    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    }