112 lines
2.3 KiB
Java
112 lines
2.3 KiB
Java
|
import javax.script.ScriptEngine;
|
||
|
|
import javax.script.ScriptEngineManager;
|
||
|
|
|
||
|
|
public class ExpressionParserRecursiveDescent {
|
||
|
|
|
||
|
|
String s;
|
||
|
|
int pos;
|
||
|
|
char token;
|
||
|
|
double tokval;
|
||
|
|
|
||
|
|
static boolean isDigitOrDot(char x) {
|
||
|
|
return Character.isDigit(x) || x == '.';
|
||
|
|
}
|
||
|
|
|
||
|
|
int next() {
|
||
|
|
while (true) {
|
||
|
|
if (pos == s.length())
|
||
|
|
return token = 255;
|
||
|
|
char c = s.charAt(pos++);
|
||
|
|
if ("+-*/^()\n".indexOf(c) != -1)
|
||
|
|
return token = c;
|
||
|
|
if (Character.isSpaceChar(c))
|
||
|
|
continue;
|
||
|
|
if (Character.isDigit(c) || c == '.') {
|
||
|
|
String operand = "" + c;
|
||
|
|
while (pos < s.length() && isDigitOrDot(s.charAt(pos)))
|
||
|
|
operand += c = s.charAt(pos++);
|
||
|
|
tokval = Double.parseDouble(operand);
|
||
|
|
return token = 'n';
|
||
|
|
}
|
||
|
|
throw new RuntimeException("Bad character: " + c);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
void skip(int ch) {
|
||
|
|
if (token != ch)
|
||
|
|
throw new RuntimeException("Bad character: " + token + ", expected: " + ch);
|
||
|
|
next();
|
||
|
|
}
|
||
|
|
|
||
|
|
// number ::= number | '(' expression ')'
|
||
|
|
double number() {
|
||
|
|
if (token == 'n') {
|
||
|
|
double v = tokval;
|
||
|
|
skip('n');
|
||
|
|
return v;
|
||
|
|
}
|
||
|
|
skip('(');
|
||
|
|
double v = expression();
|
||
|
|
skip(')');
|
||
|
|
return v;
|
||
|
|
}
|
||
|
|
|
||
|
|
// factor ::= number | number '^' factor
|
||
|
|
double factor() {
|
||
|
|
double v = number();
|
||
|
|
if (token == '^') {
|
||
|
|
skip('^');
|
||
|
|
v = Math.pow(v, factor());
|
||
|
|
}
|
||
|
|
return v;
|
||
|
|
}
|
||
|
|
|
||
|
|
// term ::= factor | term '*' factor | term '/' factor
|
||
|
|
double term() {
|
||
|
|
double v = factor();
|
||
|
|
while (true) {
|
||
|
|
if (token == '*') {
|
||
|
|
skip('*');
|
||
|
|
v *= factor();
|
||
|
|
} else if (token == '/') {
|
||
|
|
skip('/');
|
||
|
|
v /= factor();
|
||
|
|
} else
|
||
|
|
return v;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// expression ::= term | expression '+' term | expression '-' term
|
||
|
|
double expression() {
|
||
|
|
double v = term();
|
||
|
|
for (; ; ) {
|
||
|
|
if (token == '+') {
|
||
|
|
skip('+');
|
||
|
|
v += term();
|
||
|
|
} else if (token == '-') {
|
||
|
|
skip('-');
|
||
|
|
v -= term();
|
||
|
|
} else
|
||
|
|
return v;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
public static void main(String[] args) throws Exception {
|
||
|
|
ScriptEngine engine = new ScriptEngineManager().getEngineByName("JavaScript");
|
||
|
|
|
||
|
|
String exp = "1+2*3*4+3*(2+2)-100\n";
|
||
|
|
System.out.println(engine.eval(exp));
|
||
|
|
|
||
|
|
ExpressionParserRecursiveDescent parser = new ExpressionParserRecursiveDescent();
|
||
|
|
parser.s = exp;
|
||
|
|
parser.next();
|
||
|
|
while (parser.token != 255) {
|
||
|
|
if (parser.token == '\n') {
|
||
|
|
parser.skip('\n');
|
||
|
|
continue;
|
||
|
|
}
|
||
|
|
System.out.printf("%.5f", parser.expression());
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|