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PlantUML is a component that allows to quickly write diagrams from text.
// THIS FILE HAS BEEN GENERATED BY A PREPROCESSOR.
/* +=======================================================================
* |
* | PlantUML : a free UML diagram generator
* |
* +=======================================================================
*
* (C) Copyright 2009-2024, Arnaud Roques
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* Project Info: https://plantuml.com
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* PlantUML is free software; you can redistribute it and/or modify it
* under the terms of the MIT License.
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* See http://opensource.org/licenses/MIT
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* a copy of this software and associated documentation files (the "Software"),
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
* IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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* messages are usually generated on welcome or error images and never on
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*
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* ASCIIMathML (c) Peter Jipsen http://www.chapman.edu/~jipsen
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*/
package net.sourceforge.plantuml.preproc;
// http://stackoverflow.com/questions/3422673/evaluating-a-math-expression-given-in-string-form
public class EvalMath {
private final String str;
private int pos = -1;
private char ch;
public EvalMath(String str) {
this.str = str;
}
private void nextChar() {
pos++;
if (pos < str.length()) {
ch = str.charAt(pos);
} else {
ch = '\0';
}
}
private boolean eat(int charToEat) {
while (ch == ' ') {
nextChar();
}
if (ch == charToEat) {
nextChar();
return true;
}
return false;
}
private double parseExpression() {
double x = parseTerm();
while (true) {
if (eat('+')) {
x += parseTerm();
} else if (eat('-')) {
x -= parseTerm();
} else {
return x;
}
}
}
private double parseTerm() {
double x = parseFactor();
while (true) {
if (eat('*')) {
x *= parseFactor();
} else if (eat('/')) {
x /= parseFactor();
} else {
return x;
}
}
}
private double parseFactor() {
if (eat('+')) {
return parseFactor();
}
if (eat('-')) {
return -parseFactor();
}
final double x;
final int startPos = pos;
if (eat('(')) {
x = parseExpression();
eat(')');
} else if ((ch >= '0' && ch <= '9') || ch == '.') {
while ((ch >= '0' && ch <= '9') || ch == '.')
nextChar();
x = Double.parseDouble(str.substring(startPos, pos));
} else if (ch >= 'a' && ch <= 'z') {
while (ch >= 'a' && ch <= 'z') {
nextChar();
}
final String func = str.substring(startPos, pos);
x = parseFactor();
throw new RuntimeException("Unknown function: " + func);
} else {
throw new RuntimeException("Unexpected: " + (char) ch);
}
return x;
}
public double eval() {
nextChar();
double x = parseExpression();
if (pos < str.length()) {
throw new RuntimeException("Unexpected: " + (char) ch);
}
return x;
}
public static void main(String[] args) {
final EvalMath eval = new EvalMath("33+2*(4+1)");
System.err.println(eval.eval());
}
}