java計算數學表達式

 
import java.util.EmptyStackException;
import java.util.Stack;

public class CaculateFunction {
    private static String[] TrnsInToSufix(String IFX)// PFX放后綴表達式，IFX為中綴表達式
    {
        String PFX[] = new String[IFX.length()];
        StringBuffer numBuffer = new StringBuffer();// 用來保存一個數的
        Stack<String> s = new Stack<String>();// 放操作符
        String a;
        s.push("=");// 第一個為等號
        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 == '.')// 拼數
                {
                    numBuffer.append(ch); // 追加字符
                    ch = IFX.charAt(++i);
                }
                PFX[j++] = numBuffer.toString();// break;
                numBuffer = new StringBuffer(); // 清空已獲取的運算數字
                continue; // 這里要重新循環，因為i已經增加過了
            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() == "√")
                    // 優先級比較，與棧頂比較，
                    PFX[j++] = s.pop();// 當前操作符優先級大于等于棧頂的彈出棧頂
                a = String.valueOf(ch);
                s.push(a);
                break;
            case 's':
            case 'c':
            case 't':// 三角函數
                while (s.size() > 1
                        && (s.peek() == "s" || s.peek() == "c"
                                || s.peek() == "t" || s.peek() == "^" || s
                                .peek() == "√"))
                    // 優先級比較，與棧頂，大于等于的彈出
                    PFX[j++] = s.pop();
                a = String.valueOf(ch);
                s.push(a);
                break;
            case '^':// 冪
            case '√':// 開方
                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)// 后綴表達式求值
{
    String PFX[] = null;
    try {
        PFX = TrnsInToSufix(IFX);
    } catch (EmptyStackException e) {
        return "syntax error";
    }
    int i = 0;
    double x1, x2, n;
    String str;
    Stack<String> s = new Stack<String>();
    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;// 開方
        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 = "));
}

}
</pre>