/*
 * 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
 *
 *      https://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 org.apache.commons.lang3;

import java.io.IOException;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.time.Duration;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.TreeSet;
import java.util.function.Consumer;
import java.util.function.Supplier;
import java.util.stream.Stream;

import org.apache.commons.lang3.exception.CloneFailedException;
import org.apache.commons.lang3.function.Consumers;
import org.apache.commons.lang3.function.Suppliers;
import org.apache.commons.lang3.mutable.MutableInt;
import org.apache.commons.lang3.stream.Streams;
import org.apache.commons.lang3.text.StrBuilder;
import org.apache.commons.lang3.time.DurationUtils;

/**
 * Operations on {@link Object}.
 *
 * <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 behavior in more detail.
 * </p>
 *
 * <p>#ThreadSafe#</p>
 *
 * @see Consumers
 * @see Suppliers
 * @since 1.0
 */
//@Immutable
@SuppressWarnings("deprecation") // deprecated class StrBuilder is imported
// because it is part of the signature of deprecated methods
public class ObjectUtils {

    /**
     * Class used as a null placeholder where {@code null} has another meaning.
     *
     * <p>
     * For example, in a {@link HashMap} the {@link java.util.HashMap#get(Object)} method returns {@code null} if the {@link 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 {@link 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() {
        }

        /**
         * Ensures singleton after serialization.
         *
         * @return the singleton value.
         */
        private Object readResolve() {
            return NULL;
        }
    }

    private static final char AT_SIGN = '@';

    /**
     * Singleton used as a {@code null} placeholder where {@code null} has another meaning.
     *
     * <p>
     * For example, in a {@link HashMap} the {@link java.util.HashMap#get(Object)} method returns {@code null} if the {@link 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 {@link Hashtable}, where {@code null} cannot be stored.
     * </p>
     *
     * <p>
     * This instance is Serializable.
     * </p>
     */
    public static final Null NULL = new Null();

    /**
     * Tests if all values in the array are not {@code nulls}.
     *
     * <p>
     * If any value is {@code null} or the array is {@code null} then {@code false} is returned. If all elements in array are not {@code null} or the array is
     * empty (contains no elements) {@code true} is returned.
     * </p>
     *
     * <pre>
     * ObjectUtils.allNotNull(*)             = true
     * ObjectUtils.allNotNull(*, *)          = true
     * ObjectUtils.allNotNull(null)          = false
     * ObjectUtils.allNotNull(null, null)    = false
     * ObjectUtils.allNotNull(null, *)       = false
     * ObjectUtils.allNotNull(*, null)       = false
     * ObjectUtils.allNotNull(*, *, null, *) = false
     * </pre>
     *
     * @param values the values to test, may be {@code null} or empty.
     * @return {@code false} if there is at least one {@code null} value in the array or the array is {@code null}, {@code true} if all values in the array are
     *         not {@code null}s or array contains no elements.
     * @since 3.5
     */
    public static boolean allNotNull(final Object... values) {
        return values != null && Stream.of(values).noneMatch(Objects::isNull);
    }

    /**
     * Tests if all values in the given array are {@code null}.
     *
     * <p>
     * If all the values are {@code null} or the array is {@code null} or empty, then {@code true} is returned, otherwise {@code false} is returned.
     * </p>
     *
     * <pre>
     * ObjectUtils.allNull(*)                = false
     * ObjectUtils.allNull(*, null)          = false
     * ObjectUtils.allNull(null, *)          = false
     * ObjectUtils.allNull(null, null, *, *) = false
     * ObjectUtils.allNull(null)             = true
     * ObjectUtils.allNull(null, null)       = true
     * </pre>
     *
     * @param values the values to test, may be {@code null} or empty.
     * @return {@code true} if all values in the array are {@code null}s, {@code false} if there is at least one non-null value in the array.
     * @since 3.11
     */
    public static boolean allNull(final Object... values) {
        return !anyNotNull(values);
    }

    /**
     * Tests if any value in the given array is not {@code null}.
     *
     * <p>
     * If all the values are {@code null} or the array is {@code null} or empty then {@code false} is returned. Otherwise {@code true} is returned.
     * </p>
     *
     * <pre>
     * ObjectUtils.anyNotNull(*)                = true
     * ObjectUtils.anyNotNull(*, null)          = true
     * ObjectUtils.anyNotNull(null, *)          = true
     * ObjectUtils.anyNotNull(null, null, *, *) = true
     * ObjectUtils.anyNotNull(null)             = false
     * ObjectUtils.anyNotNull(null, null)       = false
     * </pre>
     *
     * @param values the values to test, may be {@code null} or empty.
     * @return {@code true} if there is at least one non-null value in the array, {@code false} if all values in the array are {@code null}s. If the array is
     *         {@code null} or empty {@code false} is also returned.
     * @since 3.5
     */
    public static boolean anyNotNull(final Object... values) {
        return firstNonNull(values) != null;
    }

    /**
     * Tests if any value in the given array is {@code null}.
     *
     * <p>
     * If any of the values are {@code null} or the array is {@code null}, then {@code true} is returned, otherwise {@code false} is returned.
     * </p>
     *
     * <pre>
     * ObjectUtils.anyNull(*)             = false
     * ObjectUtils.anyNull(*, *)          = false
     * ObjectUtils.anyNull(null)          = true
     * ObjectUtils.anyNull(null, null)    = true
     * ObjectUtils.anyNull(null, *)       = true
     * ObjectUtils.anyNull(*, null)       = true
     * ObjectUtils.anyNull(*, *, null, *) = true
     * </pre>
     *
     * @param values the values to test, may be {@code null} or empty.
     * @return {@code true} if there is at least one {@code null} value in the array, {@code false} if all the values are non-null. If the array is {@code null}
     *         or empty, {@code true} is also returned.
     * @since 3.11
     */
    public static boolean anyNull(final Object... values) {
        return !allNotNull(values);
    }

    /**
     * Clones an object.
     *
     * @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;
            final Class<? extends Object> objClass = obj.getClass();
            if (isArray(obj)) {
                final Class<?> componentType = objClass.getComponentType();
                if (componentType.isPrimitive()) {
                    int length = Array.getLength(obj);
                    result = Array.newInstance(componentType, length);
                    while (length-- > 0) {
                        Array.set(result, length, Array.get(obj, length));
                    }
                } else {
                    result = ((Object[]) obj).clone();
                }
            } else {
                try {
                    result = objClass.getMethod("clone").invoke(obj);
                } catch (final ReflectiveOperationException e) {
                    throw new CloneFailedException("Exception cloning Cloneable type " + objClass.getName(), e);
                }
            }
            return (T) result;
        }
        return null;
    }

    /**
     * Clones an object if possible.
     *
     * <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 safe comparison of Comparables. {@code null} is assumed to be less than a non-{@code null} value.
     * <p>
     * TODO Move to ComparableUtils.
     * </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 &lt; c2, zero if c1 = c2 and a positive value if c1 &gt; c2.
     */
    public static <T extends Comparable<? super T>> int compare(final T c1, final T c2) {
        return compare(c1, c2, false);
    }

    /**
     * Null safe comparison of Comparables.
     * <p>
     * TODO Move to ComparableUtils.
     * </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 &lt; c2, zero if c1 = c2 and a positive value if c1 &gt; c2.
     * @see java.util.Comparator#compare(Object, Object)
     */
    public static <T extends Comparable<? super T>> int compare(final T c1, final T c2, final boolean nullGreater) {
        if (c1 == c2) {
            return 0;
        }
        if (c1 == null) {
            return nullGreater ? 1 : -1;
        }
        if (c2 == null) {
            return nullGreater ? -1 : 1;
        }
        return c1.compareTo(c2);
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static boolean MAGIC_FLAG = ObjectUtils.CONST(true);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the boolean value to return.
     * @return the boolean v, unchanged.
     * @since 3.2
     */
    public static boolean CONST(final boolean v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static byte MAGIC_BYTE = ObjectUtils.CONST((byte) 127);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the byte value to return.
     * @return the byte v, unchanged.
     * @since 3.2
     */
    public static byte CONST(final byte v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static char MAGIC_CHAR = ObjectUtils.CONST('a');
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the char value to return.
     * @return the char v, unchanged.
     * @since 3.2
     */
    public static char CONST(final char v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static double MAGIC_DOUBLE = ObjectUtils.CONST(1.0);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the double value to return.
     * @return the double v, unchanged.
     * @since 3.2
     */
    public static double CONST(final double v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static float MAGIC_FLOAT = ObjectUtils.CONST(1.0f);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the float value to return.
     * @return the float v, unchanged.
     * @since 3.2
     */
    public static float CONST(final float v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static int MAGIC_INT = ObjectUtils.CONST(123);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the int value to return.
     * @return the int v, unchanged.
     * @since 3.2
     */
    public static int CONST(final int v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static long MAGIC_LONG = ObjectUtils.CONST(123L);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the long value to return.
     * @return the long v, unchanged.
     * @since 3.2
     */
    public static long CONST(final long v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static short MAGIC_SHORT = ObjectUtils.CONST((short) 123);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the short value to return.
     * @return the short v, unchanged.
     * @since 3.2
     */
    public static short CONST(final short v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static String MAGIC_STRING = ObjectUtils.CONST("abc");
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param <T> the Object type.
     * @param v   the genericized Object value to return (typically a String).
     * @return the genericized Object v, unchanged (typically a String).
     * @since 3.2
     */
    public static <T> T CONST(final T v) {
        return v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static byte MAGIC_BYTE = ObjectUtils.CONST_BYTE(127);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the byte literal (as an int) value to return.
     * @throws IllegalArgumentException if the value passed to v is larger than a byte, that is, smaller than -128 or larger than 127.
     * @return the byte v, unchanged.
     * @since 3.2
     */
    public static byte CONST_BYTE(final int v) {
        if (v < Byte.MIN_VALUE || v > Byte.MAX_VALUE) {
            throw new IllegalArgumentException("Supplied value must be a valid byte literal between -128 and 127: [" + v + "]");
        }
        return (byte) v;
    }

    /**
     * Returns the provided value unchanged. This can prevent javac from inlining a constant field, e.g.,
     *
     * <pre>
     * public final static short MAGIC_SHORT = ObjectUtils.CONST_SHORT(127);
     * </pre>
     *
     * This way any jars that refer to this field do not have to recompile themselves if the field's value changes at some future date.
     *
     * @param v the short literal (as an int) value to return.
     * @throws IllegalArgumentException if the value passed to v is larger than a short, that is, smaller than -32768 or larger than 32767.
     * @return the byte v, unchanged.
     * @since 3.2
     */
    public static short CONST_SHORT(final int v) {
        if (v < Short.MIN_VALUE || v > Short.MAX_VALUE) {
            throw new IllegalArgumentException("Supplied value must be a valid byte literal between -32768 and 32767: [" + v + "]");
        }
        return (short) v;
    }

    /**
     * Returns a default value if the object passed is {@code null}.
     *
     * <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 {@link 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.
     * @see #getIfNull(Object, Object)
     * @see #getIfNull(Object, Supplier)
     * @deprecated Use {@link #getIfNull(Object, Object)}.
     */
    @Deprecated
    public static <T> T defaultIfNull(final T object, final T defaultValue) {
        return getIfNull(object, defaultValue);
    }

    // Null-safe equals/hashCode
    /**
     * Compares two objects for equality, where either one or both
     * objects may be {@code null}.
     *
     * <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.
     * @deprecated this method has been replaced by {@code java.util.Objects.equals(Object, Object)} in Java 7 and will
     * be removed from future releases.
     */
    @Deprecated
    public static boolean equals(final Object object1, final Object object2) {
        return Objects.equals(object1, object2);
    }

    /**
     * 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.
     *
     * <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
     */
    @SafeVarargs
    public static <T> T firstNonNull(final T... values) {
        return Streams.of(values).filter(Objects::nonNull).findFirst().orElse(null);
    }

    /**
     * Delegates to {@link Object#getClass()} using generics.
     *
     * @param <T> The argument type or null.
     * @param object The argument.
     * @return The argument's Class or null.
     * @since 3.13.0
     */
    @SuppressWarnings("unchecked")
    public static <T> Class<T> getClass(final T object) {
        return object == null ? null : (Class<T>) object.getClass();
    }

    /**
     * Executes the given suppliers in order and returns the first return value where a value other than {@code null} is returned. Once a non-{@code null} value
     * is obtained, all following suppliers are not executed anymore. If all the return values are {@code null} or no suppliers are provided then {@code null}
     * is returned.
     *
     * <pre>{@code
     * ObjectUtils.firstNonNullLazy(null, () -> null)                                  = null
     * ObjectUtils.firstNonNullLazy(() -> null, () -> "")                              = ""
     * ObjectUtils.firstNonNullLazy(() -> "", () -> throw new IllegalStateException()) = ""
     * ObjectUtils.firstNonNullLazy(() -> null, () -> "zz)                             = "zz"
     * ObjectUtils.firstNonNullLazy()                                                  = null
     * }</pre>
     * <p>
     * See also {@link Consumers#accept(Consumer, Object)} and {@link Suppliers#get(Supplier)}.
     * </p>
     *
     * @param <T>       the type of the return values.
     * @param suppliers the suppliers returning the values to test. {@code null} values are ignored. Suppliers may return {@code null} or a value of type
     *                  {@code T}.
     * @return the first return value from {@code suppliers} which is not {@code null}, or {@code null} if there are no non-null values.
     * @see Consumers#accept(Consumer, Object)
     * @see Suppliers#get(Supplier)
     * @since 3.10
     */
    @SafeVarargs
    public static <T> T getFirstNonNull(final Supplier<T>... suppliers) {
        return Streams.of(suppliers).filter(Objects::nonNull).map(Supplier::get).filter(Objects::nonNull).findFirst().orElse(null);
    }

    /**
     * Returns the given {@code object} is it is non-null, otherwise returns the Supplier's {@link Supplier#get()}
     * value.
     *
     * <p>
     * The caller responsible for thread-safety and exception handling of default value supplier.
     * </p>
     *
     * <pre>{@code
     * ObjectUtils.getIfNull(null, () -> null)     = null
     * ObjectUtils.getIfNull(null, null)           = null
     * ObjectUtils.getIfNull(null, () -> "")       = ""
     * ObjectUtils.getIfNull(null, () -> "zz")     = "zz"
     * ObjectUtils.getIfNull("abc", *)             = "abc"
     * ObjectUtils.getIfNull(Boolean.TRUE, *)      = Boolean.TRUE
     * }</pre>
     * <p>
     * See also {@link Consumers#accept(Consumer, Object)} and {@link Suppliers#get(Supplier)}.
     * </p>
     *
     * @param <T> the type of the object.
     * @param object the {@link Object} to test, may be {@code null}.
     * @param defaultSupplier the default value to return, may be {@code null}.
     * @return {@code object} if it is not {@code null}, {@code defaultValueSupplier.get()} otherwise.
     * @see #getIfNull(Object, Object)
     * @see Consumers#accept(Consumer, Object)
     * @see Suppliers#get(Supplier)
     * @since 3.10
     */
    public static <T> T getIfNull(final T object, final Supplier<T> defaultSupplier) {
        return object != null ? object : Suppliers.get(defaultSupplier);
    }

    /**
     * Returns a default value if the object passed is {@code null}.
     *
     * <pre>
     * ObjectUtils.getIfNull(null, null)      = null
     * ObjectUtils.getIfNull(null, "")        = ""
     * ObjectUtils.getIfNull(null, "zz")      = "zz"
     * ObjectUtils.getIfNull("abc", *)        = "abc"
     * ObjectUtils.getIfNull(Boolean.TRUE, *) = Boolean.TRUE
     * </pre>
     * <p>
     * See also {@link Consumers#accept(Consumer, Object)} and {@link Suppliers#get(Supplier)}.
     * </p>
     *
     * @param <T> the type of the object.
     * @param object  the {@link 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.
     * @see #getIfNull(Object, Supplier)
     * @see Consumers#accept(Consumer, Object)
     * @see Suppliers#get(Supplier)
     * @since 3.18.0
     */
    public static <T> T getIfNull(final T object, final T defaultValue) {
        return object != null ? object : defaultValue;
    }

    /**
     * Gets the hash code of an object returning zero when the object is {@code null}.
     *
     * <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
     * @deprecated this method has been replaced by {@code java.util.Objects.hashCode(Object)} in Java 7 and will be removed in future releases.
     */
    @Deprecated
    public static int hashCode(final Object obj) {
        // hashCode(Object) for performance vs. hashCodeMulti(Object[]), as hash code is often critical
        return Objects.hashCode(obj);
    }

    /**
     * Returns the hexadecimal hash code for the given object per {@link Objects#hashCode(Object)}.
     * <p>
     * Short hand for {@code Integer.toHexString(Objects.hashCode(object))}.
     * </p>
     *
     * @param object object for which the hashCode is to be calculated.
     * @return Hash code in hexadecimal format.
     * @since 3.13.0
     */
    public static String hashCodeHex(final Object object) {
        return Integer.toHexString(Objects.hashCode(object));
    }

    /**
     * Gets the hash code for multiple objects.
     *
     * <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 {@link 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
     * @deprecated this method has been replaced by {@code java.util.Objects.hash(Object...)} in Java 7 and will be removed in future releases.
     */
    @Deprecated
    public static int hashCodeMulti(final Object... objects) {
        int hash = 1;
        if (objects != null) {
            for (final Object object : objects) {
                final int tmpHash = Objects.hashCode(object);
                hash = hash * 31 + tmpHash;
            }
        }
        return hash;
    }

    /**
     * Returns the hexadecimal hash code for the given object per {@link System#identityHashCode(Object)}.
     * <p>
     * Short hand for {@code Integer.toHexString(System.identityHashCode(object))}.
     * </p>
     *
     * @param object object for which the hashCode is to be calculated.
     * @return Hash code in hexadecimal format.
     * @since 3.13.0
     */
    public static String identityHashCodeHex(final Object object) {
        return Integer.toHexString(System.identityHashCode(object));
    }

    /**
     * Appends the toString that would be produced by {@link Object}
     * if a class did not override toString itself. {@code null}
     * will throw a NullPointerException for either of the two parameters.
     *
     * <pre>
     * ObjectUtils.identityToString(appendable, "")            = appendable.append("java.lang.String@1e23")
     * ObjectUtils.identityToString(appendable, Boolean.TRUE)  = appendable.append("java.lang.Boolean@7fa")
     * ObjectUtils.identityToString(appendable, Boolean.TRUE)  = appendable.append("java.lang.Boolean@7fa")
     * </pre>
     *
     * @param appendable  the appendable to append to.
     * @param object  the object to create a toString for.
     * @throws IOException if an I/O error occurs.
     * @since 3.2
     */
    public static void identityToString(final Appendable appendable, final Object object) throws IOException {
        Objects.requireNonNull(object, "object");
        appendable.append(object.getClass().getName())
              .append(AT_SIGN)
              .append(identityHashCodeHex(object));
    }

    /**
     * Gets the toString that would be produced by {@link Object} if a class did not override toString itself. {@code null} will return {@code null}.
     *
     * <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(final Object object) {
        if (object == null) {
            return null;
        }
        final String name = object.getClass().getName();
        final String hexString = identityHashCodeHex(object);
        final StringBuilder builder = new StringBuilder(name.length() + 1 + hexString.length());
        // @formatter:off
        builder.append(name)
              .append(AT_SIGN)
              .append(hexString);
        // @formatter:on
        return builder.toString();
    }

    /**
     * Appends the toString that would be produced by {@link Object}
     * if a class did not override toString itself. {@code null}
     * will throw a NullPointerException for either of the two parameters.
     *
     * <pre>
     * ObjectUtils.identityToString(builder, "")            = builder.append("java.lang.String@1e23")
     * ObjectUtils.identityToString(builder, Boolean.TRUE)  = builder.append("java.lang.Boolean@7fa")
     * ObjectUtils.identityToString(builder, Boolean.TRUE)  = builder.append("java.lang.Boolean@7fa")
     * </pre>
     *
     * @param builder  the builder to append to.
     * @param object  the object to create a toString for.
     * @since 3.2
     * @deprecated as of 3.6, because StrBuilder was moved to commons-text,
     *  use one of the other {@code identityToString} methods instead.
     */
    @Deprecated
    public static void identityToString(final StrBuilder builder, final Object object) {
        Objects.requireNonNull(object, "object");
        final String name = object.getClass().getName();
        final String hexString = identityHashCodeHex(object);
        builder.ensureCapacity(builder.length() +  name.length() + 1 + hexString.length());
        builder.append(name)
              .append(AT_SIGN)
              .append(hexString);
    }

    /**
     * Appends the toString that would be produced by {@link Object}
     * if a class did not override toString itself. {@code null}
     * will throw a NullPointerException for either of the two parameters.
     *
     * <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(final StringBuffer buffer, final Object object) {
        Objects.requireNonNull(object, "object");
        final String name = object.getClass().getName();
        final String hexString = identityHashCodeHex(object);
        buffer.ensureCapacity(buffer.length() + name.length() + 1 + hexString.length());
        buffer.append(name)
              .append(AT_SIGN)
              .append(hexString);
    }

    /**
     * Appends the toString that would be produced by {@link Object}
     * if a class did not override toString itself. {@code null}
     * will throw a NullPointerException for either of the two parameters.
     *
     * <pre>
     * ObjectUtils.identityToString(builder, "")            = builder.append("java.lang.String@1e23")
     * ObjectUtils.identityToString(builder, Boolean.TRUE)  = builder.append("java.lang.Boolean@7fa")
     * ObjectUtils.identityToString(builder, Boolean.TRUE)  = builder.append("java.lang.Boolean@7fa")
     * </pre>
     *
     * @param builder  the builder to append to.
     * @param object  the object to create a toString for.
     * @since 3.2
     */
    public static void identityToString(final StringBuilder builder, final Object object) {
        Objects.requireNonNull(object, "object");
        final String name = object.getClass().getName();
        final String hexString = identityHashCodeHex(object);
        builder.ensureCapacity(builder.length() +  name.length() + 1 + hexString.length());
        builder.append(name)
              .append(AT_SIGN)
              .append(hexString);
    }

    /**
     * Tests whether the given object is an Object array or a primitive array in a null-safe manner.
     *
     * <p>
     * A {@code null} {@code object} Object will return {@code false}.
     * </p>
     *
     * <pre>
     * ObjectUtils.isArray(null)             = false
     * ObjectUtils.isArray("")               = false
     * ObjectUtils.isArray("ab")             = false
     * ObjectUtils.isArray(new int[]{})      = true
     * ObjectUtils.isArray(new int[]{1,2,3}) = true
     * ObjectUtils.isArray(1234)             = false
     * </pre>
     *
     * @param object the object to check, may be {@code null}.
     * @return {@code true} if the object is an {@code array}, {@code false} otherwise.
     * @since 3.13.0
     */
    public static boolean isArray(final Object object) {
        return object != null && object.getClass().isArray();
    }

    /**
     * Tests if an Object is empty or null.
     * <p>
     * The following types are supported:
     * </p>
     * <ul>
     * <li>{@link CharSequence}: Considered empty if its length is zero.</li>
     * <li>{@link Array}: Considered empty if its length is zero.</li>
     * <li>{@link Collection}: Considered empty if it has zero elements.</li>
     * <li>{@link Map}: Considered empty if it has zero key-value mappings.</li>
     * <li>{@link Optional}: Considered empty if {@link Optional#isPresent} returns false, regardless of the "emptiness" of the contents.</li>
     * </ul>
     *
     * <pre>
     * ObjectUtils.isEmpty(null)             = true
     * ObjectUtils.isEmpty("")               = true
     * ObjectUtils.isEmpty("ab")             = false
     * ObjectUtils.isEmpty(new int[]{})      = true
     * ObjectUtils.isEmpty(new int[]{1,2,3}) = false
     * ObjectUtils.isEmpty(1234)             = false
     * ObjectUtils.isEmpty(1234)             = false
     * ObjectUtils.isEmpty(Optional.of(""))  = false
     * ObjectUtils.isEmpty(Optional.empty()) = true
     * </pre>
     *
     * @param object the {@link Object} to test, may be {@code null}.
     * @return {@code true} if the object has a supported type and is empty or null, {@code false} otherwise.
     * @since 3.9
     */
    public static boolean isEmpty(final Object object) {
        if (object == null) {
            return true;
        }
        if (object instanceof CharSequence) {
            return ((CharSequence) object).length() == 0;
        }
        if (isArray(object)) {
            return Array.getLength(object) == 0;
        }
        if (object instanceof Collection<?>) {
            return ((Collection<?>) object).isEmpty();
        }
        if (object instanceof Map<?, ?>) {
            return ((Map<?, ?>) object).isEmpty();
        }
        if (object instanceof Optional<?>) {
            // TODO Java 11 Use Optional#isEmpty()
            return !((Optional<?>) object).isPresent();
        }
        return false;
    }

    /**
     * Tests if an Object is not empty and not null.
     * <p>
     * The following types are supported:
     * </p>
     * <ul>
     * <li>{@link CharSequence}: Considered empty if its length is zero.</li>
     * <li>{@link Array}: Considered empty if its length is zero.</li>
     * <li>{@link Collection}: Considered empty if it has zero elements.</li>
     * <li>{@link Map}: Considered empty if it has zero key-value mappings.</li>
     * <li>{@link Optional}: Considered empty if {@link Optional#isPresent} returns false, regardless of the "emptiness" of the contents.</li>
     * </ul>
     *
     * <pre>
     * ObjectUtils.isNotEmpty(null)             = false
     * ObjectUtils.isNotEmpty("")               = false
     * ObjectUtils.isNotEmpty("ab")             = true
     * ObjectUtils.isNotEmpty(new int[]{})      = false
     * ObjectUtils.isNotEmpty(new int[]{1,2,3}) = true
     * ObjectUtils.isNotEmpty(1234)             = true
     * ObjectUtils.isNotEmpty(Optional.of(""))  = true
     * ObjectUtils.isNotEmpty(Optional.empty()) = false
     * </pre>
     *
     * @param object  the {@link Object} to test, may be {@code null}.
     * @return {@code true} if the object has an unsupported type or is not empty.
     * and not null, {@code false} otherwise.
     * @since 3.9
     */
    public static boolean isNotEmpty(final Object object) {
        return !isEmpty(object);
    }

    /**
     * Null safe comparison of Comparables.
     * <p>
     * TODO Move to ComparableUtils.
     * </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>
     */
    @SafeVarargs
    public static <T extends Comparable<? super T>> T max(final T... values) {
        T result = null;
        if (values != null) {
            for (final T value : values) {
                if (compare(value, result, false) > 0) {
                    result = value;
                }
            }
        }
        return result;
    }

    /**
     * Finds 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
     */
    @SafeVarargs
    public static <T> T median(final Comparator<T> comparator, final T... items) {
        Validate.notEmpty(items, "null/empty items");
        Validate.noNullElements(items);
        Objects.requireNonNull(comparator, "comparator");
        final TreeSet<T> treeSet = new TreeSet<>(comparator);
        Collections.addAll(treeSet, items);
        return (T) treeSet.toArray()[(treeSet.size() - 1) / 2];
    }

    /**
     * Finds 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
     */
    @SafeVarargs
    public static <T extends Comparable<? super T>> T median(final T... items) {
        Validate.notEmpty(items);
        Validate.noNullElements(items);
        final TreeSet<T> sort = new TreeSet<>();
        Collections.addAll(sort, items);
        return (T) sort.toArray()[(sort.size() - 1) / 2];
    }

    /**
     * Null safe comparison of Comparables.
     * <p>
     * TODO Move to ComparableUtils.
     * </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>
     */
    @SafeVarargs
    public static <T extends Comparable<? super T>> T min(final T... values) {
        T result = null;
        if (values != null) {
            for (final T value : values) {
                if (compare(value, result, true) < 0) {
                    result = value;
                }
            }
        }
        return result;
    }

    /**
     * Finds 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
     */
    @SafeVarargs
    public static <T> T mode(final T... items) {
        if (ArrayUtils.isNotEmpty(items)) {
            final HashMap<T, MutableInt> occurrences = new HashMap<>(items.length);
            for (final T t : items) {
                ArrayUtils.increment(occurrences, t);
            }
            T result = null;
            int max = 0;
            for (final Map.Entry<T, MutableInt> e : occurrences.entrySet()) {
                final int cmp = e.getValue().intValue();
                if (cmp == max) {
                    result = null;
                } else if (cmp > max) {
                    max = cmp;
                    result = e.getKey();
                }
            }
            return result;
        }
        return null;
    }

    /**
     * Compares two objects for inequality, where either one or both
     * objects may be {@code null}.
     *
     * <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(final Object object1, final Object object2) {
        return !Objects.equals(object1, object2);
    }

    /**
     * Checks that the specified object reference is not {@code null} or empty per {@link #isEmpty(Object)}. Use this
     * method for validation, for example:
     *
     * <pre>
     * public Foo(Bar bar) {
     *     this.bar = Objects.requireNonEmpty(bar);
     * }
     * </pre>
     *
     * @param <T> the type of the reference.
     * @param obj the object reference to check for nullity.
     * @return {@code obj} if not {@code null}.
     * @throws NullPointerException     if {@code obj} is {@code null}.
     * @throws IllegalArgumentException if {@code obj} is empty per {@link #isEmpty(Object)}.
     * @see #isEmpty(Object)
     * @since 3.12.0
     */
    public static <T> T  requireNonEmpty(final T obj) {
        return requireNonEmpty(obj, "object");
    }

    /**
     * Checks that the specified object reference is not {@code null} or empty per {@link #isEmpty(Object)}. Use this
     * method for validation, for example:
     *
     * <pre>
     * public Foo(Bar bar) {
     *     this.bar = Objects.requireNonEmpty(bar, "bar");
     * }
     * </pre>
     *
     * @param <T> the type of the reference.
     * @param obj the object reference to check for nullity.
     * @param message the exception message.
     * @return {@code obj} if not {@code null}.
     * @throws NullPointerException     if {@code obj} is {@code null}.
     * @throws IllegalArgumentException if {@code obj} is empty per {@link #isEmpty(Object)}.
     * @see #isEmpty(Object)
     * @since 3.12.0
     */
    public static <T> T requireNonEmpty(final T obj, final String message) {
        // check for null first to give the most precise exception.
        Objects.requireNonNull(obj, message);
        if (isEmpty(obj)) {
            throw new IllegalArgumentException(message);
        }
        return obj;
    }

    /**
     * Gets the {@code toString()} of an {@link Object} or the empty string ({@code ""}) if the input is {@code null}.
     *
     * <pre>
     * ObjectUtils.toString(null)         = ""
     * ObjectUtils.toString("")           = ""
     * ObjectUtils.toString("bat")        = "bat"
     * ObjectUtils.toString(Boolean.TRUE) = "true"
     * </pre>
     *
     * @param obj  the Object to {@code toString()}, may be {@code null}.
     * @return the input's {@code toString()}, or {@code ""} if the input is {@code null}.
     * @see Objects#toString(Object)
     * @see Objects#toString(Object, String)
     * @see StringUtils#defaultString(String)
     * @see String#valueOf(Object)
     * @since 2.0
     */
    public static String toString(final Object obj) {
        return Objects.toString(obj, StringUtils.EMPTY);
    }

    /**
     * Gets the {@code toString} of an {@link Object} returning
     * a specified text if {@code null} input.
     *
     * <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>
     *
     * @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 {@code nullStr} if {@code null} input.
     * @see Objects#toString(Object)
     * @see Objects#toString(Object, String)
     * @see StringUtils#defaultString(String,String)
     * @see String#valueOf(Object)
     * @since 2.0
     * @deprecated this method has been replaced by {@code java.util.Objects.toString(Object, String)} in Java 7 and
     * will be removed in future releases.
     */
    @Deprecated
    public static String toString(final Object obj, final String nullStr) {
        return Objects.toString(obj, nullStr);
    }

    /**
     * Gets the {@code toString} of an {@link Supplier}'s {@link Supplier#get()} returning
     * a specified text if {@code null} input.
     *
     * <pre>{@code
     * ObjectUtils.toString(() -> obj, () -> expensive())
     * </pre>
     * <pre>
     * ObjectUtils.toString(() -> null, () -> expensive())         = result of expensive()
     * ObjectUtils.toString(() -> null, () -> expensive())         = result of expensive()
     * ObjectUtils.toString(() -> "", () -> expensive())           = ""
     * ObjectUtils.toString(() -> "bat", () -> expensive())        = "bat"
     * ObjectUtils.toString(() -> Boolean.TRUE, () -> expensive()) = "true"
     * }</pre>
     *
     * @param obj  the Object to {@code toString}, may be null.
     * @param supplier  the Supplier of String used on {@code null} input, may be null.
     * @return the passed in Object's toString, or {@code nullStr} if {@code null} input.
     * @since 3.14.0
     */
    public static String toString(final Supplier<Object> obj, final Supplier<String> supplier) {
        return obj == null ? Suppliers.get(supplier) : toString(obj.get(), supplier);
    }

    /**
     * Gets the {@code toString} of an {@link Object} returning
     * a specified text if {@code null} input.
     *
     * <pre>{@code
     * ObjectUtils.toString(obj, () -> expensive())
     * }</pre>
     * <pre>{@code
     * ObjectUtils.toString(null, () -> expensive())         = result of expensive()
     * ObjectUtils.toString(null, () -> expensive())         = result of expensive()
     * ObjectUtils.toString("", () -> expensive())           = ""
     * ObjectUtils.toString("bat", () -> expensive())        = "bat"
     * ObjectUtils.toString(Boolean.TRUE, () -> expensive()) = "true"
     * }</pre>
     *
     * @param <T> the obj type (used to provide better source compatibility in 3.14.0).
     * @param obj  the Object to {@code toString}, may be null.
     * @param supplier  the Supplier of String used on {@code null} input, may be null.
     * @return the passed in Object's toString, or {@code nullStr} if {@code null} input.
     * @since 3.11
     */
    public static <T> String toString(final T obj, final Supplier<String> supplier) {
        return obj == null ? Suppliers.get(supplier) : obj.toString();
    }

    /**
     * Calls {@link Object#wait(long, int)} for the given Duration.
     *
     * @param obj The receiver of the wait call.
     * @param duration How long to wait.
     * @throws IllegalArgumentException if the timeout duration is negative.
     * @throws IllegalMonitorStateException if the current thread is not the owner of the {@code obj}'s monitor.
     * @throws InterruptedException if any thread interrupted the current thread before or while the current thread was
     *         waiting for a notification. The <em>interrupted status</em> of the current thread is cleared when this
     *         exception is thrown.
     * @see Object#wait(long, int)
     * @since 3.12.0
     */
    public static void wait(final Object obj, final Duration duration) throws InterruptedException {
        DurationUtils.accept(obj::wait, DurationUtils.zeroIfNull(duration));
    }

    /**
     * {@link 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>
     * This constructor is public to permit tools that require a JavaBean instance to operate.
     * </p>
     *
     * @deprecated TODO Make private in 4.0.
     */
    @Deprecated
    public ObjectUtils() {
        // empty
    }

}