Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.mawujun.util; import java.io.Serializable; import java.lang.reflect.Array; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.Arrays; import java.util.Collections; import java.util.Comparator; import java.util.HashMap; import java.util.Map; import java.util.TreeSet; import org.apache.commons.lang3.exception.CloneFailedException; import org.apache.commons.lang3.mutable.MutableInt; /** * <p>Operations on {@code Object}.</p> * * <p>This class tries to handle {@code null} input gracefully. * An exception will generally not be thrown for a {@code null} input. * Each method documents its behaviour in more detail.</p> * * <p>#ThreadSafe#</p> * @since 1.0 * @version $Id: ObjectUtils.java 1153350 2011-08-03 05:29:21Z bayard $ */ //@Immutable public class ObjectUtils { private static final int INITIAL_HASH = 7; private static final int MULTIPLIER = 31; private static final String EMPTY_STRING = ""; private static final String NULL_STRING = "null"; private static final String ARRAY_START = "{"; private static final String ARRAY_END = "}"; private static final String EMPTY_ARRAY = ARRAY_START + ARRAY_END; private static final String ARRAY_ELEMENT_SEPARATOR = ", "; /** * Return whether the given throwable is a checked exception: * that is, neither a RuntimeException nor an Error. * @param ex the throwable to check * @return whether the throwable is a checked exception * @see java.lang.Exception * @see java.lang.RuntimeException * @see java.lang.Error */ public static boolean isCheckedException(Throwable ex) { return !(ex instanceof RuntimeException || ex instanceof Error); } /** * Check whether the given exception is compatible with the exceptions * declared in a throws clause. * @param ex the exception to checked * @param declaredExceptions the exceptions declared in the throws clause * @return whether the given exception is compatible */ public static boolean isCompatibleWithThrowsClause(Throwable ex, Class[] declaredExceptions) { if (!isCheckedException(ex)) { return true; } if (declaredExceptions != null) { int i = 0; while (i < declaredExceptions.length) { if (declaredExceptions[i].isAssignableFrom(ex.getClass())) { return true; } i++; } } return false; } /** * Determine whether the given object is an array: * either an Object array or a primitive array. * @param obj the object to check */ public static boolean isArray(Object obj) { return (obj != null && obj.getClass().isArray()); } /** * Determine whether the given array is empty: * i.e. <code>null</code> or of zero length. * @param array the array to check */ public static boolean isEmpty(Object[] array) { return (array == null || array.length == 0); } /** * Check whether the given array contains the given element. * @param array the array to check (may be <code>null</code>, * in which case the return value will always be <code>false</code>) * @param element the element to check for * @return whether the element has been found in the given array */ public static boolean containsElement(Object[] array, Object element) { if (array == null) { return false; } for (Object arrayEle : array) { if (nullSafeEquals(arrayEle, element)) { return true; } } return false; } /** * Check whether the given array of enum constants contains a constant with the given name, * ignoring case when determining a match. * @param enumValues the enum values to check, typically the product of a call to MyEnum.values() * @param constant the constant name to find (must not be null or empty string) * @return whether the constant has been found in the given array */ public static boolean containsConstant(Enum<?>[] enumValues, String constant) { return containsConstant(enumValues, constant, false); } /** * Check whether the given array of enum constants contains a constant with the given name. * @param enumValues the enum values to check, typically the product of a call to MyEnum.values() * @param constant the constant name to find (must not be null or empty string) * @param caseSensitive whether case is significant in determining a match * @return whether the constant has been found in the given array */ public static boolean containsConstant(Enum<?>[] enumValues, String constant, boolean caseSensitive) { for (Enum<?> candidate : enumValues) { if (caseSensitive ? candidate.toString().equals(constant) : candidate.toString().equalsIgnoreCase(constant)) { return true; } } return false; } /** * Case insensitive alternative to {@link Enum#valueOf(Class, String)}. * @param <E> the concrete Enum type * @param enumValues the array of all Enum constants in question, usually per Enum.values() * @param constant the constant to get the enum value of * @throws IllegalArgumentException if the given constant is not found in the given array * of enum values. Use {@link #containsConstant(Enum[], String)} as a guard to avoid this exception. */ public static <E extends Enum<?>> E caseInsensitiveValueOf(E[] enumValues, String constant) { for (E candidate : enumValues) { if (candidate.toString().equalsIgnoreCase(constant)) { return candidate; } } throw new IllegalArgumentException(String.format("constant [%s] does not exist in enum type %s", constant, enumValues.getClass().getComponentType().getName())); } /** * Append the given object to the given array, returning a new array * consisting of the input array contents plus the given object. * @param array the array to append to (can be <code>null</code>) * @param obj the object to append * @return the new array (of the same component type; never <code>null</code>) */ public static <A, O extends A> A[] addObjectToArray(A[] array, O obj) { Class<?> compType = Object.class; if (array != null) { compType = array.getClass().getComponentType(); } else if (obj != null) { compType = obj.getClass(); } int newArrLength = (array != null ? array.length + 1 : 1); @SuppressWarnings("unchecked") A[] newArr = (A[]) Array.newInstance(compType, newArrLength); if (array != null) { System.arraycopy(array, 0, newArr, 0, array.length); } newArr[newArr.length - 1] = obj; return newArr; } /** * Convert the given array (which may be a primitive array) to an * object array (if necessary of primitive wrapper objects). * <p>A <code>null</code> source value will be converted to an * empty Object array. * @param source the (potentially primitive) array * @return the corresponding object array (never <code>null</code>) * @throws IllegalArgumentException if the parameter is not an array */ public static Object[] toObjectArray(Object source) { if (source instanceof Object[]) { return (Object[]) source; } if (source == null) { return new Object[0]; } if (!source.getClass().isArray()) { throw new IllegalArgumentException("Source is not an array: " + source); } int length = Array.getLength(source); if (length == 0) { return new Object[0]; } Class wrapperType = Array.get(source, 0).getClass(); Object[] newArray = (Object[]) Array.newInstance(wrapperType, length); for (int i = 0; i < length; i++) { newArray[i] = Array.get(source, i); } return newArray; } //--------------------------------------------------------------------- // Convenience methods for content-based equality/hash-code handling //--------------------------------------------------------------------- /** * Determine if the given objects are equal, returning <code>true</code> * if both are <code>null</code> or <code>false</code> if only one is * <code>null</code>. * <p>Compares arrays with <code>Arrays.equals</code>, performing an equality * check based on the array elements rather than the array reference. * @param o1 first Object to compare * @param o2 second Object to compare * @return whether the given objects are equal * @see java.util.Arrays#equals */ public static boolean nullSafeEquals(Object o1, Object o2) { if (o1 == o2) { return true; } if (o1 == null || o2 == null) { return false; } if (o1.equals(o2)) { return true; } if (o1.getClass().isArray() && o2.getClass().isArray()) { if (o1 instanceof Object[] && o2 instanceof Object[]) { return Arrays.equals((Object[]) o1, (Object[]) o2); } if (o1 instanceof boolean[] && o2 instanceof boolean[]) { return Arrays.equals((boolean[]) o1, (boolean[]) o2); } if (o1 instanceof byte[] && o2 instanceof byte[]) { return Arrays.equals((byte[]) o1, (byte[]) o2); } if (o1 instanceof char[] && o2 instanceof char[]) { return Arrays.equals((char[]) o1, (char[]) o2); } if (o1 instanceof double[] && o2 instanceof double[]) { return Arrays.equals((double[]) o1, (double[]) o2); } if (o1 instanceof float[] && o2 instanceof float[]) { return Arrays.equals((float[]) o1, (float[]) o2); } if (o1 instanceof int[] && o2 instanceof int[]) { return Arrays.equals((int[]) o1, (int[]) o2); } if (o1 instanceof long[] && o2 instanceof long[]) { return Arrays.equals((long[]) o1, (long[]) o2); } if (o1 instanceof short[] && o2 instanceof short[]) { return Arrays.equals((short[]) o1, (short[]) o2); } } return false; } /** * Return as hash code for the given object; typically the value of * <code>{@link Object#hashCode()}</code>. If the object is an array, * this method will delegate to any of the <code>nullSafeHashCode</code> * methods for arrays in this class. If the object is <code>null</code>, * this method returns 0. * @see #nullSafeHashCode(Object[]) * @see #nullSafeHashCode(boolean[]) * @see #nullSafeHashCode(byte[]) * @see #nullSafeHashCode(char[]) * @see #nullSafeHashCode(double[]) * @see #nullSafeHashCode(float[]) * @see #nullSafeHashCode(int[]) * @see #nullSafeHashCode(long[]) * @see #nullSafeHashCode(short[]) */ public static int nullSafeHashCode(Object obj) { if (obj == null) { return 0; } if (obj.getClass().isArray()) { if (obj instanceof Object[]) { return nullSafeHashCode((Object[]) obj); } if (obj instanceof boolean[]) { return nullSafeHashCode((boolean[]) obj); } if (obj instanceof byte[]) { return nullSafeHashCode((byte[]) obj); } if (obj instanceof char[]) { return nullSafeHashCode((char[]) obj); } if (obj instanceof double[]) { return nullSafeHashCode((double[]) obj); } if (obj instanceof float[]) { return nullSafeHashCode((float[]) obj); } if (obj instanceof int[]) { return nullSafeHashCode((int[]) obj); } if (obj instanceof long[]) { return nullSafeHashCode((long[]) obj); } if (obj instanceof short[]) { return nullSafeHashCode((short[]) obj); } } return obj.hashCode(); } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(Object[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + nullSafeHashCode(array[i]); } return hash; } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(boolean[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + hashCode(array[i]); } return hash; } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(byte[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + array[i]; } return hash; } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(char[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + array[i]; } return hash; } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(double[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + hashCode(array[i]); } return hash; } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(float[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + hashCode(array[i]); } return hash; } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(int[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + array[i]; } return hash; } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(long[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + hashCode(array[i]); } return hash; } /** * Return a hash code based on the contents of the specified array. * If <code>array</code> is <code>null</code>, this method returns 0. */ public static int nullSafeHashCode(short[] array) { if (array == null) { return 0; } int hash = INITIAL_HASH; int arraySize = array.length; for (int i = 0; i < arraySize; i++) { hash = MULTIPLIER * hash + array[i]; } return hash; } /** * Return the same value as <code>{@link Boolean#hashCode()}</code>. * @see Boolean#hashCode() */ public static int hashCode(boolean bool) { return bool ? 1231 : 1237; } /** * Return the same value as <code>{@link Double#hashCode()}</code>. * @see Double#hashCode() */ public static int hashCode(double dbl) { long bits = Double.doubleToLongBits(dbl); return hashCode(bits); } /** * Return the same value as <code>{@link Float#hashCode()}</code>. * @see Float#hashCode() */ public static int hashCode(float flt) { return Float.floatToIntBits(flt); } /** * Return the same value as <code>{@link Long#hashCode()}</code>. * @see Long#hashCode() */ public static int hashCode(long lng) { return (int) (lng ^ (lng >>> 32)); } //--------------------------------------------------------------------- // Convenience methods for toString output //--------------------------------------------------------------------- // // /** // * Return a String representation of an object's overall identity. // * @param obj the object (may be <code>null</code>) // * @return the object's identity as String representation, // * or an empty String if the object was <code>null</code> // */ // public static String identityToString(Object obj) { // if (obj == null) { // return EMPTY_STRING; // } // return obj.getClass().getName() + "@" + getIdentityHexString(obj); // } /** * Return a hex String form of an object's identity hash code. * @param obj the object * @return the object's identity code in hex notation */ public static String getIdentityHexString(Object obj) { return Integer.toHexString(System.identityHashCode(obj)); } /** * Return a content-based String representation if <code>obj</code> is * not <code>null</code>; otherwise returns an empty String. * <p>Differs from {@link #nullSafeToString(Object)} in that it returns * an empty String rather than "null" for a <code>null</code> value. * @param obj the object to build a display String for * @return a display String representation of <code>obj</code> * @see #nullSafeToString(Object) */ public static String getDisplayString(Object obj) { if (obj == null) { return EMPTY_STRING; } return nullSafeToString(obj); } /** * Determine the class name for the given object. * <p>Returns <code>"null"</code> if <code>obj</code> is <code>null</code>. * @param obj the object to introspect (may be <code>null</code>) * @return the corresponding class name */ public static String nullSafeClassName(Object obj) { return (obj != null ? obj.getClass().getName() : NULL_STRING); } /** * Return a String representation of the specified Object. * <p>Builds a String representation of the contents in case of an array. * Returns <code>"null"</code> if <code>obj</code> is <code>null</code>. * @param obj the object to build a String representation for * @return a String representation of <code>obj</code> */ public static String nullSafeToString(Object obj) { if (obj == null) { return NULL_STRING; } if (obj instanceof String) { return (String) obj; } if (obj instanceof Object[]) { return nullSafeToString((Object[]) obj); } if (obj instanceof boolean[]) { return nullSafeToString((boolean[]) obj); } if (obj instanceof byte[]) { return nullSafeToString((byte[]) obj); } if (obj instanceof char[]) { return nullSafeToString((char[]) obj); } if (obj instanceof double[]) { return nullSafeToString((double[]) obj); } if (obj instanceof float[]) { return nullSafeToString((float[]) obj); } if (obj instanceof int[]) { return nullSafeToString((int[]) obj); } if (obj instanceof long[]) { return nullSafeToString((long[]) obj); } if (obj instanceof short[]) { return nullSafeToString((short[]) obj); } String str = obj.toString(); return (str != null ? str : EMPTY_STRING); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(Object[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append(String.valueOf(array[i])); } sb.append(ARRAY_END); return sb.toString(); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(boolean[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append(array[i]); } sb.append(ARRAY_END); return sb.toString(); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(byte[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append(array[i]); } sb.append(ARRAY_END); return sb.toString(); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(char[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append("'").append(array[i]).append("'"); } sb.append(ARRAY_END); return sb.toString(); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(double[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append(array[i]); } sb.append(ARRAY_END); return sb.toString(); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(float[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append(array[i]); } sb.append(ARRAY_END); return sb.toString(); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(int[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append(array[i]); } sb.append(ARRAY_END); return sb.toString(); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(long[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append(array[i]); } sb.append(ARRAY_END); return sb.toString(); } /** * Return a String representation of the contents of the specified array. * <p>The String representation consists of a list of the array's elements, * enclosed in curly braces (<code>"{}"</code>). Adjacent elements are separated * by the characters <code>", "</code> (a comma followed by a space). Returns * <code>"null"</code> if <code>array</code> is <code>null</code>. * @param array the array to build a String representation for * @return a String representation of <code>array</code> */ public static String nullSafeToString(short[] array) { if (array == null) { return NULL_STRING; } int length = array.length; if (length == 0) { return EMPTY_ARRAY; } StringBuilder sb = new StringBuilder(); for (int i = 0; i < length; i++) { if (i == 0) { sb.append(ARRAY_START); } else { sb.append(ARRAY_ELEMENT_SEPARATOR); } sb.append(array[i]); } sb.append(ARRAY_END); return sb.toString(); } /** * <p>Singleton used as a {@code null} placeholder where * {@code null} has another meaning.</p> * * <p>For example, in a {@code HashMap} the * {@link java.util.HashMap#get(java.lang.Object)} method returns * {@code null} if the {@code Map} contains {@code null} or if there * is no matching key. The {@code Null} placeholder can be used to * distinguish between these two cases.</p> * * <p>Another example is {@code Hashtable}, where {@code null} * cannot be stored.</p> * * <p>This instance is Serializable.</p> */ public static final Null NULL = new Null(); /** * <p>{@code ObjectUtils} instances should NOT be constructed in * standard programming. Instead, the static methods on the class should * be used, such as {@code ObjectUtils.defaultIfNull("a","b");}.</p> * * <p>This constructor is public to permit tools that require a JavaBean * instance to operate.</p> */ public ObjectUtils() { super(); } // Defaulting //----------------------------------------------------------------------- /** * <p>Returns a default value if the object passed is {@code null}.</p> * * <pre> * ObjectUtils.defaultIfNull(null, null) = null * ObjectUtils.defaultIfNull(null, "") = "" * ObjectUtils.defaultIfNull(null, "zz") = "zz" * ObjectUtils.defaultIfNull("abc", *) = "abc" * ObjectUtils.defaultIfNull(Boolean.TRUE, *) = Boolean.TRUE * </pre> * * @param <T> the type of the object * @param object the {@code Object} to test, may be {@code null} * @param defaultValue the default value to return, may be {@code null} * @return {@code object} if it is not {@code null}, defaultValue otherwise */ public static <T> T defaultIfNull(T object, T defaultValue) { return object != null ? object : defaultValue; } /** * <p>Returns the first value in the array which is not {@code null}. * If all the values are {@code null} or the array is {@code null} * or empty then {@code null} is returned.</p> * * <pre> * ObjectUtils.firstNonNull(null, null) = null * ObjectUtils.firstNonNull(null, "") = "" * ObjectUtils.firstNonNull(null, null, "") = "" * ObjectUtils.firstNonNull(null, "zz") = "zz" * ObjectUtils.firstNonNull("abc", *) = "abc" * ObjectUtils.firstNonNull(null, "xyz", *) = "xyz" * ObjectUtils.firstNonNull(Boolean.TRUE, *) = Boolean.TRUE * ObjectUtils.firstNonNull() = null * </pre> * * @param <T> the component type of the array * @param values the values to test, may be {@code null} or empty * @return the first value from {@code values} which is not {@code null}, * or {@code null} if there are no non-null values * @since 3.0 */ public static <T> T firstNonNull(T... values) { if (values != null) { for (T val : values) { if (val != null) { return val; } } } return null; } // Null-safe equals/hashCode //----------------------------------------------------------------------- /** * <p>Compares two objects for equality, where either one or both * objects may be {@code null}.</p> * * <pre> * ObjectUtils.equals(null, null) = true * ObjectUtils.equals(null, "") = false * ObjectUtils.equals("", null) = false * ObjectUtils.equals("", "") = true * ObjectUtils.equals(Boolean.TRUE, null) = false * ObjectUtils.equals(Boolean.TRUE, "true") = false * ObjectUtils.equals(Boolean.TRUE, Boolean.TRUE) = true * ObjectUtils.equals(Boolean.TRUE, Boolean.FALSE) = false * </pre> * * @param object1 the first object, may be {@code null} * @param object2 the second object, may be {@code null} * @return {@code true} if the values of both objects are the same */ public static boolean equals(Object object1, Object object2) { if (object1 == object2) { return true; } if ((object1 == null) || (object2 == null)) { return false; } return object1.equals(object2); } /** * <p>Compares two objects for inequality, where either one or both * objects may be {@code null}.</p> * * <pre> * ObjectUtils.notEqual(null, null) = false * ObjectUtils.notEqual(null, "") = true * ObjectUtils.notEqual("", null) = true * ObjectUtils.notEqual("", "") = false * ObjectUtils.notEqual(Boolean.TRUE, null) = true * ObjectUtils.notEqual(Boolean.TRUE, "true") = true * ObjectUtils.notEqual(Boolean.TRUE, Boolean.TRUE) = false * ObjectUtils.notEqual(Boolean.TRUE, Boolean.FALSE) = true * </pre> * * @param object1 the first object, may be {@code null} * @param object2 the second object, may be {@code null} * @return {@code false} if the values of both objects are the same */ public static boolean notEqual(Object object1, Object object2) { return ObjectUtils.equals(object1, object2) == false; } /** * <p>Gets the hash code of an object returning zero when the * object is {@code null}.</p> * * <pre> * ObjectUtils.hashCode(null) = 0 * ObjectUtils.hashCode(obj) = obj.hashCode() * </pre> * * @param obj the object to obtain the hash code of, may be {@code null} * @return the hash code of the object, or zero if null * @since 2.1 */ public static int hashCode(Object obj) { // hashCode(Object) retained for performance, as hash code is often critical return (obj == null) ? 0 : obj.hashCode(); } /** * <p>Gets the hash code for multiple objects.</p> * * <p>This allows a hash code to be rapidly calculated for a number of objects. * The hash code for a single object is the <em>not</em> same as {@link #hashCode(Object)}. * The hash code for multiple objects is the same as that calculated by an * {@code ArrayList} containing the specified objects.</p> * * <pre> * ObjectUtils.hashCodeMulti() = 1 * ObjectUtils.hashCodeMulti((Object[]) null) = 1 * ObjectUtils.hashCodeMulti(a) = 31 + a.hashCode() * ObjectUtils.hashCodeMulti(a,b) = (31 + a.hashCode()) * 31 + b.hashCode() * ObjectUtils.hashCodeMulti(a,b,c) = ((31 + a.hashCode()) * 31 + b.hashCode()) * 31 + c.hashCode() * </pre> * * @param objects the objects to obtain the hash code of, may be {@code null} * @return the hash code of the objects, or zero if null * @since 3.0 */ public static int hashCodeMulti(Object... objects) { int hash = 1; if (objects != null) { for (Object object : objects) { hash = hash * 31 + ObjectUtils.hashCode(object); } } return hash; } // Identity ToString //----------------------------------------------------------------------- /** * <p>Gets the toString that would be produced by {@code Object} * if a class did not override toString itself. {@code null} * will return {@code null}.</p> * * <pre> * ObjectUtils.identityToString(null) = null * ObjectUtils.identityToString("") = "java.lang.String@1e23" * ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa" * </pre> * * @param object the object to create a toString for, may be * {@code null} * @return the default toString text, or {@code null} if * {@code null} passed in */ public static String identityToString(Object object) { if (object == null) { return null; } StringBuffer buffer = new StringBuffer(); identityToString(buffer, object); return buffer.toString(); } /** * <p>Appends the toString that would be produced by {@code Object} * if a class did not override toString itself. {@code null} * will throw a NullPointerException for either of the two parameters. </p> * * <pre> * ObjectUtils.identityToString(buf, "") = buf.append("java.lang.String@1e23" * ObjectUtils.identityToString(buf, Boolean.TRUE) = buf.append("java.lang.Boolean@7fa" * ObjectUtils.identityToString(buf, Boolean.TRUE) = buf.append("java.lang.Boolean@7fa") * </pre> * * @param buffer the buffer to append to * @param object the object to create a toString for * @since 2.4 */ public static void identityToString(StringBuffer buffer, Object object) { if (object == null) { throw new NullPointerException("Cannot get the toString of a null identity"); } buffer.append(object.getClass().getName()).append('@') .append(Integer.toHexString(System.identityHashCode(object))); } // ToString //----------------------------------------------------------------------- /** * <p>Gets the {@code toString} of an {@code Object} returning * an empty string ("") if {@code null} input.</p> * * <pre> * ObjectUtils.toString(null) = "" * ObjectUtils.toString("") = "" * ObjectUtils.toString("bat") = "bat" * ObjectUtils.toString(Boolean.TRUE) = "true" * </pre> * * @see StringUtils#defaultString(String) * @see String#valueOf(Object) * @param obj the Object to {@code toString}, may be null * @return the passed in Object's toString, or nullStr if {@code null} input * @since 2.0 */ public static String toString(Object obj) { return obj == null ? "" : obj.toString(); } /** * <p>Gets the {@code toString} of an {@code Object} returning * a specified text if {@code null} input.</p> * * <pre> * ObjectUtils.toString(null, null) = null * ObjectUtils.toString(null, "null") = "null" * ObjectUtils.toString("", "null") = "" * ObjectUtils.toString("bat", "null") = "bat" * ObjectUtils.toString(Boolean.TRUE, "null") = "true" * </pre> * * @see StringUtils#defaultString(String,String) * @see String#valueOf(Object) * @param obj the Object to {@code toString}, may be null * @param nullStr the String to return if {@code null} input, may be null * @return the passed in Object's toString, or nullStr if {@code null} input * @since 2.0 */ public static String toString(Object obj, String nullStr) { return obj == null ? nullStr : obj.toString(); } // Comparable //----------------------------------------------------------------------- /** * <p>Null safe comparison of Comparables.</p> * * @param <T> type of the values processed by this method * @param values the set of comparable values, may be null * @return * <ul> * <li>If any objects are non-null and unequal, the lesser object. * <li>If all objects are non-null and equal, the first. * <li>If any of the comparables are null, the lesser of the non-null objects. * <li>If all the comparables are null, null is returned. * </ul> */ public static <T extends Comparable<? super T>> T min(T... values) { T result = null; if (values != null) { for (T value : values) { if (compare(value, result, true) < 0) { result = value; } } } return result; } /** * <p>Null safe comparison of Comparables.</p> * * @param <T> type of the values processed by this method * @param values the set of comparable values, may be null * @return * <ul> * <li>If any objects are non-null and unequal, the greater object. * <li>If all objects are non-null and equal, the first. * <li>If any of the comparables are null, the greater of the non-null objects. * <li>If all the comparables are null, null is returned. * </ul> */ public static <T extends Comparable<? super T>> T max(T... values) { T result = null; if (values != null) { for (T value : values) { if (compare(value, result, false) > 0) { result = value; } } } return result; } /** * <p>Null safe comparison of Comparables. * {@code null} is assumed to be less than a non-{@code null} value.</p> * * @param <T> type of the values processed by this method * @param c1 the first comparable, may be null * @param c2 the second comparable, may be null * @return a negative value if c1 < c2, zero if c1 = c2 * and a positive value if c1 > c2 */ public static <T extends Comparable<? super T>> int compare(T c1, T c2) { return compare(c1, c2, false); } /** * <p>Null safe comparison of Comparables.</p> * * @param <T> type of the values processed by this method * @param c1 the first comparable, may be null * @param c2 the second comparable, may be null * @param nullGreater if true {@code null} is considered greater * than a non-{@code null} value or if false {@code null} is * considered less than a Non-{@code null} value * @return a negative value if c1 < c2, zero if c1 = c2 * and a positive value if c1 > c2 * @see java.util.Comparator#compare(Object, Object) */ public static <T extends Comparable<? super T>> int compare(T c1, T c2, boolean nullGreater) { if (c1 == c2) { return 0; } else if (c1 == null) { return (nullGreater ? 1 : -1); } else if (c2 == null) { return (nullGreater ? -1 : 1); } return c1.compareTo(c2); } /** * Find the "best guess" middle value among comparables. If there is an even * number of total values, the lower of the two middle values will be returned. * @param <T> type of values processed by this method * @param items to compare * @return T at middle position * @throws NullPointerException if items is {@code null} * @throws IllegalArgumentException if items is empty or contains {@code null} values * @since 3.0.1 */ public static <T extends Comparable<? super T>> T median(T... items) { Validate.notEmpty(items); Validate.noNullElements(items); TreeSet<T> sort = new TreeSet<T>(); Collections.addAll(sort, items); @SuppressWarnings("unchecked") //we know all items added were T instances T result = (T) sort.toArray()[(sort.size() - 1) / 2]; return result; } /** * Find the "best guess" middle value among comparables. If there is an even * number of total values, the lower of the two middle values will be returned. * @param <T> type of values processed by this method * @param comparator to use for comparisons * @param items to compare * @return T at middle position * @throws NullPointerException if items or comparator is {@code null} * @throws IllegalArgumentException if items is empty or contains {@code null} values * @since 3.0.1 */ public static <T> T median(Comparator<T> comparator, T... items) { Validate.notEmpty(items, "null/empty items"); Validate.noNullElements(items); Validate.notNull(comparator, "null comparator"); TreeSet<T> sort = new TreeSet<T>(comparator); Collections.addAll(sort, items); @SuppressWarnings("unchecked") //we know all items added were T instances T result = (T) sort.toArray()[(sort.size() - 1) / 2]; return result; } // Mode //----------------------------------------------------------------------- /** * Find the most frequently occurring item. * * @param <T> type of values processed by this method * @param items to check * @return most populous T, {@code null} if non-unique or no items supplied * @since 3.0.1 */ public static <T> T mode(T... items) { if (ArrayUtils.isNotEmpty(items)) { HashMap<T, MutableInt> occurrences = new HashMap<T, MutableInt>(items.length); for (T t : items) { MutableInt count = occurrences.get(t); if (count == null) { occurrences.put(t, new MutableInt(1)); } else { count.increment(); } } T result = null; int max = 0; for (Map.Entry<T, MutableInt> e : occurrences.entrySet()) { int cmp = e.getValue().intValue(); if (cmp == max) { result = null; } else if (cmp > max) { max = cmp; result = e.getKey(); } } return result; } return null; } // cloning //----------------------------------------------------------------------- /** * <p>Clone an object.</p> * * @param <T> the type of the object * @param obj the object to clone, null returns null * @return the clone if the object implements {@link Cloneable} otherwise {@code null} * @throws CloneFailedException if the object is cloneable and the clone operation fails * @since 3.0 */ public static <T> T clone(final T obj) { if (obj instanceof Cloneable) { final Object result; if (obj.getClass().isArray()) { final Class<?> componentType = obj.getClass().getComponentType(); if (!componentType.isPrimitive()) { result = ((Object[]) obj).clone(); } else { int length = Array.getLength(obj); result = Array.newInstance(componentType, length); while (length-- > 0) { Array.set(result, length, Array.get(obj, length)); } } } else { try { final Method clone = obj.getClass().getMethod("clone"); result = clone.invoke(obj); } catch (final NoSuchMethodException e) { throw new CloneFailedException( "Cloneable type " + obj.getClass().getName() + " has no clone method", e); } catch (final IllegalAccessException e) { throw new CloneFailedException("Cannot clone Cloneable type " + obj.getClass().getName(), e); } catch (final InvocationTargetException e) { throw new CloneFailedException("Exception cloning Cloneable type " + obj.getClass().getName(), e.getCause()); } } @SuppressWarnings("unchecked") final T checked = (T) result; return checked; } return null; } /** * <p>Clone an object if possible.</p> * * <p>This method is similar to {@link #clone(Object)}, but will return the provided * instance as the return value instead of {@code null} if the instance * is not cloneable. This is more convenient if the caller uses different * implementations (e.g. of a service) and some of the implementations do not allow concurrent * processing or have state. In such cases the implementation can simply provide a proper * clone implementation and the caller's code does not have to change.</p> * * @param <T> the type of the object * @param obj the object to clone, null returns null * @return the clone if the object implements {@link Cloneable} otherwise the object itself * @throws CloneFailedException if the object is cloneable and the clone operation fails * @since 3.0 */ public static <T> T cloneIfPossible(final T obj) { final T clone = clone(obj); return clone == null ? obj : clone; } // Null //----------------------------------------------------------------------- /** * <p>Class used as a null placeholder where {@code null} * has another meaning.</p> * * <p>For example, in a {@code HashMap} the * {@link java.util.HashMap#get(java.lang.Object)} method returns * {@code null} if the {@code Map} contains {@code null} or if there is * no matching key. The {@code Null} placeholder can be used to distinguish * between these two cases.</p> * * <p>Another example is {@code Hashtable}, where {@code null} * cannot be stored.</p> */ public static class Null implements Serializable { /** * Required for serialization support. Declare serialization compatibility with Commons Lang 1.0 * * @see java.io.Serializable */ private static final long serialVersionUID = 7092611880189329093L; /** * Restricted constructor - singleton. */ Null() { super(); } /** * <p>Ensure singleton.</p> * * @return the singleton value */ private Object readResolve() { return ObjectUtils.NULL; } } }