public class Arithmetic {
public Arithmetic() {
}
/*操作区*/
private double operation(double n1,double n2,String expression){
if(expression.equals("+")){
return n1 + n2;
} else if(expression.equals("-")){
return n1 - n2;
} else if(expression.equals("*")){
return n1 * n2;
} else if(expression.equals("/")){
return n1 / n2;
}
return 0;
}
/*优先级*/
private int priority(String expression){
if(expression.equals("+") || expression.equals("-")){
return 0;
} else if(expression.equals("*") || expression.equals("/")){
return 1;
} else {
return -1;
}
}
/**
* 判断是否为一个算数运算符
* @param expression 算式运算符
* @return
*/
private boolean isExpression(String expression){
return expression.equals("+") || expression.equals("-") || expression.equals("*") || expression.equals("/") ;
}
/**
* 计算入口
* @param numModel 算式
* @return 结果
*/
public double doAccount(String numModel){
int endIndex = 0;
int startIndex = numModel.indexOf("(",endIndex);
while(startIndex != -1){
endIndex = numModel.indexOf(")", startIndex) + 1;
String segment = numModel.substring(startIndex,endIndex);
double tResult = account(segment.replace("(","").replace(")",""));
numModel = numModel.replace(segment,String.valueOf(tResult));
startIndex = numModel.indexOf("(",0);
}
DecimalFormat format = new DecimalFormat("0.##");
return Double.parseDouble(format.format(account(numModel)));
}
/**
* 核心算法逻辑
* @param numModel 算式
* @return
*/
@SuppressWarnings("unchecked")
private double account(String numModel){
String operators [] = {"\\+","\\-","\\*","\\/","\\(","\\)"};
for(String operator : operators){
numModel = numModel.replaceAll(operator," "+operator+" ");
}
Stack operStack = new Stack();
String numModels[] = numModel.split("\\s+");
String preEle = "";
for(int i = 0; i < numModels.length; i++){
if(isExpression(numModels[i])){
if(preEle == null || preEle.equals("")){
preEle = numModels[i];
} else {
if(priority(preEle) >= priority(numModels[i])){
double d1 = Double.parseDouble(String.valueOf(operStack.pop()));
double d2 = Double.parseDouble(String.valueOf(operStack.pop()));
operStack.push(operation(d2,d1,preEle));
preEle = numModels[i];
} else if(priority(preEle) < priority(numModels[i])){
double d1 = Double.parseDouble(String.valueOf(operStack.pop()));
double d2 = Double.parseDouble(numModels[i+1]);
operStack.push(operation(d1,d2,numModels[i]));
i++;
}
}
} else {
operStack.push(numModels[i]);
}
}
double d1 = Double.parseDouble(String.valueOf(operStack.pop()));
double d2 = Double.parseDouble(String.valueOf(operStack.pop()));
return operation(d2,d1,preEle);
}
/**
* @param args
*/
public static void main(String[] args) {
String numModel = "111.1 * (2 - 1) + (2 - 1) + 50 - 10 * (12 + 3)";
System.out.println(new Arithmetic().doAccount(numModel));
}
}
小弟也是一菜鸟，如果有什么不对的地方，还请大家多多指出来！
