001 /*
002 * Java Genetic Algorithm Library (jenetics-2.0.2).
003 * Copyright (c) 2007-2014 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 *
017 * Author:
018 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmx.at)
019 */
020 package org.jenetics.util;
021
022 import static java.lang.String.format;
023 import static java.util.Objects.requireNonNull;
024
025 import java.io.Serializable;
026 import java.util.Objects;
027
028 /**
029 * This class contains some short general purpose functions.
030 *
031 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
032 * @since 1.0
033 * @version 2.0 — <em>$Date: 2014-03-31 $</em>
034 */
035 public final class functions extends StaticObject {
036 private functions() {}
037
038 /**
039 * Convert an object to a string by calling the objects {@link Object#toString()}
040 * method.
041 */
042 public static final Function<Object, String>
043 ObjectToString = new Function<Object, String>() {
044 @Override public String apply(final Object value) {
045 return Objects.toString(value);
046 }
047 };
048
049 /**
050 * Convert a string value to its length.
051 */
052 public static final Function<String, Integer>
053 StringLength = new Function<String, Integer>() {
054 @Override public Integer apply(final String value) {
055 return value.length();
056 }
057 };
058
059 /**
060 * Convert a string to an integer. If the string can't be converted, an
061 * {@link NumberFormatException} is throws by the {@link Function#apply(Object)}
062 * method.
063 */
064 public static final Function<String, Integer>
065 StringToInteger = new Function<String, Integer>() {
066 @Override public Integer apply(final String value) {
067 return Integer.parseInt(value);
068 }
069 };
070
071 /**
072 * Convert a string to a long. If the string can't be converted, an
073 * {@link NumberFormatException} is throws by the {@link Function#apply(Object)}
074 * method.
075 */
076 public static final Function<String, Long>
077 StringToLong = new Function<String, Long>() {
078 @Override public Long apply(final String value) {
079 return Long.parseLong(value);
080 }
081 };
082
083 /**
084 * Convert a string to a float. If the string can't be converted, an
085 * {@link NumberFormatException} is throws by the {@link Function#apply(Object)}
086 * method.
087 */
088 public static final Function<String, Float>
089 StringToFloat = new Function<String, Float>() {
090 @Override public Float apply(final String value) {
091 return Float.parseFloat(value);
092 }
093 };
094
095 /**
096 * Convert a string to a double. If the string can't be converted, an
097 * {@link NumberFormatException} is throws by the {@link Function#apply(Object)}
098 * method.
099 */
100 public static final Function<String, Double>
101 StringToDouble = new Function<String, Double>() {
102 @Override public Double apply(final String value) {
103 return Double.parseDouble(value);
104 }
105 };
106
107
108 /**
109 * A predicate which return {@code true} if an given value is {@code null}.
110 */
111 public static final Function<Object, Boolean>
112 Null = new Function<Object, Boolean>() {
113 @Override public Boolean apply(final Object object) {
114 return object == null ? Boolean.TRUE : Boolean.FALSE;
115 }
116 @Override public String toString() {
117 return format("%s", getClass().getSimpleName());
118 }
119 };
120
121 /**
122 * Return a predicate which negates the return value of the given predicate.
123 *
124 * @param <T> the value type to check.
125 * @param a the predicate to negate.
126 * @return a predicate which negates the return value of the given predicate.
127 * @throws NullPointerException if the given predicate is {@code null}.
128 */
129 public static <T> Function<T, Boolean> not(final Function<? super T, Boolean> a) {
130 requireNonNull(a);
131 return new Function<T, Boolean>() {
132 @Override public Boolean apply(final T object) {
133 return a.apply(object) ? Boolean.FALSE : Boolean.TRUE;
134 }
135 @Override public String toString() {
136 return format("%s[%s]", getClass().getSimpleName(), a);
137 }
138 };
139 }
140
141 /**
142 * Return a {@code and} combination of the given predicates.
143 *
144 * @param <T> the value type to check.
145 * @param a the first predicate
146 * @param b the second predicate
147 * @return a {@code and} combination of the given predicates.
148 * @throws NullPointerException if one of the given predicates is
149 * {@code null}.
150 */
151 public static <T> Function<T, Boolean> and(
152 final Function<? super T, Boolean> a,
153 final Function<? super T, Boolean> b
154 ) {
155 requireNonNull(a);
156 requireNonNull(b);
157 return new Function<T, Boolean>() {
158 @Override public Boolean apply(final T object) {
159 return a.apply(object) && b.apply(object);
160 }
161 @Override public String toString() {
162 return format("%s[%s, %s]", getClass().getSimpleName(), a, b);
163 }
164 };
165 }
166
167 /**
168 * Return a {@code or} combination of the given predicates.
169 *
170 * @param <T> the value type to check.
171 * @param a the first predicate
172 * @param b the second predicate
173 * @return a {@code and} combination of the given predicates.
174 * @throws NullPointerException if one of the given predicates is
175 * {@code null}.
176 */
177 public static <T> Function<T, Boolean> or(
178 final Function<? super T, Boolean> a,
179 final Function<? super T, Boolean> b
180 ) {
181 requireNonNull(a);
182 requireNonNull(b);
183 return new Function<T, Boolean>() {
184 @Override public Boolean apply(final T object) {
185 return a.apply(object) || b.apply(object);
186 }
187 @Override public String toString() {
188 return format(
189 "%s[%s, %s]",
190 getClass().getSimpleName(), a, b
191 );
192 }
193 };
194 }
195
196
197 private static final class Identity
198 implements Function<Object, Object>, Serializable
199 {
200 private static final long serialVersionUID = 1L;
201
202 @Override
203 public Object apply(final Object value) {
204 return value;
205 }
206 }
207
208 private static Function<Object, Object> IDENTITY = new Identity();
209
210 /**
211 * Return the identity function for the given type.
212 *
213 * @param <T> the parameter type for the identity function
214 * @return the identity function for the given type.
215 */
216 @SuppressWarnings("unchecked")
217 public static <T> Function<T, T> Identity() {
218 return (Function<T, T>)IDENTITY;
219 }
220
221
222 public static <A, B, C> Function<A, C> compose(
223 final Function<A, B> f1,
224 final Function<B, C> f2
225 ) {
226 requireNonNull(f1, "Function 1");
227 requireNonNull(f2, "Function 2");
228
229 return new Function<A, C>() {
230 @Override public C apply(A value) {
231 return f2.apply(f1.apply(value));
232 }
233 };
234 }
235
236 public static <A, B, C, D> Function<A, D> compose(
237 final Function<A, B> f1,
238 final Function<B, C> f2,
239 final Function<C, D> f3
240 ) {
241 return compose(compose(f1, f2), f3);
242 }
243
244 public static <A, B, C, D, E> Function<A, E> compose(
245 final Function<A, B> f1,
246 final Function<B, C> f2,
247 final Function<C, D> f3,
248 final Function<D, E> f4
249 ) {
250 return compose(compose(compose(f1, f2), f3), f4);
251 }
252
253 public static <A, B, C, D, E, F> Function<A, F> compose(
254 final Function<A, B> f1,
255 final Function<B, C> f2,
256 final Function<C, D> f3,
257 final Function<D, E> f4,
258 final Function<E, F> f5
259 ) {
260 return compose(compose(compose(compose(f1, f2), f3), f4), f5);
261 }
262
263 }
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