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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package java.util;
import jdk.internal.util.Preconditions;
import jdk.internal.vm.annotation.ForceInline;
import java.util.function.Supplier;
/**
* This class consists of {@code static} utility methods for operating
* on objects, or checking certain conditions before operation. These utilities
* include {@code null}-safe or {@code null}-tolerant methods for computing the
* hash code of an object, returning a string for an object, comparing two
* objects, and checking if indexes or sub-range values are out-of-bounds.
*
* @apiNote
* Static methods such as {@link Objects#checkIndex},
* {@link Objects#checkFromToIndex}, and {@link Objects#checkFromIndexSize} are
* provided for the convenience of checking if values corresponding to indexes
* and sub-ranges are out-of-bounds.
* Variations of these static methods support customization of the runtime
* exception, and corresponding exception detail message, that is thrown when
* values are out-of-bounds. Such methods accept a functional interface
* argument, instances of {@code BiFunction}, that maps out-of-bound values to a
* runtime exception. Care should be taken when using such methods in
* combination with an argument that is a lambda expression, method reference or
* class that capture values. In such cases the cost of capture, related to
* functional interface allocation, may exceed the cost of checking bounds.
*
* @since 1.7
*/
public final class Objects {
private Objects() {
throw new AssertionError("No java.util.Objects instances for you!");
}
/**
* Returns {@code true} if the arguments are equal to each other
* and {@code false} otherwise.
* Consequently, if both arguments are {@code null}, {@code true}
* is returned and if exactly one argument is {@code null}, {@code
* false} is returned. Otherwise, equality is determined by using
* the {@link Object#equals equals} method of the first
* argument.
*
* @param a an object
* @param b an object to be compared with {@code a} for equality
* @return {@code true} if the arguments are equal to each other
* and {@code false} otherwise
* @see Object#equals(Object)
*/
public static boolean equals(Object a, Object b) {
return (a == b) || (a != null && a.equals(b));
}
/**
* Returns {@code true} if the arguments are deeply equal to each other
* and {@code false} otherwise.
*
* Two {@code null} values are deeply equal. If both arguments are
* arrays, the algorithm in {@link Arrays#deepEquals(Object[],
* Object[]) Arrays.deepEquals} is used to determine equality.
* Otherwise, equality is determined by using the {@link
* Object#equals equals} method of the first argument.
*
* @param a an object
* @param b an object to be compared with {@code a} for deep equality
* @return {@code true} if the arguments are deeply equal to each other
* and {@code false} otherwise
* @see Arrays#deepEquals(Object[], Object[])
* @see Objects#equals(Object, Object)
*/
public static boolean deepEquals(Object a, Object b) {
if (a == b)
return true;
else if (a == null || b == null)
return false;
else
return Arrays.deepEquals0(a, b);
}
/**
* Returns the hash code of a non-{@code null} argument and 0 for
* a {@code null} argument.
*
* @param o an object
* @return the hash code of a non-{@code null} argument and 0 for
* a {@code null} argument
* @see Object#hashCode
*/
public static int hashCode(Object o) {
return o != null ? o.hashCode() : 0;
}
/**
* Generates a hash code for a sequence of input values. The hash
* code is generated as if all the input values were placed into an
* array, and that array were hashed by calling {@link
* Arrays#hashCode(Object[])}.
*
* <p>This method is useful for implementing {@link
* Object#hashCode()} on objects containing multiple fields. For
* example, if an object that has three fields, {@code x}, {@code
* y}, and {@code z}, one could write:
*
* <blockquote><pre>
* @Override public int hashCode() {
* return Objects.hash(x, y, z);
* }
* </pre></blockquote>
*
* <b>Warning: When a single object reference is supplied, the returned
* value does not equal the hash code of that object reference.</b> This
* value can be computed by calling {@link #hashCode(Object)}.
*
* @param values the values to be hashed
* @return a hash value of the sequence of input values
* @see Arrays#hashCode(Object[])
* @see List#hashCode
*/
public static int hash(Object... values) {
return Arrays.hashCode(values);
}
/**
* Returns the result of calling {@code toString} for a non-{@code
* null} argument and {@code "null"} for a {@code null} argument.
*
* @param o an object
* @return the result of calling {@code toString} for a non-{@code
* null} argument and {@code "null"} for a {@code null} argument
* @see Object#toString
* @see String#valueOf(Object)
*/
public static String toString(Object o) {
return String.valueOf(o);
}
/**
* Returns the result of calling {@code toString} on the first
* argument if the first argument is not {@code null} and returns
* the second argument otherwise.
*
* @param o an object
* @param nullDefault string to return if the first argument is
* {@code null}
* @return the result of calling {@code toString} on the first
* argument if it is not {@code null} and the second argument
* otherwise.
* @see Objects#toString(Object)
*/
public static String toString(Object o, String nullDefault) {
return (o != null) ? o.toString() : nullDefault;
}
/**
* Returns 0 if the arguments are identical and {@code
* c.compare(a, b)} otherwise.
* Consequently, if both arguments are {@code null} 0
* is returned.
*
* <p>Note that if one of the arguments is {@code null}, a {@code
* NullPointerException} may or may not be thrown depending on
* what ordering policy, if any, the {@link Comparator Comparator}
* chooses to have for {@code null} values.
*
* @param <T> the type of the objects being compared
* @param a an object
* @param b an object to be compared with {@code a}
* @param c the {@code Comparator} to compare the first two arguments
* @return 0 if the arguments are identical and {@code
* c.compare(a, b)} otherwise.
* @see Comparable
* @see Comparator
*/
public static <T> int compare(T a, T b, Comparator<? super T> c) {
return (a == b) ? 0 : c.compare(a, b);
}
/**
* Checks that the specified object reference is not {@code null}. This
* method is designed primarily for doing parameter validation in methods
* and constructors, as demonstrated below:
* <blockquote><pre>
* public Foo(Bar bar) {
* this.bar = Objects.requireNonNull(bar);
* }
* </pre></blockquote>
*
* @param obj the object reference to check for nullity
* @param <T> the type of the reference
* @return {@code obj} if not {@code null}
* @throws NullPointerException if {@code obj} is {@code null}
*/
public static <T> T requireNonNull(T obj) {
if (obj == null)
throw new NullPointerException();
return obj;
}
/**
* Checks that the specified object reference is not {@code null} and
* throws a customized {@link NullPointerException} if it is. This method
* is designed primarily for doing parameter validation in methods and
* constructors with multiple parameters, as demonstrated below:
* <blockquote><pre>
* public Foo(Bar bar, Baz baz) {
* this.bar = Objects.requireNonNull(bar, "bar must not be null");
* this.baz = Objects.requireNonNull(baz, "baz must not be null");
* }
* </pre></blockquote>
*
* @param obj the object reference to check for nullity
* @param message detail message to be used in the event that a {@code
* NullPointerException} is thrown
* @param <T> the type of the reference
* @return {@code obj} if not {@code null}
* @throws NullPointerException if {@code obj} is {@code null}
*/
public static <T> T requireNonNull(T obj, String message) {
if (obj == null)
throw new NullPointerException(message);
return obj;
}
/**
* Returns {@code true} if the provided reference is {@code null} otherwise
* returns {@code false}.
*
* @apiNote This method exists to be used as a
* {@link java.util.function.Predicate}, {@code filter(Objects::isNull)}
*
* @param obj a reference to be checked against {@code null}
* @return {@code true} if the provided reference is {@code null} otherwise
* {@code false}
*
* @see java.util.function.Predicate
* @since 1.8
*/
public static boolean isNull(Object obj) {
return obj == null;
}
/**
* Returns {@code true} if the provided reference is non-{@code null}
* otherwise returns {@code false}.
*
* @apiNote This method exists to be used as a
* {@link java.util.function.Predicate}, {@code filter(Objects::nonNull)}
*
* @param obj a reference to be checked against {@code null}
* @return {@code true} if the provided reference is non-{@code null}
* otherwise {@code false}
*
* @see java.util.function.Predicate
* @since 1.8
*/
public static boolean nonNull(Object obj) {
return obj != null;
}
/**
* Returns the first argument if it is non-{@code null} and
* otherwise returns the non-{@code null} second argument.
*
* @param obj an object
* @param defaultObj a non-{@code null} object to return if the first argument
* is {@code null}
* @param <T> the type of the reference
* @return the first argument if it is non-{@code null} and
* otherwise the second argument if it is non-{@code null}
* @throws NullPointerException if both {@code obj} is null and
* {@code defaultObj} is {@code null}
* @since 9
*/
public static <T> T requireNonNullElse(T obj, T defaultObj) {
return (obj != null) ? obj : requireNonNull(defaultObj, "defaultObj");
}
/**
* Returns the first argument if it is non-{@code null} and otherwise
* returns the non-{@code null} value of {@code supplier.get()}.
*
* @param obj an object
* @param supplier of a non-{@code null} object to return if the first argument
* is {@code null}
* @param <T> the type of the first argument and return type
* @return the first argument if it is non-{@code null} and otherwise
* the value from {@code supplier.get()} if it is non-{@code null}
* @throws NullPointerException if both {@code obj} is null and
* either the {@code supplier} is {@code null} or
* the {@code supplier.get()} value is {@code null}
* @since 9
*/
public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier) {
return (obj != null) ? obj
: requireNonNull(requireNonNull(supplier, "supplier").get(), "supplier.get()");
}
/**
* Checks that the specified object reference is not {@code null} and
* throws a customized {@link NullPointerException} if it is.
*
* <p>Unlike the method {@link #requireNonNull(Object, String)},
* this method allows creation of the message to be deferred until
* after the null check is made. While this may confer a
* performance advantage in the non-null case, when deciding to
* call this method care should be taken that the costs of
* creating the message supplier are less than the cost of just
* creating the string message directly.
*
* @param obj the object reference to check for nullity
* @param messageSupplier supplier of the detail message to be
* used in the event that a {@code NullPointerException} is thrown
* @param <T> the type of the reference
* @return {@code obj} if not {@code null}
* @throws NullPointerException if {@code obj} is {@code null}
* @since 1.8
*/
public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
if (obj == null)
throw new NullPointerException(messageSupplier.get());
return obj;
}
/**
* Checks if the {@code index} is within the bounds of the range from
* {@code 0} (inclusive) to {@code length} (exclusive).
*
* <p>The {@code index} is defined to be out-of-bounds if any of the
* following inequalities is true:
* <ul>
* <li>{@code index < 0}</li>
* <li>{@code index >= length}</li>
* <li>{@code length < 0}, which is implied from the former inequalities</li>
* </ul>
*
* @param index the index
* @param length the upper-bound (exclusive) of the range
* @return {@code index} if it is within bounds of the range
* @throws IndexOutOfBoundsException if the {@code index} is out-of-bounds
* @since 9
*/
@ForceInline
public static
int checkIndex(int index, int length) {
return Preconditions.checkIndex(index, length, null);
}
/**
* Checks if the sub-range from {@code fromIndex} (inclusive) to
* {@code toIndex} (exclusive) is within the bounds of range from {@code 0}
* (inclusive) to {@code length} (exclusive).
*
* <p>The sub-range is defined to be out-of-bounds if any of the following
* inequalities is true:
* <ul>
* <li>{@code fromIndex < 0}</li>
* <li>{@code fromIndex > toIndex}</li>
* <li>{@code toIndex > length}</li>
* <li>{@code length < 0}, which is implied from the former inequalities</li>
* </ul>
*
* @param fromIndex the lower-bound (inclusive) of the sub-range
* @param toIndex the upper-bound (exclusive) of the sub-range
* @param length the upper-bound (exclusive) the range
* @return {@code fromIndex} if the sub-range within bounds of the range
* @throws IndexOutOfBoundsException if the sub-range is out-of-bounds
* @since 9
*/
public static
int checkFromToIndex(int fromIndex, int toIndex, int length) {
return Preconditions.checkFromToIndex(fromIndex, toIndex, length, null);
}
/**
* Checks if the sub-range from {@code fromIndex} (inclusive) to
* {@code fromIndex + size} (exclusive) is within the bounds of range from
* {@code 0} (inclusive) to {@code length} (exclusive).
*
* <p>The sub-range is defined to be out-of-bounds if any of the following
* inequalities is true:
* <ul>
* <li>{@code fromIndex < 0}</li>
* <li>{@code size < 0}</li>
* <li>{@code fromIndex + size > length}, taking into account integer overflow</li>
* <li>{@code length < 0}, which is implied from the former inequalities</li>
* </ul>
*
* @param fromIndex the lower-bound (inclusive) of the sub-interval
* @param size the size of the sub-range
* @param length the upper-bound (exclusive) of the range
* @return {@code fromIndex} if the sub-range within bounds of the range
* @throws IndexOutOfBoundsException if the sub-range is out-of-bounds
* @since 9
*/
public static
int checkFromIndexSize(int fromIndex, int size, int length) {
return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
}
}