evaluateur d 27expressions maths java

1public static double eval(final String str) {
2    return new Object() {
3        int pos = -1, ch;
4
5        void nextChar() {
6            ch = (++pos < str.length()) ? str.charAt(pos) : -1;
7        }
8
9        boolean eat(int charToEat) {
10            while (ch == ' ') nextChar();
11            if (ch == charToEat) {
12                nextChar();
13                return true;
14            }
15            return false;
16        }
17
18        double parse() {
19            nextChar();
20            double x = parseExpression();
21            if (pos < str.length()) throw new RuntimeException("Unexpected: " + (char)ch);
22            return x;
23        }
24
25        // Grammar:
26        // expression = term | expression `+` term | expression `-` term
27        // term = factor | term `*` factor | term `/` factor
28        // factor = `+` factor | `-` factor | `(` expression `)`
29        //        | number | functionName factor | factor `^` factor
30
31        double parseExpression() {
32            double x = parseTerm();
33            for (;;) {
34                if      (eat('+')) x += parseTerm(); // addition
35                else if (eat('-')) x -= parseTerm(); // subtraction
36                else return x;
37            }
38        }
39
40        double parseTerm() {
41            double x = parseFactor();
42            for (;;) {
43                if      (eat('*')) x *= parseFactor(); // multiplication
44                else if (eat('/')) x /= parseFactor(); // division
45                else return x;
46            }
47        }
48
49        double parseFactor() {
50            if (eat('+')) return parseFactor(); // unary plus
51            if (eat('-')) return -parseFactor(); // unary minus
52
53            double x;
54            int startPos = this.pos;
55            if (eat('(')) { // parentheses
56                x = parseExpression();
57                eat(')');
58            } else if ((ch >= '0' && ch <= '9') || ch == '.') { // numbers
59                while ((ch >= '0' && ch <= '9') || ch == '.') nextChar();
60                x = Double.parseDouble(str.substring(startPos, this.pos));
61            } else if (ch >= 'a' && ch <= 'z') { // functions
62                while (ch >= 'a' && ch <= 'z') nextChar();
63                String func = str.substring(startPos, this.pos);
64                x = parseFactor();
65                if (func.equals("sqrt")) x = Math.sqrt(x);
66                else if (func.equals("sin")) x = Math.sin(Math.toRadians(x));
67                else if (func.equals("cos")) x = Math.cos(Math.toRadians(x));
68                else if (func.equals("tan")) x = Math.tan(Math.toRadians(x));
69                else throw new RuntimeException("Unknown function: " + func);
70            } else {
71                throw new RuntimeException("Unexpected: " + (char)ch);
72            }
73
74            if (eat('^')) x = Math.pow(x, parseFactor()); // exponentiation
75
76            return x;
77        }
78    }.parse();
79}
80