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PlantUML is a component that allows to quickly write diagrams from text.
There is a newer version: 1.2024.8
// THIS FILE HAS BEEN GENERATED BY A PREPROCESSOR.
/* +=======================================================================
 * |
 * |      PlantUML : a free UML diagram generator
 * |
 * +=======================================================================
 *
 * (C) Copyright 2009-2024, Arnaud Roques
 *
 * Project Info:  https://plantuml.com
 *
 * If you like this project or if you find it useful, you can support us at:
 *
 * https://plantuml.com/patreon (only 1$ per month!)
 * https://plantuml.com/liberapay (only 1€ per month!)
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 *
 *
 * PlantUML is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License V2.
 *
 * THE ACCOMPANYING PROGRAM IS PROVIDED UNDER THE TERMS OF THIS ECLIPSE PUBLIC
 * LICENSE ("AGREEMENT"). [GNU General Public License V2]
 *
 * ANY USE, REPRODUCTION OR DISTRIBUTION OF THE PROGRAM CONSTITUTES
 * RECIPIENT'S ACCEPTANCE OF THIS AGREEMENT.
 *
 * You may obtain a copy of the License at
 *
 * https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * PlantUML can occasionally display sponsored or advertising messages. Those
 * messages are usually generated on welcome or error images and never on
 * functional diagrams.
 * See https://plantuml.com/professional if you want to remove them
 *
 * Images (whatever their format : PNG, SVG, EPS...) generated by running PlantUML
 * are owned by the author of their corresponding sources code (that is, their
 * textual description in PlantUML language). Those images are not covered by
 * this GPL v2 license.
 *
 * The generated images can then be used without any reference to the GPL v2 license.
 * It is not even necessary to stipulate that they have been generated with PlantUML,
 * although this will be appreciated by the PlantUML team.
 *
 * There is an exception : if the textual description in PlantUML language is also covered
 * by any license, then the generated images are logically covered
 * by the very same license.
 *
 * This is the IGY distribution (Install GraphViz by Yourself).
 * You have to install GraphViz and to setup the GRAPHVIZ_DOT environment variable
 * (see https://plantuml.com/graphviz-dot )
 *
 * Icons provided by OpenIconic :  https://useiconic.com/open
 * Archimate sprites provided by Archi :  http://www.archimatetool.com
 * Stdlib AWS provided by https://github.com/milo-minderbinder/AWS-PlantUML
 * Stdlib Icons provided https://github.com/tupadr3/plantuml-icon-font-sprites
 * ASCIIMathML (c) Peter Jipsen http://www.chapman.edu/~jipsen
 * ASCIIMathML (c) David Lippman http://www.pierce.ctc.edu/dlippman
 * CafeUndZopfli ported by Eugene Klyuchnikov https://github.com/eustas/CafeUndZopfli
 * Brotli (c) by the Brotli Authors https://github.com/google/brotli
 * Themes (c) by Brett Schwarz https://github.com/bschwarz/puml-themes
 * Twemoji (c) by Twitter at https://twemoji.twitter.com/
 *
 */
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());
	}
}