Add java.util.Objects

Author: peterschrammel

src/main/java/java/util/Objects.java

@@ -0,0 +1,298 @@
+/*
+ * Copyright (c) 2009, 2013, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * 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).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+import java.util.function.Supplier;
+
+/**
+ * This class consists of {@code static} utility methods for operating
+ * on objects.  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, and comparing two objects.
+ *
+ * @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>
+    * &#064;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}
+     *
+     * @diffblue.fullSupport
+     * @diffblue.untested
+     * We do not have tests for this method, but it is called from some tested
+     * modelled methods.
+     */
+    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;
+    }
+
+    /**
+     * 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;
+    }
+}