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Objects

public final class Objects
extends Object

java.lang.Object
   ↳ java.util.Objects


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.

Summary

Public methods

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 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 methods

From class java.lang.Object

Public methods

compare

Added in API level 19
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 T: an object
b T: an object to be compared with a
c Comparator: the Comparator to compare the first two arguments
Returns
int 0 if the arguments are identical and c.compare(a, b) otherwise.

See also:

deepEquals

Added in API level 19
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 Object: an object
b Object: an object to be compared with a for deep equality
Returns
boolean true if the arguments are deeply equal to each other and false otherwise

See also:

equals

Added in API level 19
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 Object: an object
b Object: an object to be compared with a for equality
Returns
boolean true if the arguments are equal to each other and false otherwise

See also:

hash

Added in API level 19
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 hashCode(Object[]).

This method is useful for implementing 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 Object: the values to be hashed
Returns
int a hash value of the sequence of input values

See also:

hashCode

Added in API level 19
int hashCode (Object o)

Returns the hash code of a non-null argument and 0 for a null argument.

Parameters
o Object: an object
Returns
int the hash code of a non-null argument and 0 for a null argument

See also:

isNull

Added in API level 24
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 Object: a reference to be checked against null
Returns
boolean true if the provided reference is null otherwise false

See also:

nonNull

Added in API level 24
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 Object: a reference to be checked against null
Returns
boolean true if the provided reference is non-null otherwise false

See also:

requireNonNull

Added in API level 19
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 T: the object reference to check for nullity
message String: detail message to be used in the event that a NullPointerException is thrown
Returns
T obj if not null
Throws
NullPointerException if obj is null

requireNonNull

Added in API level 24
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 T: the object reference to check for nullity
messageSupplier Supplier: supplier of the detail message to be used in the event that a NullPointerException is thrown
Returns
T obj if not null
Throws
NullPointerException if obj is null

requireNonNull

Added in API level 19
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 T: the object reference to check for nullity
Returns
T obj if not null
Throws
NullPointerException if obj is null

toString

Added in API level 19
String toString (Object o)

Returns the result of calling toString for a non-null argument and "null" for a null argument.

Parameters
o Object: an object
Returns
String the result of calling toString for a non-null argument and "null" for a null argument

See also:

toString

Added in API level 19
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 Object: an object
nullDefault String: string to return if the first argument is null
Returns
String the result of calling toString on the first argument if it is not null and the second argument otherwise.

See also:

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