\\)$", "$1");  
22.         String checkExp="\\d";  
23.         String minExp="^((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\+\\-\\*\\/]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))$";  
24.         //最小表达式计算   
25.         if(expression.matches(minExp)){  
26.             String result=calculate(expression);  
27.               
28.             return Double.parseDouble(result)>=0?result:"["+result+"]";  
29.         }  
30.         //计算不带括号的四则运算   
31.         String noParentheses="^[^\\(\\)]+$";  
32.         String priorOperatorExp="(((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\*\\/]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\])))";  
33.         String operatorExp="(((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\+\\-]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\])))";  
34.         if(expression.matches(noParentheses)){  
35.             Pattern patt=Pattern.compile(priorOperatorExp);  
36.             Matcher mat=patt.matcher(expression);  
37.             if(mat.find()){  
38.                 String tempMinExp=mat.group();  
39.                 expression=expression.replaceFirst(priorOperatorExp, parseExp(tempMinExp));  
40.             }else{  
41.                 patt=Pattern.compile(operatorExp);  
42.                 mat=patt.matcher(expression);  
43.                   
44.                 if(mat.find()){  
45.                     String tempMinExp=mat.group();  
46.                     expression=expression.replaceFirst(operatorExp, parseExp(tempMinExp));  
47.                 }  
48.             }  
49.             return parseExp(expression);  
50.         }  
51.         //计算带括号的四则运算   
52.         String minParentheses="\\([^\\(\\)]+\\)";  
53.         Pattern patt=Pattern.compile(minParentheses);  
54.         Matcher mat=patt.matcher(expression);  
55.         if(mat.find()){  
56.             String tempMinExp=mat.group();  
57.             expression=expression.replaceFirst(minParentheses, parseExp(tempMinExp));  
58.         }  
59.         return parseExp(expression);  
60.     }  
61.     /** 
62.      * 计算最小单位四则运算表达式（两个数字） 
63.      * @param exp 
64.      * @return 
65.      */  
66.     public static String calculate(String exp){  
67.         exp=exp.replaceAll("[\\[\\]]", "");  
68.         String number[]=exp.replaceFirst("(\\d)[\\+\\-\\*\\/]", "$1,").split(",");  
69.         BigDecimal number1=new BigDecimal(number[0]);  
70.         BigDecimal number2=new BigDecimal(number[1]);  
71.         BigDecimal result=null;  
72.           
73.         String operator=exp.replaceFirst("^.*\\d([\\+\\-\\*\\/]).+$", "$1");  
74.         if("+".equals(operator)){  
75.             result=number1.add(number2);  
76.         }else if("-".equals(operator)){  
77.             result=number1.subtract(number2);  
78.         }else if("*".equals(operator)){  
79.             result=number1.multiply(number2);  
80.         }else if("/".equals(operator)){  
81.             result=number1.divide(number2);  
82.         }  
83.           
84.         return result!=null?result.toString():null;  
85.     }  
86. }