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.
- API Note:
- Static methods such as
checkIndex(int, int)
,checkFromToIndex(int, int, int)
, andcheckFromIndexSize(int, int, int)
are provided for the convenience of checking if values corresponding to indexes and sub-ranges are out of bounds. Variations of these static methods support customization of the runtime exception, and corresponding exception detail message, that is thrown when values are out of bounds. Such methods accept a functional interface argument, instances ofBiFunction
, that maps out-of-bound values to a runtime exception. Care should be taken when using such methods in combination with an argument that is a lambda expression, method reference or class that capture values. In such cases the cost of capture, related to functional interface allocation, may exceed the cost of checking 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 |
static int | checkFromToIndex(int fromIndex,
int toIndex,
int length) | Checks if the sub-range from |
static int | checkIndex(int index,
int length) | Checks if the |
static <T> int | compare(T a,
T b,
Comparator<? super T> c) | Returns 0 if the arguments are identical and |
static boolean | deepEquals(Object a,
Object b) | Returns |
static boolean | equals(Object a,
Object b) | Returns |
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- |
static boolean | isNull(Object obj) | Returns |
static boolean | nonNull(Object obj) | Returns |
static <T> T | requireNonNull(T obj) | Checks that the specified object reference is not |
static <T> T | requireNonNull(T obj,
String message) | Checks that the specified object reference is not |
static <T> T | requireNonNull(T obj,
Supplier<String> messageSupplier) | Checks that the specified object reference is not |
static <T> T | requireNonNullElse(T obj,
T defaultObj) | Returns the first argument if it is non- |
static <T> T | requireNonNullElseGet(T obj,
Supplier<? extends T> supplier) | Returns the first argument if it is non- |
static String | toString(Object o) | Returns the result of calling |
static String | toString(Object o,
String nullDefault) | Returns the result of calling |
Methods declared in 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 witha
for equality - Returns:
-
true
if the arguments are equal to each other andfalse
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 witha
for deep equality - Returns:
-
true
if the arguments are deeply equal to each other andfalse
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 anull
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 anull
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 isnull
- Returns:
- the result of calling
toString
on the first argument if it is notnull
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 witha
-
c
- theComparator
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 notnull
- Throws:
-
NullPointerException
- ifobj
isnull
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 aNullPointerException
is thrown - Returns:
-
obj
if notnull
- Throws:
-
NullPointerException
- ifobj
isnull
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 againstnull
- Returns:
-
true
if the provided reference isnull
otherwisefalse
- 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 againstnull
- Returns:
-
true
if the provided reference is non-null
otherwisefalse
- 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 returns the non-null
second argument.
- Type Parameters:
-
T
- the type of the reference - Parameters:
-
obj
- an object -
defaultObj
- a non-null
object to return if the first argument isnull
- Returns:
- the first argument if it is non-
null
and otherwise the second argument if it is non-null
- Throws:
-
NullPointerException
- if bothobj
is null anddefaultObj
isnull
- 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 returns the non-null
value of supplier.get()
.
- 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 isnull
- Returns:
- the first argument if it is non-
null
and otherwise the value fromsupplier.get()
if it is non-null
- Throws:
-
NullPointerException
- if bothobj
is null and either thesupplier
isnull
or thesupplier.get()
value isnull
- 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 aNullPointerException
is thrown - Returns:
-
obj
if notnull
- Throws:
-
NullPointerException
- ifobj
isnull
- 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 theindex
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