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EvalEx is a handy expression evaluator for Java, that allows to evaluate simple mathematical and boolean expressions.

There is a newer version: 2.7

/*
 * Copyright 2018 Udo Klimaschewski
 * 
 * http://UdoJava.com/
 * http://about.me/udo.klimaschewski
 * 
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 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.
 * 
 */
package com.udojava.evalex;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

import com.udojava.evalex.Expression.LazyNumber;

/**
 * Abstract implementation of a direct function.

 * 

 * This abstract implementation does implement lazyEval so that it returns
 * the result of eval.
 */
public abstract class AbstractFunction extends AbstractLazyFunction implements Function {

	/**
	 * Creates a new function with given name and parameter count.
	 *
	 * @param name
	 *            The name of the function.
	 * @param numParams
	 *            The number of parameters for this function.
	 *            -1 denotes a variable number of parameters.
	 */
	protected AbstractFunction(String name, int numParams) {
		super(name, numParams);
	}

	/**
	 * Creates a new function with given name and parameter count.
	 *
	 * @param name
	 *            The name of the function.
	 * @param numParams
	 *            The number of parameters for this function.
	 *            -1 denotes a variable number of parameters.
	 * @param booleanFunction
	 *            Whether this function is a boolean function.
	 */
	protected AbstractFunction(String name, int numParams, boolean booleanFunction) {
		super(name, numParams, booleanFunction);
	}

	public LazyNumber lazyEval(final List lazyParams) {
		return new LazyNumber() {

			private List params;

			public BigDecimal eval() {
				return AbstractFunction.this.eval(getParams());
			}

			public String getString() {
				return String.valueOf(AbstractFunction.this.eval(getParams()));
			}

			private List getParams() {
				if (params == null) {
					params = new ArrayList();
					for (LazyNumber lazyParam : lazyParams) {
						params.add(lazyParam.eval());
					}
				}
				return params;
			}
		};
	}
}