Objects

AI-generated Key Takeaways

• The Objects class provides static utility methods for performing common operations on objects, such as null checks, comparisons, and hash code generation.

• It offers null-safe alternatives to standard methods, helping to prevent NullPointerExceptions and improve code robustness.

• The class includes methods for deep equality checks, comparing objects using Comparators, and generating hash codes for multiple fields.

• It provides convenient ways to handle null values, including methods for checking, requiring non-null values, and providing default values.

• The Objects class simplifies object manipulation and enhances code clarity by offering concise and reliable utility functions.

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.

Public Method Summary

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, 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	requireNonNull(T obj) Checks that the specified object reference is not null.
static <T> T	requireNonNullElse(T obj, T defaultObj) Returns the first argument if it is non-null and otherwise returns the non-null second argument.
static <T> T	requireNonNullElseGet(T obj, Supplier<? extends T> supplier) Returns the first argument if it is non-null and otherwise returns the non-null value of supplier.get().
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.

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Methods

public static 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.

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

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)

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)

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()

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()

public static boolean isNull (Object obj)

Returns true if the provided reference is null otherwise returns false.

Parameters

obj	a reference to be checked against null

Returns

• true if the provided reference is null otherwise false

See Also

• Predicate

public static boolean nonNull (Object obj)

Returns true if the provided reference is non-null otherwise returns false.

Parameters

obj	a reference to be checked against null

Returns

• true if the provided reference is non-null otherwise false

See Also

• Predicate

public static 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");
 }
 

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

public static 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.

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

public static 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);
 }
 

Parameters

obj	the object reference to check for nullity

Returns

• obj if not null

Throws

NullPointerException	if obj is null

public static T requireNonNullElse (T obj, T defaultObj)

Returns the first argument if it is non-null and otherwise returns the non-null second argument.

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

public static T requireNonNullElseGet (T obj, Supplier<? extends T> supplier)

Returns the first argument if it is non-null and otherwise returns the non-null value of supplier.get().

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

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)

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)