# 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, or checking certain conditions before operation. These utilities include `null`-safe or `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.

Since:
  1.7

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static int`
  `checkFromIndexSize(int fromIndex, int size, int length)`
  Checks if the sub-range from `fromIndex` (inclusive) to `fromIndex + size` (exclusive) is within the bounds of range from `0` (inclusive) to `length` (exclusive).
  `static long`
  `checkFromIndexSize(long fromIndex, long size, long length)`
  Checks if the sub-range from `fromIndex` (inclusive) to `fromIndex + size` (exclusive) is within the bounds of range from `0` (inclusive) to `length` (exclusive).
  `static int`
  `checkFromToIndex(int fromIndex, int toIndex, int length)`
  Checks if the sub-range from `fromIndex` (inclusive) to `toIndex` (exclusive) is within the bounds of range from `0` (inclusive) to `length` (exclusive).
  `static long`
  `checkFromToIndex(long fromIndex, long toIndex, long length)`
  Checks if the sub-range from `fromIndex` (inclusive) to `toIndex` (exclusive) is within the bounds of range from `0` (inclusive) to `length` (exclusive).
  `static int`
  `checkIndex(int index, int length)`
  Checks if the `index` is within the bounds of the range from `0` (inclusive) to `length` (exclusive).
  `static long`
  `checkIndex(long index, long length)`
  Checks if the `index` is within the bounds of the range from `0` (inclusive) to `length` (exclusive).
  `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)`
  Returns 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`; `false` otherwise.
  `static boolean`
  `nonNull(Object obj)`
  Returns `true` if the provided reference is non-`null`; `false` otherwise.
  `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 <T> T`
  `requireNonNullElse(T obj, T defaultObj)`
  Returns the first argument if it is non-`null` and otherwise the second argument if it is non-`null`.
  `static <T> T`
  `requireNonNullElseGet(T obj, Supplier<? extends T> supplier)`
  Returns the first argument if it is non-`null` and otherwise the value from `supplier.get()` if it is non-`null`.
  `static String`
  `toIdentityString(Object o)`
  Returns a string equivalent to the string returned by `Object.toString` if that method and `hashCode` are not overridden.
  `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 the second argument otherwise.

  ### Methods declared in class java.lang.Object

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

- ## Method Details

  - ### 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. Otherwise, if the first argument is not `null`, equality is determined by calling the `equals` method of the first argument with the second argument of this method. Otherwise, `false` is returned.
    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)
    Returns 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 code for a 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 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 the first argument is not `null` and the second argument otherwise
    See Also:
      - `toString(Object)`

  - ### toIdentityString

    public static String toIdentityString(Object o)
    Returns a string equivalent to the string returned by `Object.toString` if that method and `hashCode` are not overridden.
    Implementation Requirements:
      The method returns a string equivalent to:
      `o.getClass().getName() + "@" + Integer.toHexString(System.identityHashCode(o))`
    Implementation Note:
      This method constructs a string for an object without calling any overridable methods of the object.
    Parameters:
      `o` - an object
    Returns:
      a string equivalent to the string returned by `Object.toString` if that method and `hashCode` are not overridden
    Throws:
      `NullPointerException` - if the argument is null
    Since:
      19
    See Also:
      - `Object.toString()`
      - `System.identityHashCode(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`; `false` otherwise.
    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`; `false` otherwise
    Since:
      1.8
    See Also:
      - `Predicate`

  - ### nonNull

    public static boolean nonNull(Object obj)
    Returns `true` if the provided reference is non-`null`; `false` otherwise.
    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`; `false` otherwise
    Since:
      1.8
    See Also:
      - `Predicate`

  - ### requireNonNullElse

    public static <T> T requireNonNullElse(T obj, T defaultObj)
    Returns the first argument if it is non-`null` and otherwise the second argument if it is non-`null`.
    Type Parameters:
      `T` - the type of the reference
    Parameters:
      `obj` - an object
      `defaultObj` - a non-`null` object to return if the first argument is `null`
    Returns:
      the first argument if it is non-`null` and otherwise the second argument if it is non-`null`
    Throws:
      `NullPointerException` - if both `obj` is null and `defaultObj` is `null`
    Since:
      9

  - ### requireNonNullElseGet

    public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier)
    Returns the first argument if it is non-`null` and otherwise the value from `supplier.get()` if it is non-`null`.
    Type Parameters:
      `T` - the type of the first argument and return type
    Parameters:
      `obj` - an object
      `supplier` - of a non-`null` object to return if the first argument is `null`
    Returns:
      the first argument if it is non-`null` and otherwise the value from `supplier.get()` if it is non-`null`
    Throws:
      `NullPointerException` - if both `obj` is null and either the `supplier` is `null` or the `supplier.get()` value is `null`
    Since:
      9

  - ### 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

  - ### checkIndex

    public static int checkIndex(int index, int length)
    Checks if the `index` is within the bounds of the range from `0` (inclusive) to `length` (exclusive).

    The `index` is defined to be out of bounds if any of the following inequalities is true:

    - `index < 0`
    - `index >= length`
    - `length < 0`, which is implied from the former inequalities
    Parameters:
      `index` - the index
      `length` - the upper-bound (exclusive) of the range
    Returns:
      `index` if it is within bounds of the range
    Throws:
      `IndexOutOfBoundsException` - if the `index` is out of bounds
    Since:
      9

  - ### checkFromToIndex

    public static int checkFromToIndex(int fromIndex, int toIndex, int length)
    Checks if the sub-range from `fromIndex` (inclusive) to `toIndex` (exclusive) is within the bounds of range from `0` (inclusive) to `length` (exclusive).

    The sub-range is defined to be out of bounds if any of the following inequalities is true:

    - `fromIndex < 0`
    - `fromIndex > toIndex`
    - `toIndex > length`
    - `length < 0`, which is implied from the former inequalities
    Parameters:
      `fromIndex` - the lower-bound (inclusive) of the sub-range
      `toIndex` - the upper-bound (exclusive) of the sub-range
      `length` - the upper-bound (exclusive) the range
    Returns:
      `fromIndex` if the sub-range within bounds of the range
    Throws:
      `IndexOutOfBoundsException` - if the sub-range is out of bounds
    Since:
      9

  - ### checkFromIndexSize

    public static int checkFromIndexSize(int fromIndex, int size, int length)
    Checks if the sub-range from `fromIndex` (inclusive) to `fromIndex + size` (exclusive) is within the bounds of range from `0` (inclusive) to `length` (exclusive).

    The sub-range is defined to be out of bounds if any of the following inequalities is true:

    - `fromIndex < 0`
    - `size < 0`
    - `fromIndex + size > length`, taking into account integer overflow
    - `length < 0`, which is implied from the former inequalities
    Parameters:
      `fromIndex` - the lower-bound (inclusive) of the sub-interval
      `size` - the size of the sub-range
      `length` - the upper-bound (exclusive) of the range
    Returns:
      `fromIndex` if the sub-range within bounds of the range
    Throws:
      `IndexOutOfBoundsException` - if the sub-range is out of bounds
    Since:
      9

  - ### checkIndex

    public static long checkIndex(long index, long length)
    Checks if the `index` is within the bounds of the range from `0` (inclusive) to `length` (exclusive).

    The `index` is defined to be out of bounds if any of the following inequalities is true:

    - `index < 0`
    - `index >= length`
    - `length < 0`, which is implied from the former inequalities
    Parameters:
      `index` - the index
      `length` - the upper-bound (exclusive) of the range
    Returns:
      `index` if it is within bounds of the range
    Throws:
      `IndexOutOfBoundsException` - if the `index` is out of bounds
    Since:
      16

  - ### checkFromToIndex

    public static long checkFromToIndex(long fromIndex, long toIndex, long length)
    Checks if the sub-range from `fromIndex` (inclusive) to `toIndex` (exclusive) is within the bounds of range from `0` (inclusive) to `length` (exclusive).

    The sub-range is defined to be out of bounds if any of the following inequalities is true:

    - `fromIndex < 0`
    - `fromIndex > toIndex`
    - `toIndex > length`
    - `length < 0`, which is implied from the former inequalities
    Parameters:
      `fromIndex` - the lower-bound (inclusive) of the sub-range
      `toIndex` - the upper-bound (exclusive) of the sub-range
      `length` - the upper-bound (exclusive) the range
    Returns:
      `fromIndex` if the sub-range within bounds of the range
    Throws:
      `IndexOutOfBoundsException` - if the sub-range is out of bounds
    Since:
      16

  - ### checkFromIndexSize

    public static long checkFromIndexSize(long fromIndex, long size, long length)
    Checks if the sub-range from `fromIndex` (inclusive) to `fromIndex + size` (exclusive) is within the bounds of range from `0` (inclusive) to `length` (exclusive).

    The sub-range is defined to be out of bounds if any of the following inequalities is true:

    - `fromIndex < 0`
    - `size < 0`
    - `fromIndex + size > length`, taking into account integer overflow
    - `length < 0`, which is implied from the former inequalities
    Parameters:
      `fromIndex` - the lower-bound (inclusive) of the sub-interval
      `size` - the size of the sub-range
      `length` - the upper-bound (exclusive) of the range
    Returns:
      `fromIndex` if the sub-range within bounds of the range
    Throws:
      `IndexOutOfBoundsException` - if the sub-range is out of bounds
    Since:
      16