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.
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.
a
- an objectb
- an object to be compared with a
for equalitytrue
if the arguments are equal to each other and false
otherwiseObject.equals(Object)
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.
a
- an objectb
- an object to be compared with a
for deep equalitytrue
if the arguments are deeply equal to each other and false
otherwiseArrays.deepEquals(Object[], Object[])
, equals(Object, Object)
public static int hashCode(Object o)
Returns the hash code of a non-null
argument and 0 for a null
argument.
o
- an objectnull
argument and 0 for a null
argumentObject.hashCode()
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)
.values
- the values to be hashedArrays.hashCode(Object[])
, List.hashCode()
public static String toString(Object o)
Returns the result of calling toString
for a non-null
argument and "null"
for a null
argument.
o
- an objecttoString
for a non-null
argument and "null"
for a null
argumentObject.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.
o
- an objectnullDefault
- string to return if the first argument is null
toString
on the first argument if it is not null
and the second argument otherwise.toString(Object)
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.
T
- the type of the objects being compareda
- an objectb
- an object to be compared with a
c
- the Comparator
to compare the first two argumentsc.compare(a, b)
otherwise.Comparable
, Comparator
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); }
T
- the type of the referenceobj
- the object reference to check for nullityobj
if not null
NullPointerException
- if obj
is null
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"); }
T
- the type of the referenceobj
- the object reference to check for nullitymessage
- detail message to be used in the event that a NullPointerException
is thrownobj
if not null
NullPointerException
- if obj
is null
public static boolean isNull(Object obj)
Returns true
if the provided reference is null
otherwise returns false
.
Predicate
, filter(Objects::isNull)
obj
- a reference to be checked against null
true
if the provided reference is null
otherwise false
Predicate
public static boolean nonNull(Object obj)
Returns true
if the provided reference is non-null
otherwise returns false
.
Predicate
, filter(Objects::nonNull)
obj
- a reference to be checked against null
true
if the provided reference is non-null
otherwise false
Predicate
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.
T
- the type of the referenceobj
- the object reference to check for nullitymessageSupplier
- supplier of the detail message to be used in the event that a NullPointerException
is thrownobj
if not null
NullPointerException
- if obj
is null
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