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Java實現四則運算表達式計算

/**
* 四則運算表達式計算
* @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);
}
/**
* 解析計算四則運算表達式，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))$";
expression=expression.replaceAll("\\s+", "").replaceAll("^\$(.+)\$$", "$1");
String checkExp="\\d";
String minExp="^((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))[\\+\\-\\*\\/]((\\d+(\\.\\d+)?)|(\\[\\-\\d+(\\.\\d+)?\\]))$";
//最小表達式計算
if(expression.matches(minExp)){
String result=calculate(expression);
return Double.parseDouble(result)>=0?result:"["+result+"]";
}
//計算不帶括號的四則運算
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);
}
//計算帶括號的四則運算
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);
}
/**
* 計算最小單位四則運算表達式（兩個數字）
* @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;
}
}

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