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.lang3;
018    
019    import java.io.Serializable;
020    import java.lang.reflect.Array;
021    import java.lang.reflect.InvocationTargetException;
022    import java.lang.reflect.Method;
023    import java.util.Collections;
024    import java.util.Comparator;
025    import java.util.HashMap;
026    import java.util.Map;
027    import java.util.TreeSet;
028    
029    import org.apache.commons.lang3.exception.CloneFailedException;
030    import org.apache.commons.lang3.mutable.MutableInt;
031    
032    /**
033     * <p>Operations on {@code Object}.</p>
034     *
035     * <p>This class tries to handle {@code null} input gracefully.
036     * An exception will generally not be thrown for a {@code null} input.
037     * Each method documents its behaviour in more detail.</p>
038     *
039     * <p>#ThreadSafe#</p>
040     * @since 1.0
041     * @version $Id: ObjectUtils.java 1199894 2011-11-09 17:53:59Z ggregory $
042     */
043    //@Immutable
044    public class ObjectUtils {
045    
046        /**
047         * <p>Singleton used as a {@code null} placeholder where
048         * {@code null} has another meaning.</p>
049         *
050         * <p>For example, in a {@code HashMap} the
051         * {@link java.util.HashMap#get(java.lang.Object)} method returns
052         * {@code null} if the {@code Map} contains {@code null} or if there
053         * is no matching key. The {@code Null} placeholder can be used to
054         * distinguish between these two cases.</p>
055         *
056         * <p>Another example is {@code Hashtable}, where {@code null}
057         * cannot be stored.</p>
058         *
059         * <p>This instance is Serializable.</p>
060         */
061        public static final Null NULL = new Null();
062    
063        /**
064         * <p>{@code ObjectUtils} instances should NOT be constructed in
065         * standard programming. Instead, the static methods on the class should
066         * be used, such as {@code ObjectUtils.defaultIfNull("a","b");}.</p>
067         *
068         * <p>This constructor is public to permit tools that require a JavaBean
069         * instance to operate.</p>
070         */
071        public ObjectUtils() {
072            super();
073        }
074    
075        // Defaulting
076        //-----------------------------------------------------------------------
077        /**
078         * <p>Returns a default value if the object passed is {@code null}.</p>
079         *
080         * <pre>
081         * ObjectUtils.defaultIfNull(null, null)      = null
082         * ObjectUtils.defaultIfNull(null, "")        = ""
083         * ObjectUtils.defaultIfNull(null, "zz")      = "zz"
084         * ObjectUtils.defaultIfNull("abc", *)        = "abc"
085         * ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE
086         * </pre>
087         *
088         * @param <T> the type of the object
089         * @param object  the {@code Object} to test, may be {@code null}
090         * @param defaultValue  the default value to return, may be {@code null}
091         * @return {@code object} if it is not {@code null}, defaultValue otherwise
092         */
093        public static <T> T defaultIfNull(T object, T defaultValue) {
094            return object != null ? object : defaultValue;
095        }
096    
097        /**
098         * <p>Returns the first value in the array which is not {@code null}.
099         * If all the values are {@code null} or the array is {@code null}
100         * or empty then {@code null} is returned.</p>
101         *
102         * <pre>
103         * ObjectUtils.firstNonNull(null, null)      = null
104         * ObjectUtils.firstNonNull(null, "")        = ""
105         * ObjectUtils.firstNonNull(null, null, "")  = ""
106         * ObjectUtils.firstNonNull(null, "zz")      = "zz"
107         * ObjectUtils.firstNonNull("abc", *)        = "abc"
108         * ObjectUtils.firstNonNull(null, "xyz", *)  = "xyz"
109         * ObjectUtils.firstNonNull(Boolean.TRUE, *) = Boolean.TRUE
110         * ObjectUtils.firstNonNull()                = null
111         * </pre>
112         *
113         * @param <T> the component type of the array
114         * @param values  the values to test, may be {@code null} or empty
115         * @return the first value from {@code values} which is not {@code null},
116         *  or {@code null} if there are no non-null values
117         * @since 3.0
118         */
119        public static <T> T firstNonNull(T... values) {
120            if (values != null) {
121                for (T val : values) {
122                    if (val != null) {
123                        return val;
124                    }
125                }
126            }
127            return null;
128        }
129    
130        // Null-safe equals/hashCode
131        //-----------------------------------------------------------------------
132        /**
133         * <p>Compares two objects for equality, where either one or both
134         * objects may be {@code null}.</p>
135         *
136         * <pre>
137         * ObjectUtils.equals(null, null)                  = true
138         * ObjectUtils.equals(null, "")                    = false
139         * ObjectUtils.equals("", null)                    = false
140         * ObjectUtils.equals("", "")                      = true
141         * ObjectUtils.equals(Boolean.TRUE, null)          = false
142         * ObjectUtils.equals(Boolean.TRUE, "true")        = false
143         * ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE)  = true
144         * ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
145         * </pre>
146         *
147         * @param object1  the first object, may be {@code null}
148         * @param object2  the second object, may be {@code null}
149         * @return {@code true} if the values of both objects are the same
150         */
151        public static boolean equals(Object object1, Object object2) {
152            if (object1 == object2) {
153                return true;
154            }
155            if (object1 == null || object2 == null) {
156                return false;
157            }
158            return object1.equals(object2);
159        }
160    
161        /**
162         * <p>Compares two objects for inequality, where either one or both
163         * objects may be {@code null}.</p>
164         *
165         * <pre>
166         * ObjectUtils.notEqual(null, null)                  = false
167         * ObjectUtils.notEqual(null, "")                    = true
168         * ObjectUtils.notEqual("", null)                    = true
169         * ObjectUtils.notEqual("", "")                      = false
170         * ObjectUtils.notEqual(Boolean.TRUE, null)          = true
171         * ObjectUtils.notEqual(Boolean.TRUE, "true")        = true
172         * ObjectUtils.notEqual(Boolean.TRUE, Boolean.TRUE)  = false
173         * ObjectUtils.notEqual(Boolean.TRUE, Boolean.FALSE) = true
174         * </pre>
175         *
176         * @param object1  the first object, may be {@code null}
177         * @param object2  the second object, may be {@code null}
178         * @return {@code false} if the values of both objects are the same
179         */
180        public static boolean notEqual(Object object1, Object object2) {
181            return ObjectUtils.equals(object1, object2) == false;
182        }
183    
184        /**
185         * <p>Gets the hash code of an object returning zero when the
186         * object is {@code null}.</p>
187         *
188         * <pre>
189         * ObjectUtils.hashCode(null)   = 0
190         * ObjectUtils.hashCode(obj)    = obj.hashCode()
191         * </pre>
192         *
193         * @param obj  the object to obtain the hash code of, may be {@code null}
194         * @return the hash code of the object, or zero if null
195         * @since 2.1
196         */
197        public static int hashCode(Object obj) {
198            // hashCode(Object) retained for performance, as hash code is often critical
199            return obj == null ? 0 : obj.hashCode();
200        }
201    
202        /**
203         * <p>Gets the hash code for multiple objects.</p>
204         * 
205         * <p>This allows a hash code to be rapidly calculated for a number of objects.
206         * The hash code for a single object is the <em>not</em> same as {@link #hashCode(Object)}.
207         * The hash code for multiple objects is the same as that calculated by an
208         * {@code ArrayList} containing the specified objects.</p>
209         *
210         * <pre>
211         * ObjectUtils.hashCodeMulti()                 = 1
212         * ObjectUtils.hashCodeMulti((Object[]) null)  = 1
213         * ObjectUtils.hashCodeMulti(a)                = 31 + a.hashCode()
214         * ObjectUtils.hashCodeMulti(a,b)              = (31 + a.hashCode()) * 31 + b.hashCode()
215         * ObjectUtils.hashCodeMulti(a,b,c)            = ((31 + a.hashCode()) * 31 + b.hashCode()) * 31 + c.hashCode()
216         * </pre>
217         *
218         * @param objects  the objects to obtain the hash code of, may be {@code null}
219         * @return the hash code of the objects, or zero if null
220         * @since 3.0
221         */
222        public static int hashCodeMulti(Object... objects) {
223            int hash = 1;
224            if (objects != null) {
225                for (Object object : objects) {
226                    hash = hash * 31 + ObjectUtils.hashCode(object);
227                }
228            }
229            return hash;
230        }
231    
232        // Identity ToString
233        //-----------------------------------------------------------------------
234        /**
235         * <p>Gets the toString that would be produced by {@code Object}
236         * if a class did not override toString itself. {@code null}
237         * will return {@code null}.</p>
238         *
239         * <pre>
240         * ObjectUtils.identityToString(null)         = null
241         * ObjectUtils.identityToString("")           = "java.lang.String@1e23"
242         * ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"
243         * </pre>
244         *
245         * @param object  the object to create a toString for, may be
246         *  {@code null}
247         * @return the default toString text, or {@code null} if
248         *  {@code null} passed in
249         */
250        public static String identityToString(Object object) {
251            if (object == null) {
252                return null;
253            }
254            StringBuffer buffer = new StringBuffer();
255            identityToString(buffer, object);
256            return buffer.toString();
257        }
258    
259        /**
260         * <p>Appends the toString that would be produced by {@code Object}
261         * if a class did not override toString itself. {@code null}
262         * will throw a NullPointerException for either of the two parameters. </p>
263         *
264         * <pre>
265         * ObjectUtils.identityToString(buf, "")            = buf.append("java.lang.String@1e23"
266         * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa"
267         * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
268         * </pre>
269         *
270         * @param buffer  the buffer to append to
271         * @param object  the object to create a toString for
272         * @since 2.4
273         */
274        public static void identityToString(StringBuffer buffer, Object object) {
275            if (object == null) {
276                throw new NullPointerException("Cannot get the toString of a null identity");
277            }
278            buffer.append(object.getClass().getName())
279                  .append('@')
280                  .append(Integer.toHexString(System.identityHashCode(object)));
281        }
282    
283        // ToString
284        //-----------------------------------------------------------------------
285        /**
286         * <p>Gets the {@code toString} of an {@code Object} returning
287         * an empty string ("") if {@code null} input.</p>
288         *
289         * <pre>
290         * ObjectUtils.toString(null)         = ""
291         * ObjectUtils.toString("")           = ""
292         * ObjectUtils.toString("bat")        = "bat"
293         * ObjectUtils.toString(Boolean.TRUE) = "true"
294         * </pre>
295         *
296         * @see StringUtils#defaultString(String)
297         * @see String#valueOf(Object)
298         * @param obj  the Object to {@code toString}, may be null
299         * @return the passed in Object's toString, or nullStr if {@code null} input
300         * @since 2.0
301         */
302        public static String toString(Object obj) {
303            return obj == null ? "" : obj.toString();
304        }
305    
306        /**
307         * <p>Gets the {@code toString} of an {@code Object} returning
308         * a specified text if {@code null} input.</p>
309         *
310         * <pre>
311         * ObjectUtils.toString(null, null)           = null
312         * ObjectUtils.toString(null, "null")         = "null"
313         * ObjectUtils.toString("", "null")           = ""
314         * ObjectUtils.toString("bat", "null")        = "bat"
315         * ObjectUtils.toString(Boolean.TRUE, "null") = "true"
316         * </pre>
317         *
318         * @see StringUtils#defaultString(String,String)
319         * @see String#valueOf(Object)
320         * @param obj  the Object to {@code toString}, may be null
321         * @param nullStr  the String to return if {@code null} input, may be null
322         * @return the passed in Object's toString, or nullStr if {@code null} input
323         * @since 2.0
324         */
325        public static String toString(Object obj, String nullStr) {
326            return obj == null ? nullStr : obj.toString();
327        }
328    
329        // Comparable
330        //-----------------------------------------------------------------------
331        /**
332         * <p>Null safe comparison of Comparables.</p>
333         *
334         * @param <T> type of the values processed by this method
335         * @param values the set of comparable values, may be null
336         * @return
337         *  <ul>
338         *   <li>If any objects are non-null and unequal, the lesser object.
339         *   <li>If all objects are non-null and equal, the first.
340         *   <li>If any of the comparables are null, the lesser of the non-null objects.
341         *   <li>If all the comparables are null, null is returned.
342         *  </ul>
343         */
344        public static <T extends Comparable<? super T>> T min(T... values) {
345            T result = null;
346            if (values != null) {
347                for (T value : values) {
348                    if (compare(value, result, true) < 0) {
349                        result = value;
350                    }
351                }
352            }
353            return result;
354        }
355    
356        /**
357         * <p>Null safe comparison of Comparables.</p>
358         *
359         * @param <T> type of the values processed by this method
360         * @param values the set of comparable values, may be null
361         * @return
362         *  <ul>
363         *   <li>If any objects are non-null and unequal, the greater object.
364         *   <li>If all objects are non-null and equal, the first.
365         *   <li>If any of the comparables are null, the greater of the non-null objects.
366         *   <li>If all the comparables are null, null is returned.
367         *  </ul>
368         */
369        public static <T extends Comparable<? super T>> T max(T... values) {
370            T result = null;
371            if (values != null) {
372                for (T value : values) {
373                    if (compare(value, result, false) > 0) {
374                        result = value;
375                    }
376                }
377            }
378            return result;
379        }
380    
381        /**
382         * <p>Null safe comparison of Comparables.
383         * {@code null} is assumed to be less than a non-{@code null} value.</p>
384         *
385         * @param <T> type of the values processed by this method
386         * @param c1  the first comparable, may be null
387         * @param c2  the second comparable, may be null
388         * @return a negative value if c1 < c2, zero if c1 = c2
389         *  and a positive value if c1 > c2
390         */
391        public static <T extends Comparable<? super T>> int compare(T c1, T c2) {
392            return compare(c1, c2, false);
393        }
394    
395        /**
396         * <p>Null safe comparison of Comparables.</p>
397         *
398         * @param <T> type of the values processed by this method
399         * @param c1  the first comparable, may be null
400         * @param c2  the second comparable, may be null
401         * @param nullGreater if true {@code null} is considered greater
402         *  than a non-{@code null} value or if false {@code null} is
403         *  considered less than a Non-{@code null} value
404         * @return a negative value if c1 < c2, zero if c1 = c2
405         *  and a positive value if c1 > c2
406         * @see java.util.Comparator#compare(Object, Object)
407         */
408        public static <T extends Comparable<? super T>> int compare(T c1, T c2, boolean nullGreater) {
409            if (c1 == c2) {
410                return 0;
411            } else if (c1 == null) {
412                return nullGreater ? 1 : -1;
413            } else if (c2 == null) {
414                return nullGreater ? -1 : 1;
415            }
416            return c1.compareTo(c2);
417        }
418    
419        /**
420         * Find the "best guess" middle value among comparables. If there is an even
421         * number of total values, the lower of the two middle values will be returned.
422         * @param <T> type of values processed by this method
423         * @param items to compare
424         * @return T at middle position
425         * @throws NullPointerException if items is {@code null}
426         * @throws IllegalArgumentException if items is empty or contains {@code null} values
427         * @since 3.0.1
428         */
429        public static <T extends Comparable<? super T>> T median(T... items) {
430            Validate.notEmpty(items);
431            Validate.noNullElements(items);
432            TreeSet<T> sort = new TreeSet<T>();
433            Collections.addAll(sort, items);
434            @SuppressWarnings("unchecked") //we know all items added were T instances
435            T result = (T) sort.toArray()[(sort.size() - 1) / 2];
436            return result;
437        }
438    
439        /**
440         * Find the "best guess" middle value among comparables. If there is an even
441         * number of total values, the lower of the two middle values will be returned.
442         * @param <T> type of values processed by this method
443         * @param comparator to use for comparisons
444         * @param items to compare
445         * @return T at middle position
446         * @throws NullPointerException if items or comparator is {@code null}
447         * @throws IllegalArgumentException if items is empty or contains {@code null} values
448         * @since 3.0.1
449         */
450        public static <T> T median(Comparator<T> comparator, T... items) {
451            Validate.notEmpty(items, "null/empty items");
452            Validate.noNullElements(items);
453            Validate.notNull(comparator, "null comparator");
454            TreeSet<T> sort = new TreeSet<T>(comparator);
455            Collections.addAll(sort, items);
456            @SuppressWarnings("unchecked") //we know all items added were T instances
457            T result = (T) sort.toArray()[(sort.size() - 1) / 2];
458            return result;
459        }
460    
461        // Mode
462        //-----------------------------------------------------------------------
463        /**
464         * Find the most frequently occurring item.
465         * 
466         * @param <T> type of values processed by this method
467         * @param items to check
468         * @return most populous T, {@code null} if non-unique or no items supplied
469         * @since 3.0.1
470         */
471        public static <T> T mode(T... items) {
472            if (ArrayUtils.isNotEmpty(items)) {
473                HashMap<T, MutableInt> occurrences = new HashMap<T, MutableInt>(items.length);
474                for (T t : items) {
475                    MutableInt count = occurrences.get(t);
476                    if (count == null) {
477                        occurrences.put(t, new MutableInt(1));
478                    } else {
479                        count.increment();
480                    }
481                }
482                T result = null;
483                int max = 0;
484                for (Map.Entry<T, MutableInt> e : occurrences.entrySet()) {
485                    int cmp = e.getValue().intValue();
486                    if (cmp == max) {
487                        result = null;
488                    } else if (cmp > max) {
489                        max = cmp;
490                        result = e.getKey();
491                    }
492                }
493                return result;
494            }
495            return null;
496        }
497    
498        // cloning
499        //-----------------------------------------------------------------------
500        /**
501         * <p>Clone an object.</p>
502         *
503         * @param <T> the type of the object
504         * @param obj  the object to clone, null returns null
505         * @return the clone if the object implements {@link Cloneable} otherwise {@code null}
506         * @throws CloneFailedException if the object is cloneable and the clone operation fails
507         * @since 3.0
508         */
509        public static <T> T clone(final T obj) {
510            if (obj instanceof Cloneable) {
511                final Object result;
512                if (obj.getClass().isArray()) {
513                    final Class<?> componentType = obj.getClass().getComponentType();
514                    if (!componentType.isPrimitive()) {
515                        result = ((Object[]) obj).clone();
516                    } else {
517                        int length = Array.getLength(obj);
518                        result = Array.newInstance(componentType, length);
519                        while (length-- > 0) {
520                            Array.set(result, length, Array.get(obj, length));
521                        }
522                    }
523                } else {
524                    try {
525                        final Method clone = obj.getClass().getMethod("clone");
526                        result = clone.invoke(obj);
527                    } catch (final NoSuchMethodException e) {
528                        throw new CloneFailedException("Cloneable type "
529                            + obj.getClass().getName()
530                            + " has no clone method", e);
531                    } catch (final IllegalAccessException e) {
532                        throw new CloneFailedException("Cannot clone Cloneable type "
533                            + obj.getClass().getName(), e);
534                    } catch (final InvocationTargetException e) {
535                        throw new CloneFailedException("Exception cloning Cloneable type "
536                            + obj.getClass().getName(), e.getCause());
537                    }
538                }
539                @SuppressWarnings("unchecked")
540                final T checked = (T) result;
541                return checked;
542            }
543    
544            return null;
545        }
546    
547        /**
548         * <p>Clone an object if possible.</p>
549         *
550         * <p>This method is similar to {@link #clone(Object)}, but will return the provided
551         * instance as the return value instead of {@code null} if the instance
552         * is not cloneable. This is more convenient if the caller uses different
553         * implementations (e.g. of a service) and some of the implementations do not allow concurrent
554         * processing or have state. In such cases the implementation can simply provide a proper
555         * clone implementation and the caller's code does not have to change.</p>
556         *
557         * @param <T> the type of the object
558         * @param obj  the object to clone, null returns null
559         * @return the clone if the object implements {@link Cloneable} otherwise the object itself
560         * @throws CloneFailedException if the object is cloneable and the clone operation fails
561         * @since 3.0
562         */
563        public static <T> T cloneIfPossible(final T obj) {
564            final T clone = clone(obj);
565            return clone == null ? obj : clone;
566        }
567    
568        // Null
569        //-----------------------------------------------------------------------
570        /**
571         * <p>Class used as a null placeholder where {@code null}
572         * has another meaning.</p>
573         *
574         * <p>For example, in a {@code HashMap} the
575         * {@link java.util.HashMap#get(java.lang.Object)} method returns
576         * {@code null} if the {@code Map} contains {@code null} or if there is
577         * no matching key. The {@code Null} placeholder can be used to distinguish
578         * between these two cases.</p>
579         *
580         * <p>Another example is {@code Hashtable}, where {@code null}
581         * cannot be stored.</p>
582         */
583        public static class Null implements Serializable {
584            /**
585             * Required for serialization support. Declare serialization compatibility with Commons Lang 1.0
586             *
587             * @see java.io.Serializable
588             */
589            private static final long serialVersionUID = 7092611880189329093L;
590    
591            /**
592             * Restricted constructor - singleton.
593             */
594            Null() {
595                super();
596            }
597    
598            /**
599             * <p>Ensure singleton.</p>
600             *
601             * @return the singleton value
602             */
603            private Object readResolve() {
604                return ObjectUtils.NULL;
605            }
606        }
607    
608    }