001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. 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 package org.apache.commons.lang;
018
019 import java.io.Serializable;
020 import java.lang.reflect.Array;
021 import java.lang.reflect.InvocationTargetException;
022
023 import org.apache.commons.lang.exception.CloneFailedException;
024 import org.apache.commons.lang.reflect.MethodUtils;
025
026 /**
027 * <p>Operations on <code>Object</code>.</p>
028 *
029 * <p>This class tries to handle <code>null</code> input gracefully.
030 * An exception will generally not be thrown for a <code>null</code> input.
031 * Each method documents its behaviour in more detail.</p>
032 *
033 * <p>#ThreadSafe#</p>
034 * @author Apache Software Foundation
035 * @author <a href="mailto:nissim@nksystems.com">Nissim Karpenstein</a>
036 * @author <a href="mailto:janekdb@yahoo.co.uk">Janek Bogucki</a>
037 * @author Daniel L. Rall
038 * @author Gary Gregory
039 * @author Mario Winterer
040 * @author <a href="mailto:david@davidkarlsen.com">David J. M. Karlsen</a>
041 * @since 1.0
042 * @version $Id: ObjectUtils.java 1057434 2011-01-11 01:27:37Z niallp $
043 */
044 //@Immutable
045 public class ObjectUtils {
046
047 /**
048 * <p>Singleton used as a <code>null</code> placeholder where
049 * <code>null</code> has another meaning.</p>
050 *
051 * <p>For example, in a <code>HashMap</code> the
052 * {@link java.util.HashMap#get(java.lang.Object)} method returns
053 * <code>null</code> if the <code>Map</code> contains
054 * <code>null</code> or if there is no matching key. The
055 * <code>Null</code> placeholder can be used to distinguish between
056 * these two cases.</p>
057 *
058 * <p>Another example is <code>Hashtable</code>, where <code>null</code>
059 * cannot be stored.</p>
060 *
061 * <p>This instance is Serializable.</p>
062 */
063 public static final Null NULL = new Null();
064
065 /**
066 * <p><code>ObjectUtils</code> instances should NOT be constructed in
067 * standard programming. Instead, the class should be used as
068 * <code>ObjectUtils.defaultIfNull("a","b");</code>.</p>
069 *
070 * <p>This constructor is public to permit tools that require a JavaBean instance
071 * to operate.</p>
072 */
073 public ObjectUtils() {
074 super();
075 }
076
077 // Defaulting
078 //-----------------------------------------------------------------------
079 /**
080 * <p>Returns a default value if the object passed is
081 * <code>null</code>.</p>
082 *
083 * <pre>
084 * ObjectUtils.defaultIfNull(null, null) = null
085 * ObjectUtils.defaultIfNull(null, "") = ""
086 * ObjectUtils.defaultIfNull(null, "zz") = "zz"
087 * ObjectUtils.defaultIfNull("abc", *) = "abc"
088 * ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE
089 * </pre>
090 *
091 * @param object the <code>Object</code> to test, may be <code>null</code>
092 * @param defaultValue the default value to return, may be <code>null</code>
093 * @return <code>object</code> if it is not <code>null</code>, defaultValue otherwise
094 */
095 public static Object defaultIfNull(Object object, Object defaultValue) {
096 return object != null ? object : defaultValue;
097 }
098
099 /**
100 * <p>Compares two objects for equality, where either one or both
101 * objects may be <code>null</code>.</p>
102 *
103 * <pre>
104 * ObjectUtils.equals(null, null) = true
105 * ObjectUtils.equals(null, "") = false
106 * ObjectUtils.equals("", null) = false
107 * ObjectUtils.equals("", "") = true
108 * ObjectUtils.equals(Boolean.TRUE, null) = false
109 * ObjectUtils.equals(Boolean.TRUE, "true") = false
110 * ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE) = true
111 * ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
112 * </pre>
113 *
114 * @param object1 the first object, may be <code>null</code>
115 * @param object2 the second object, may be <code>null</code>
116 * @return <code>true</code> if the values of both objects are the same
117 */
118 public static boolean equals(Object object1, Object object2) {
119 if (object1 == object2) {
120 return true;
121 }
122 if ((object1 == null) || (object2 == null)) {
123 return false;
124 }
125 return object1.equals(object2);
126 }
127
128 /**
129 * <p>Compares two objects for inequality, where either one or both
130 * objects may be <code>null</code>.</p>
131 *
132 * <pre>
133 * ObjectUtils.notEqual(null, null) = false
134 * ObjectUtils.notEqual(null, "") = true
135 * ObjectUtils.notEqual("", null) = true
136 * ObjectUtils.notEqual("", "") = false
137 * ObjectUtils.notEqual(Boolean.TRUE, null) = true
138 * ObjectUtils.notEqual(Boolean.TRUE, "true") = true
139 * ObjectUtils.notEqual(Boolean.TRUE, Boolean.TRUE) = false
140 * ObjectUtils.notEqual(Boolean.TRUE, Boolean.FALSE) = true
141 * </pre>
142 *
143 * @param object1 the first object, may be <code>null</code>
144 * @param object2 the second object, may be <code>null</code>
145 * @return <code>false</code> if the values of both objects are the same
146 * @since 2.6
147 */
148 public static boolean notEqual(Object object1, Object object2) {
149 return ObjectUtils.equals(object1, object2) == false;
150 }
151
152 /**
153 * <p>Gets the hash code of an object returning zero when the
154 * object is <code>null</code>.</p>
155 *
156 * <pre>
157 * ObjectUtils.hashCode(null) = 0
158 * ObjectUtils.hashCode(obj) = obj.hashCode()
159 * </pre>
160 *
161 * @param obj the object to obtain the hash code of, may be <code>null</code>
162 * @return the hash code of the object, or zero if null
163 * @since 2.1
164 */
165 public static int hashCode(Object obj) {
166 return (obj == null) ? 0 : obj.hashCode();
167 }
168
169 // Identity ToString
170 //-----------------------------------------------------------------------
171 /**
172 * <p>Gets the toString that would be produced by <code>Object</code>
173 * if a class did not override toString itself. <code>null</code>
174 * will return <code>null</code>.</p>
175 *
176 * <pre>
177 * ObjectUtils.identityToString(null) = null
178 * ObjectUtils.identityToString("") = "java.lang.String@1e23"
179 * ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"
180 * </pre>
181 *
182 * @param object the object to create a toString for, may be
183 * <code>null</code>
184 * @return the default toString text, or <code>null</code> if
185 * <code>null</code> passed in
186 */
187 public static String identityToString(Object object) {
188 if (object == null) {
189 return null;
190 }
191 StringBuffer buffer = new StringBuffer();
192 identityToString(buffer, object);
193 return buffer.toString();
194 }
195
196 /**
197 * <p>Appends the toString that would be produced by <code>Object</code>
198 * if a class did not override toString itself. <code>null</code>
199 * will throw a NullPointerException for either of the two parameters. </p>
200 *
201 * <pre>
202 * ObjectUtils.identityToString(buf, "") = buf.append("java.lang.String@1e23"
203 * ObjectUtils.identityToString(buf, Boolean.TRUE) = buf.append("java.lang.Boolean@7fa"
204 * ObjectUtils.identityToString(buf, Boolean.TRUE) = buf.append("java.lang.Boolean@7fa")
205 * </pre>
206 *
207 * @param buffer the buffer to append to
208 * @param object the object to create a toString for
209 * @since 2.4
210 */
211 public static void identityToString(StringBuffer buffer, Object object) {
212 if (object == null) {
213 throw new NullPointerException("Cannot get the toString of a null identity");
214 }
215 buffer.append(object.getClass().getName())
216 .append('@')
217 .append(Integer.toHexString(System.identityHashCode(object)));
218 }
219
220 /**
221 * <p>Appends the toString that would be produced by <code>Object</code>
222 * if a class did not override toString itself. <code>null</code>
223 * will return <code>null</code>.</p>
224 *
225 * <pre>
226 * ObjectUtils.appendIdentityToString(*, null) = null
227 * ObjectUtils.appendIdentityToString(null, "") = "java.lang.String@1e23"
228 * ObjectUtils.appendIdentityToString(null, Boolean.TRUE) = "java.lang.Boolean@7fa"
229 * ObjectUtils.appendIdentityToString(buf, Boolean.TRUE) = buf.append("java.lang.Boolean@7fa")
230 * </pre>
231 *
232 * @param buffer the buffer to append to, may be <code>null</code>
233 * @param object the object to create a toString for, may be <code>null</code>
234 * @return the default toString text, or <code>null</code> if
235 * <code>null</code> passed in
236 * @since 2.0
237 * @deprecated The design of this method is bad - see LANG-360. Instead, use identityToString(StringBuffer, Object).
238 */
239 public static StringBuffer appendIdentityToString(StringBuffer buffer, Object object) {
240 if (object == null) {
241 return null;
242 }
243 if (buffer == null) {
244 buffer = new StringBuffer();
245 }
246 return buffer
247 .append(object.getClass().getName())
248 .append('@')
249 .append(Integer.toHexString(System.identityHashCode(object)));
250 }
251
252 // ToString
253 //-----------------------------------------------------------------------
254 /**
255 * <p>Gets the <code>toString</code> of an <code>Object</code> returning
256 * an empty string ("") if <code>null</code> input.</p>
257 *
258 * <pre>
259 * ObjectUtils.toString(null) = ""
260 * ObjectUtils.toString("") = ""
261 * ObjectUtils.toString("bat") = "bat"
262 * ObjectUtils.toString(Boolean.TRUE) = "true"
263 * </pre>
264 *
265 * @see StringUtils#defaultString(String)
266 * @see String#valueOf(Object)
267 * @param obj the Object to <code>toString</code>, may be null
268 * @return the passed in Object's toString, or nullStr if <code>null</code> input
269 * @since 2.0
270 */
271 public static String toString(Object obj) {
272 return obj == null ? "" : obj.toString();
273 }
274
275 /**
276 * <p>Gets the <code>toString</code> of an <code>Object</code> returning
277 * a specified text if <code>null</code> input.</p>
278 *
279 * <pre>
280 * ObjectUtils.toString(null, null) = null
281 * ObjectUtils.toString(null, "null") = "null"
282 * ObjectUtils.toString("", "null") = ""
283 * ObjectUtils.toString("bat", "null") = "bat"
284 * ObjectUtils.toString(Boolean.TRUE, "null") = "true"
285 * </pre>
286 *
287 * @see StringUtils#defaultString(String,String)
288 * @see String#valueOf(Object)
289 * @param obj the Object to <code>toString</code>, may be null
290 * @param nullStr the String to return if <code>null</code> input, may be null
291 * @return the passed in Object's toString, or nullStr if <code>null</code> input
292 * @since 2.0
293 */
294 public static String toString(Object obj, String nullStr) {
295 return obj == null ? nullStr : obj.toString();
296 }
297
298 // Min/Max
299 //-----------------------------------------------------------------------
300 /**
301 * Null safe comparison of Comparables.
302 *
303 * @param c1 the first comparable, may be null
304 * @param c2 the second comparable, may be null
305 * @return
306 * <ul>
307 * <li>If both objects are non-null and unequal, the lesser object.
308 * <li>If both objects are non-null and equal, c1.
309 * <li>If one of the comparables is null, the non-null object.
310 * <li>If both the comparables are null, null is returned.
311 * </ul>
312 */
313 public static Object min(Comparable c1, Comparable c2) {
314 return (compare(c1, c2, true) <= 0 ? c1 : c2);
315 }
316
317 /**
318 * Null safe comparison of Comparables.
319 *
320 * @param c1 the first comparable, may be null
321 * @param c2 the second comparable, may be null
322 * @return
323 * <ul>
324 * <li>If both objects are non-null and unequal, the greater object.
325 * <li>If both objects are non-null and equal, c1.
326 * <li>If one of the comparables is null, the non-null object.
327 * <li>If both the comparables are null, null is returned.
328 * </ul>
329 */
330 public static Object max(Comparable c1, Comparable c2) {
331 return (compare(c1, c2, false) >= 0 ? c1 : c2);
332 }
333
334 /**
335 * Null safe comparison of Comparables.
336 * {@code null} is assumed to be less than a non-{@code null} value.
337 *
338 * @param c1 the first comparable, may be null
339 * @param c2 the second comparable, may be null
340 * @return a negative value if c1 < c2, zero if c1 = c2
341 * and a positive value if c1 > c2
342 * @since 2.6
343 */
344 public static int compare(Comparable c1, Comparable c2) {
345 return compare(c1, c2, false);
346 }
347
348 /**
349 * Null safe comparison of Comparables.
350 *
351 * @param c1 the first comparable, may be null
352 * @param c2 the second comparable, may be null
353 * @param nullGreater if true <code>null</code> is considered greater
354 * than a Non-<code>null</code> value or if false <code>null</code> is
355 * considered less than a Non-<code>null</code> value
356 * @return a negative value if c1 < c2, zero if c1 = c2
357 * and a positive value if c1 > c2
358 * @see java.util.Comparator#compare(Object, Object)
359 * @since 2.6
360 */
361 public static int compare(Comparable c1, Comparable c2, boolean nullGreater) {
362 if (c1 == c2) {
363 return 0;
364 } else if (c1 == null) {
365 return (nullGreater ? 1 : -1);
366 } else if (c2 == null) {
367 return (nullGreater ? -1 : 1);
368 }
369 return c1.compareTo(c2);
370 }
371
372 /**
373 * Clone an object.
374 *
375 * @param o the object to clone
376 * @return the clone if the object implements {@link Cloneable} otherwise <code>null</code>
377 * @throws CloneFailedException if the object is cloneable and the clone operation fails
378 * @since 2.6
379 */
380 public static Object clone(final Object o) {
381 if (o instanceof Cloneable) {
382 final Object result;
383 if (o.getClass().isArray()) {
384 final Class componentType = o.getClass().getComponentType();
385 if (!componentType.isPrimitive()) {
386 result = ((Object[])o).clone();
387 } else {
388 int length = Array.getLength(o);
389 result = Array.newInstance(componentType, length);
390 while (length-- > 0) {
391 Array.set(result, length, Array.get(o, length));
392 }
393 }
394 } else {
395 try {
396 result = MethodUtils.invokeMethod(o, "clone", null);
397 } catch (final NoSuchMethodException e) {
398 throw new CloneFailedException("Cloneable type "
399 + o.getClass().getName()
400 + " has no clone method", e);
401 } catch (final IllegalAccessException e) {
402 throw new CloneFailedException("Cannot clone Cloneable type "
403 + o.getClass().getName(), e);
404 } catch (final InvocationTargetException e) {
405 throw new CloneFailedException("Exception cloning Cloneable type "
406 + o.getClass().getName(), e.getTargetException());
407 }
408 }
409 return result;
410 }
411
412 return null;
413 }
414
415 /**
416 * Clone an object if possible. This method is similar to {@link #clone(Object)}, but will
417 * return the provided instance as the return value instead of <code>null</code> if the instance
418 * is not cloneable. This is more convenient if the caller uses different
419 * implementations (e.g. of a service) and some of the implementations do not allow concurrent
420 * processing or have state. In such cases the implementation can simply provide a proper
421 * clone implementation and the caller's code does not have to change.
422 *
423 * @param o the object to clone
424 * @return the clone if the object implements {@link Cloneable} otherwise the object itself
425 * @throws CloneFailedException if the object is cloneable and the clone operation fails
426 * @since 2.6
427 */
428 public static Object cloneIfPossible(final Object o) {
429 final Object clone = clone(o);
430 return clone == null ? o : clone;
431 }
432
433 // Null
434 //-----------------------------------------------------------------------
435 /**
436 * <p>Class used as a null placeholder where <code>null</code>
437 * has another meaning.</p>
438 *
439 * <p>For example, in a <code>HashMap</code> the
440 * {@link java.util.HashMap#get(java.lang.Object)} method returns
441 * <code>null</code> if the <code>Map</code> contains
442 * <code>null</code> or if there is no matching key. The
443 * <code>Null</code> placeholder can be used to distinguish between
444 * these two cases.</p>
445 *
446 * <p>Another example is <code>Hashtable</code>, where <code>null</code>
447 * cannot be stored.</p>
448 */
449 public static class Null implements Serializable {
450 /**
451 * Required for serialization support. Declare serialization compatibility with Commons Lang 1.0
452 *
453 * @see java.io.Serializable
454 */
455 private static final long serialVersionUID = 7092611880189329093L;
456
457 /**
458 * Restricted constructor - singleton.
459 */
460 Null() {
461 super();
462 }
463
464 /**
465 * <p>Ensure singleton.</p>
466 *
467 * @return the singleton value
468 */
469 private Object readResolve() {
470 return ObjectUtils.NULL;
471 }
472 }
473
474 }