    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
    021    /**
    022     * <p>Operations on <code>Object</code>.</p>
    023     *
    024     * <p>This class tries to handle <code>null</code> input gracefully.
    025     * An exception will generally not be thrown for a <code>null</code> input.
    026     * Each method documents its behaviour in more detail.</p>
    027     *
    028     * @author Apache Software Foundation
    029     * @author <a href="mailto:nissim@nksystems.com">Nissim Karpenstein</a>
    030     * @author <a href="mailto:janekdb@yahoo.co.uk">Janek Bogucki</a>
    031     * @author Daniel L. Rall
    032     * @author Gary Gregory
    033     * @author Mario Winterer
    034     * @author <a href="mailto:david@davidkarlsen.com">David J. M. Karlsen</a>
    035     * @since 1.0
    036     * @version $Id: ObjectUtils.java 905636 2010-02-02 14:03:32Z niallp $
    037     */
    038    public class ObjectUtils {
    039
    040        /**
    041         * <p>Singleton used as a <code>null</code> placeholder where
    042         * <code>null</code> has another meaning.</p>
    043         *
    044         * <p>For example, in a <code>HashMap</code> the
    045         * {@link java.util.HashMap#get(java.lang.Object)} method returns
    046         * <code>null</code> if the <code>Map</code> contains
    047         * <code>null</code> or if there is no matching key. The
    048         * <code>Null</code> placeholder can be used to distinguish between
    049         * these two cases.</p>
    050         *
    051         * <p>Another example is <code>Hashtable</code>, where <code>null</code>
    052         * cannot be stored.</p>
    053         *
    054         * <p>This instance is Serializable.</p>
    055         */
    056        public static final Null NULL = new Null();
    057
    058        /**
    059         * <p><code>ObjectUtils</code> instances should NOT be constructed in
    060         * standard programming. Instead, the class should be used as
    061         * <code>ObjectUtils.defaultIfNull("a","b");</code>.</p>
    062         *
    063         * <p>This constructor is public to permit tools that require a JavaBean instance
    064         * to operate.</p>
    065         */
    066        public ObjectUtils() {
    067            super();
    068        }
    069
    070        // Defaulting
    071        //-----------------------------------------------------------------------
    072        /**
    073         * <p>Returns a default value if the object passed is
    074         * <code>null</code>.</p>
    075         *
    076         * <pre>
    077         * ObjectUtils.defaultIfNull(null, null)      = null
    078         * ObjectUtils.defaultIfNull(null, "")        = ""
    079         * ObjectUtils.defaultIfNull(null, "zz")      = "zz"
    080         * ObjectUtils.defaultIfNull("abc", *)        = "abc"
    081         * ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE
    082         * </pre>
    083         *
    084         * @param object  the <code>Object</code> to test, may be <code>null</code>
    085         * @param defaultValue  the default value to return, may be <code>null</code>
    086         * @return <code>object</code> if it is not <code>null</code>, defaultValue otherwise
    087         */
    088        public static Object defaultIfNull(Object object, Object defaultValue) {
    089            return object != null ? object : defaultValue;
    090        }
    091
    092        /**
    093         * <p>Compares two objects for equality, where either one or both
    094         * objects may be <code>null</code>.</p>
    095         *
    096         * <pre>
    097         * ObjectUtils.equals(null, null)                  = true
    098         * ObjectUtils.equals(null, "")                    = false
    099         * ObjectUtils.equals("", null)                    = false
    100         * ObjectUtils.equals("", "")                      = true
    101         * ObjectUtils.equals(Boolean.TRUE, null)          = false
    102         * ObjectUtils.equals(Boolean.TRUE, "true")        = false
    103         * ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE)  = true
    104         * ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false
    105         * </pre>
    106         *
    107         * @param object1  the first object, may be <code>null</code>
    108         * @param object2  the second object, may be <code>null</code>
    109         * @return <code>true</code> if the values of both objects are the same
    110         */
    111        public static boolean equals(Object object1, Object object2) {
    112            if (object1 == object2) {
    113                return true;
    114            }
    115            if ((object1 == null) || (object2 == null)) {
    116                return false;
    117            }
    118            return object1.equals(object2);
    119        }
    120
    121        /**
    122         * <p>Gets the hash code of an object returning zero when the
    123         * object is <code>null</code>.</p>
    124         *
    125         * <pre>
    126         * ObjectUtils.hashCode(null)   = 0
    127         * ObjectUtils.hashCode(obj)    = obj.hashCode()
    128         * </pre>
    129         *
    130         * @param obj  the object to obtain the hash code of, may be <code>null</code>
    131         * @return the hash code of the object, or zero if null
    132         * @since 2.1
    133         */
    134        public static int hashCode(Object obj) {
    135            return (obj == null) ? 0 : obj.hashCode();
    136        }
    137
    138        // Identity ToString
    139        //-----------------------------------------------------------------------
    140        /**
    141         * <p>Gets the toString that would be produced by <code>Object</code>
    142         * if a class did not override toString itself. <code>null</code>
    143         * will return <code>null</code>.</p>
    144         *
    145         * <pre>
    146         * ObjectUtils.identityToString(null)         = null
    147         * ObjectUtils.identityToString("")           = "java.lang.String@1e23"
    148         * ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"
    149         * </pre>
    150         *
    151         * @param object  the object to create a toString for, may be
    152         *  <code>null</code>
    153         * @return the default toString text, or <code>null</code> if
    154         *  <code>null</code> passed in
    155         */
    156        public static String identityToString(Object object) {
    157            if (object == null) {
    158                return null;
    159            }
    160            StringBuffer buffer = new StringBuffer();
    161            identityToString(buffer, object);
    162            return buffer.toString();
    163        }
    164
    165        /**
    166         * <p>Appends the toString that would be produced by <code>Object</code>
    167         * if a class did not override toString itself. <code>null</code>
    168         * will throw a NullPointerException for either of the two parameters. </p>
    169         *
    170         * <pre>
    171         * ObjectUtils.identityToString(buf, "")            = buf.append("java.lang.String@1e23"
    172         * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa"
    173         * ObjectUtils.identityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
    174         * </pre>
    175         *
    176         * @param buffer  the buffer to append to
    177         * @param object  the object to create a toString for
    178         * @since 2.4
    179         */
    180        public static void identityToString(StringBuffer buffer, Object object) {
    181            if (object == null) {
    182                throw new NullPointerException("Cannot get the toString of a null identity");
    183            }
    184            buffer.append(object.getClass().getName())
    185                  .append('@')
    186                  .append(Integer.toHexString(System.identityHashCode(object)));
    187        }
    188
    189        /**
    190         * <p>Appends the toString that would be produced by <code>Object</code>
    191         * if a class did not override toString itself. <code>null</code>
    192         * will return <code>null</code>.</p>
    193         *
    194         * <pre>
    195         * ObjectUtils.appendIdentityToString(*, null)            = null
    196         * ObjectUtils.appendIdentityToString(null, "")           = "java.lang.String@1e23"
    197         * ObjectUtils.appendIdentityToString(null, Boolean.TRUE) = "java.lang.Boolean@7fa"
    198         * ObjectUtils.appendIdentityToString(buf, Boolean.TRUE)  = buf.append("java.lang.Boolean@7fa")
    199         * </pre>
    200         *
    201         * @param buffer  the buffer to append to, may be <code>null</code>
    202         * @param object  the object to create a toString for, may be <code>null</code>
    203         * @return the default toString text, or <code>null</code> if
    204         *  <code>null</code> passed in
    205         * @since 2.0
    206         * @deprecated The design of this method is bad - see LANG-360. Instead, use identityToString(StringBuffer, Object).
    207         */
    208        public static StringBuffer appendIdentityToString(StringBuffer buffer, Object object) {
    209            if (object == null) {
    210                return null;
    211            }
    212            if (buffer == null) {
    213                buffer = new StringBuffer();
    214            }
    215            return buffer
    216                .append(object.getClass().getName())
    217                .append('@')
    218                .append(Integer.toHexString(System.identityHashCode(object)));
    219        }
    220
    221        // ToString
    222        //-----------------------------------------------------------------------
    223        /**
    224         * <p>Gets the <code>toString</code> of an <code>Object</code> returning
    225         * an empty string ("") if <code>null</code> input.</p>
    226         *
    227         * <pre>
    228         * ObjectUtils.toString(null)         = ""
    229         * ObjectUtils.toString("")           = ""
    230         * ObjectUtils.toString("bat")        = "bat"
    231         * ObjectUtils.toString(Boolean.TRUE) = "true"
    232         * </pre>
    233         *
    234         * @see StringUtils#defaultString(String)
    235         * @see String#valueOf(Object)
    236         * @param obj  the Object to <code>toString</code>, may be null
    237         * @return the passed in Object's toString, or nullStr if <code>null</code> input
    238         * @since 2.0
    239         */
    240        public static String toString(Object obj) {
    241            return obj == null ? "" : obj.toString();
    242        }
    243
    244        /**
    245         * <p>Gets the <code>toString</code> of an <code>Object</code> returning
    246         * a specified text if <code>null</code> input.</p>
    247         *
    248         * <pre>
    249         * ObjectUtils.toString(null, null)           = null
    250         * ObjectUtils.toString(null, "null")         = "null"
    251         * ObjectUtils.toString("", "null")           = ""
    252         * ObjectUtils.toString("bat", "null")        = "bat"
    253         * ObjectUtils.toString(Boolean.TRUE, "null") = "true"
    254         * </pre>
    255         *
    256         * @see StringUtils#defaultString(String,String)
    257         * @see String#valueOf(Object)
    258         * @param obj  the Object to <code>toString</code>, may be null
    259         * @param nullStr  the String to return if <code>null</code> input, may be null
    260         * @return the passed in Object's toString, or nullStr if <code>null</code> input
    261         * @since 2.0
    262         */
    263        public static String toString(Object obj, String nullStr) {
    264            return obj == null ? nullStr : obj.toString();
    265        }
    266
    267        // Min/Max
    268        //-----------------------------------------------------------------------
    269        /**
    270         * Null safe comparison of Comparables.
    271         *
    272         * @param c1  the first comparable, may be null
    273         * @param c2  the second comparable, may be null
    274         * @return
    275         *  <ul>
    276         *   <li>If both objects are non-null and unequal, the lesser object.
    277         *   <li>If both objects are non-null and equal, c1.
    278         *   <li>If one of the comparables is null, the non-null object.
    279         *   <li>If both the comparables are null, null is returned.
    280         *  </ul>
    281         */
    282        public static Object min(Comparable c1, Comparable c2) {
    283            if (c1 != null && c2 != null) {
    284                return c1.compareTo(c2) < 1 ? c1 : c2;
    285            } else {
    286                return c1 != null ? c1 : c2;
    287            }
    288        }
    289
    290        /**
    291         * Null safe comparison of Comparables.
    292         *
    293         * @param c1  the first comparable, may be null
    294         * @param c2  the second comparable, may be null
    295         * @return
    296         *  <ul>
    297         *   <li>If both objects are non-null and unequal, the greater object.
    298         *   <li>If both objects are non-null and equal, c1.
    299         *   <li>If one of the comparables is null, the non-null object.
    300         *   <li>If both the comparables are null, null is returned.
    301         *  </ul>
    302         */
    303        public static Object max(Comparable c1, Comparable c2) {
    304            if (c1 != null && c2 != null) {
    305                return c1.compareTo(c2) >= 0 ? c1 : c2;
    306            } else {
    307                return c1 != null ? c1 : c2;
    308            }
    309        }
    310
    311        // Null
    312        //-----------------------------------------------------------------------
    313        /**
    314         * <p>Class used as a null placeholder where <code>null</code>
    315         * has another meaning.</p>
    316         *
    317         * <p>For example, in a <code>HashMap</code> the
    318         * {@link java.util.HashMap#get(java.lang.Object)} method returns
    319         * <code>null</code> if the <code>Map</code> contains
    320         * <code>null</code> or if there is no matching key. The
    321         * <code>Null</code> placeholder can be used to distinguish between
    322         * these two cases.</p>
    323         *
    324         * <p>Another example is <code>Hashtable</code>, where <code>null</code>
    325         * cannot be stored.</p>
    326         */
    327        public static class Null implements Serializable {
    328            /**
    329             * Required for serialization support. Declare serialization compatibility with Commons Lang 1.0
    330             *
    331             * @see java.io.Serializable
    332             */
    333            private static final long serialVersionUID = 7092611880189329093L;
    334
    335            /**
    336             * Restricted constructor - singleton.
    337             */
    338            Null() {
    339                super();
    340            }
    341
    342            /**
    343             * <p>Ensure singleton.</p>
    344             *
    345             * @return the singleton value
    346             */
    347            private Object readResolve() {
    348                return ObjectUtils.NULL;
    349            }
    350        }
    351
    352    }