Objects (Java Platform SE 8 )
Keywords: java.util.Objects class
Date: 2015-05-24

compact1, compact2, compact3
java.util

## Class Objects

- java.lang.Object
- - java.util.Objects

-     public final class Objects
      extends Object

  This class consists of `static` utility methods for operating on objects. These utilities include `null`-safe or `null`-tolerant methods for computing the hash code of an object, returning a string for an object, and comparing two objects.
  Since:
    1.7

- - ### Method Summary

    All Methods Static Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static <T> int` | `compare(T a, T b, Comparator<? super T> c)` Returns 0 if the arguments are identical and `c.compare(a, b)` otherwise.
    `static boolean` | `deepEquals(Object a, Object b)` Returns `true` if the arguments are deeply equal to each other and `false` otherwise.
    `static boolean` | `equals(Object a, Object b)` Returns `true` if the arguments are equal to each other and `false` otherwise.
    `static int` | `hash(Object... values)` Generates a hash code for a sequence of input values.
    `static int` | `hashCode(Object o)` Returns the hash code of a non-`null` argument and 0 for a `null` argument.
    `static boolean` | `isNull(Object obj)` Returns `true` if the provided reference is `null` otherwise returns `false`.
    `static boolean` | `nonNull(Object obj)` Returns `true` if the provided reference is non-`null` otherwise returns `false`.
    `static <T> T` | `requireNonNull(T obj)` Checks that the specified object reference is not `null`.
    `static <T> T` | `requireNonNull(T obj, String message)` Checks that the specified object reference is not `null` and throws a customized `NullPointerException` if it is.
    `static <T> T` | `requireNonNull(T obj, Supplier<String> messageSupplier)` Checks that the specified object reference is not `null` and throws a customized `NullPointerException` if it is.
    `static String` | `toString(Object o)` Returns the result of calling `toString` for a non-`null` argument and `"null"` for a `null` argument.
    `static String` | `toString(Object o, String nullDefault)` Returns the result of calling `toString` on the first argument if the first argument is not `null` and returns the second argument otherwise.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Method Detail

    - #### equals

          public static boolean equals(Object a,
                                       Object b)

      Returns `true` if the arguments are equal to each other and `false` otherwise. Consequently, if both arguments are `null`, `true` is returned and if exactly one argument is `null`, `false` is returned. Otherwise, equality is determined by using the `equals` method of the first argument.
      Parameters:
        `a` - an object
        `b` - an object to be compared with `a` for equality
      Returns:
        `true` if the arguments are equal to each other and `false` otherwise
      See Also:
        `Object.equals(Object)`

    - #### deepEquals

          public static boolean deepEquals(Object a,
                                           Object b)

      Returns `true` if the arguments are deeply equal to each other and `false` otherwise. Two `null` values are deeply equal. If both arguments are arrays, the algorithm in `Arrays.deepEquals` is used to determine equality. Otherwise, equality is determined by using the `equals` method of the first argument.
      Parameters:
        `a` - an object
        `b` - an object to be compared with `a` for deep equality
      Returns:
        `true` if the arguments are deeply equal to each other and `false` otherwise
      See Also:
        `Arrays.deepEquals(Object[], Object[])`, `equals(Object, Object)`

    - #### hashCode

          public static int hashCode(Object o)

      Returns the hash code of a non-`null` argument and 0 for a `null` argument.
      Parameters:
        `o` - an object
      Returns:
        the hash code of a non-`null` argument and 0 for a `null` argument
      See Also:
        `Object.hashCode()`

    - #### hash

          public static int hash(Object... values)

      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 `Arrays.hashCode(Object[])`.

      This method is useful for implementing `Object.hashCode()` on objects containing multiple fields. For example, if an object that has three fields, `x`, `y`, and `z`, one could write:

      >      @Override public int hashCode() {
      >          return Objects.hash(x, y, z);
      >      }

      Warning: When a single object reference is supplied, the returned value does not equal the hash code of that object reference. This value can be computed by calling `hashCode(Object)`.
      Parameters:
        `values` - the values to be hashed
      Returns:
        a hash value of the sequence of input values
      See Also:
        `Arrays.hashCode(Object[])`, `List.hashCode()`

    - #### toString

          public static String toString(Object o)

      Returns the result of calling `toString` for a non-`null` argument and `"null"` for a `null` argument.
      Parameters:
        `o` - an object
      Returns:
        the result of calling `toString` for a non-`null` argument and `"null"` for a `null` argument
      See Also:
        `Object.toString()`, `String.valueOf(Object)`

    - #### toString

          public static String toString(Object o,
                                        String nullDefault)

      Returns the result of calling `toString` on the first argument if the first argument is not `null` and returns the second argument otherwise.
      Parameters:
        `o` - an object
        `nullDefault` - string to return if the first argument is `null`
      Returns:
        the result of calling `toString` on the first argument if it is not `null` and the second argument otherwise.
      See Also:
        `toString(Object)`

    - #### compare

          public static <T> int compare(T a,
                                        T b,
                                        Comparator<? super T> c)

      Returns 0 if the arguments are identical and `c.compare(a, b)` otherwise. Consequently, if both arguments are `null` 0 is returned.

      Note that if one of the arguments is `null`, a `NullPointerException` may or may not be thrown depending on what ordering policy, if any, the `Comparator` chooses to have for `null` values.

      Type Parameters:
        `T` - the type of the objects being compared
      Parameters:
        `a` - an object
        `b` - an object to be compared with `a`
        `c` - the `Comparator` to compare the first two arguments
      Returns:
        0 if the arguments are identical and `c.compare(a, b)` otherwise.
      See Also:
        `Comparable`, `Comparator`

    - #### requireNonNull

          public static <T> T requireNonNull(T obj)

      Checks that the specified object reference is not `null`. This method is designed primarily for doing parameter validation in methods and constructors, as demonstrated below:

      >      public Foo(Bar bar) {
      >          this.bar = Objects.requireNonNull(bar);
      >      }

      Type Parameters:
        `T` - the type of the reference
      Parameters:
        `obj` - the object reference to check for nullity
      Returns:
        `obj` if not `null`
      Throws:
        `NullPointerException` - if `obj` is `null`

    - #### requireNonNull

          public static <T> T requireNonNull(T obj,
                                             String message)

      Checks that the specified object reference is not `null` and throws a customized `NullPointerException` if it is. This method is designed primarily for doing parameter validation in methods and constructors with multiple parameters, as demonstrated below:

      >      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");
      >      }

      Type Parameters:
        `T` - the type of the reference
      Parameters:
        `obj` - the object reference to check for nullity
        `message` - detail message to be used in the event that a `NullPointerException` is thrown
      Returns:
        `obj` if not `null`
      Throws:
        `NullPointerException` - if `obj` is `null`

    - #### isNull

          public static boolean isNull(Object obj)

      Returns `true` if the provided reference is `null` otherwise returns `false`.
      API Note:
        This method exists to be used as a `Predicate`, `filter(Objects::isNull)`
      Parameters:
        `obj` - a reference to be checked against `null`
      Returns:
        `true` if the provided reference is `null` otherwise `false`
      Since:
        1.8
      See Also:
        `Predicate`

    - #### nonNull

          public static boolean nonNull(Object obj)

      Returns `true` if the provided reference is non-`null` otherwise returns `false`.
      API Note:
        This method exists to be used as a `Predicate`, `filter(Objects::nonNull)`
      Parameters:
        `obj` - a reference to be checked against `null`
      Returns:
        `true` if the provided reference is non-`null` otherwise `false`
      Since:
        1.8
      See Also:
        `Predicate`

    - #### requireNonNull

          public static <T> T requireNonNull(T obj,
                                             Supplier<String> messageSupplier)

      Checks that the specified object reference is not `null` and throws a customized `NullPointerException` if it is.

      Unlike the method `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.

      Type Parameters:
        `T` - the type of the reference
      Parameters:
        `obj` - the object reference to check for nullity
        `messageSupplier` - supplier of the detail message to be used in the event that a `NullPointerException` is thrown
      Returns:
        `obj` if not `null`
      Throws:
        `NullPointerException` - if `obj` is `null`
      Since:
        1.8

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