import java.util.EmptyStackException;
import java.util.Stack;
public class CaculateFunction {
private static String[] TrnsInToSufix(String IFX)// PFX放后缀表达式，IFX为中缀表达式
{
String PFX[] = new String[IFX.length()];
StringBuffer numBuffer = new StringBuffer();// 用来保存一个数的
Stack s = new Stack();// 放操作符
String a;
s.push("=");// 第一个为等号
int i = 0, j = 0;
char ch;
for (i = 0; i < IFX.length();) {
ch = IFX.charAt(i);
switch (ch) {
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
while (Character.isDigit(ch) || ch == '.')// 拼数
{
numBuffer.append(ch); // 追加字符
ch = IFX.charAt(++i);
}
PFX[j++] = numBuffer.toString();// break;
numBuffer = new StringBuffer(); // 清空已获取的运算数字
continue; // 这里要重新循环，因为i已经增加过了
case '(':
s.push("(");
break;
case ')':
while (s.peek() != "(")
PFX[j++] = s.pop();
break;
case '+':
case '-':
while (s.size() > 1 && s.peek() != "(")
PFX[j++] = s.pop();
a = String.valueOf(ch);
s.push(a);
break;
case '*':
case '/':
while (s.size() > 1 && (s.peek() == "*") || s.peek() == "/"
|| s.peek() == "s" || s.peek() == "c"
|| s.peek() == "t" || s.peek() == "^"
|| s.peek() == "√")
// 优先级比较，与栈顶比较，
PFX[j++] = s.pop();// 当前操作符优先级大于等于栈顶的弹出栈顶
a = String.valueOf(ch);
s.push(a);
break;
case 's':
case 'c':
case 't':// 三角函数
while (s.size() > 1
&& (s.peek() == "s" || s.peek() == "c"
|| s.peek() == "t" || s.peek() == "^" || s
.peek() == "√"))
// 优先级比较，与栈顶，大于等于的弹出
PFX[j++] = s.pop();
a = String.valueOf(ch);
s.push(a);
break;
case '^':// 幂
case '√':// 开方
while (s.size() > 1 && (s.peek() == "^" || s.peek() == "√"))
PFX[j++] = s.pop();
a = String.valueOf(ch);
s.push(a);
break;
}
i++;
}
while (s.size() > 1)
PFX[j++] = s.pop();
PFX[j] = "=";
return PFX;
}
public static String Evaluate(String IFX)// 后缀表达式求值
{
String PFX[] = null;
try {
PFX = TrnsInToSufix(IFX);
} catch (EmptyStackException e) {
return "syntax error";
}
int i = 0;
double x1, x2, n;
String str;
Stack s = new Stack();
while (PFX[i] != "=") {
str = PFX[i];
switch (str.charAt(0)) {
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
s.push(str);
break;
case '+':
x1 = Double.parseDouble(s.pop());
x2 = Double.parseDouble(s.pop());
n = x1 + x2;
s.push(String.valueOf(n));
break;
case '-':
x1 = Double.parseDouble(s.pop());
x2 = Double.parseDouble(s.pop());
n = x2 - x1;
s.push(String.valueOf(n));
break;
case '*':
x1 = Double.parseDouble(s.pop());
x2 = Double.parseDouble(s.pop());
n = x1 * x2;
s.push(String.valueOf(n));
break;
case '/':
x1 = Double.parseDouble(s.pop());
x2 = Double.parseDouble(s.pop());
n = x2 / x1;
s.push(String.valueOf(n));
break;
case 's':
x1 = Double.parseDouble(s.pop());
n = Math.sin(x1 * Math.PI / 180);
s.push(String.valueOf(n));
break;
case 'c':
x1 = Double.parseDouble(s.pop());
n = Math.cos(x1 * Math.PI / 180);
s.push(String.valueOf(n));
break;
case 't':
x1 = Double.parseDouble(s.pop());
n = Math.tan(x1 * Math.PI / 180);
s.push(String.valueOf(n));
break;
case '√':
x1 = Double.parseDouble(s.pop());
n = Math.sqrt(x1);
s.push(String.valueOf(n));
break;// 开方
case '^':
x1 = Double.parseDouble(s.pop());
x2 = Double.parseDouble(s.pop());
n = Math.pow(x2, x1);
s.push(String.valueOf(n));
break;
}
i++;
}
String result = s.pop();
return result;
}
public static void main(String args[]) {
System.out.println(Evaluate("(31 + 21) * 51 - (21 + 33) / 2 = "));
}
}
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