/*
* Copyright 2014 Frank Asseg
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.
*/
package net.objecthunter.exp4j.function;
/**
* A class representing a Function which can be used in an expression
*/
public abstract class Function {
protected final String name;
protected final int numArguments;
/**
* Create a new Function with a given name and number of arguments
* @param name the name of the Function
* @param numArguments the number of arguments the function takes
*/
public Function(String name, int numArguments) {
if (numArguments < 0) {
throw new IllegalArgumentException("The number of function arguments can not be less than 0 for '" +
name + "'");
}
if (!isValidFunctionName(name)) {
throw new IllegalArgumentException("The function name '" + name +"' is invalid");
}
this.name = name;
this.numArguments = numArguments;
}
/**
* Create a new Function with a given name that takes a single argument
* @param name the name of the Function
*/
public Function(String name) {
this(name, 1);
}
/**
* Get the name of the Function
* @return the name
*/
public String getName() {
return name;
}
/**
* Get the number of arguments for this function
* @return the number of arguments
*/
public int getNumArguments() {
return numArguments;
}
/**
* Method that does the actual calculation of the function value given the arguments
* @param args the set of arguments used for calculating the function
* @return the result of the function evaluation
*/
public abstract double apply(double... args);
/**
* Get the set of characters which are allowed for use in Function names.
* @return the set of characters allowed
*/
public static char[] getAllowedFunctionCharacters() {
char[] chars = new char[53];
int count = 0;
for (int i = 65; i < 91; i++) {
chars[count++] = (char) i;
}
for (int i = 97; i < 123; i++) {
chars[count++] = (char) i;
}
chars[count] = '_';
return chars;
}
public static boolean isValidFunctionName(final String name) {
if (name == null) {
return false;
}
final int size = name.length();
if (size == 0) {
return false;
}
for (int i=0;i< size;i++) {
final char c = name.charAt(i);
if (Character.isLetter(c) || c == '_') {
continue;
} else if (Character.isDigit(c) && i > 0) {
continue;
}
return false;
}
return true;
}
}