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.
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 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 int checkIndex(int index, int 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)
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)
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 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.
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, waitReturns
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.
a - an object
b - an object to be compared with a for equality
true if the arguments are equal to each other and false otherwise
Object.equals(Object)
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 object
b - an object to be compared with a for deep equality
true if the arguments are deeply equal to each other and false otherwise
Arrays.deepEquals(Object[], Object[]), equals(Object, Object)
(
Object o)Returns the hash code of a non-null argument and 0 for a null argument.
o - an object
null argument and 0 for a null argument
Object.hashCode()
(
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 hashed
Arrays.hashCode(Object[]), List.hashCode()
Returns the result of calling toString for a non- null argument and "null" for a null argument.
o - an object
toString for a non- null argument and "null" for a null argument
Object.toString(), String.valueOf(Object)
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 object
nullDefault - 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)
(
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 compared
a - an object
b - an object to be compared with a
c - the Comparator to compare the first two arguments
c.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 reference
obj - the object reference to check for nullity
obj if not null
NullPointerException - if obj is null
(
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 reference
obj - the object reference to check for nullity
message - detail message to be used in the event that a NullPointerException is thrown
obj if not null
NullPointerException - if obj is null
(
Object obj)Returns true if the provided reference is null otherwise returns false.
(
Object obj)Returns true if the provided reference is non-null otherwise returns false.
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.
T - the type of the reference
obj - an object
defaultObj - a non-null object to return if the first argument is null
null and otherwise the second argument if it is non-null
NullPointerException - if both obj is null and defaultObj is null
(
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().
T - the type of the first argument and return type
obj - an object
supplier - of a non-null object to return if the first argument is null
null and otherwise the value from supplier.get() if it is non-null
NullPointerException - if both obj is null and either the supplier is null or the supplier.get() value is null
(
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 reference
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
obj if not null
NullPointerException - if obj is null
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 < 0index >= lengthlength < 0, which is implied from the former inequalitiesindex - the index
length - the upper-bound (exclusive) of the range
index if it is within bounds of the range
IndexOutOfBoundsException - if the index is out of bounds
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 < 0fromIndex > toIndextoIndex > lengthlength < 0, which is implied from the former inequalitiesfromIndex - the lower-bound (inclusive) of the sub-range
toIndex - the upper-bound (exclusive) of the sub-range
length - the upper-bound (exclusive) the range
fromIndex if the sub-range within bounds of the range
IndexOutOfBoundsException - if the sub-range is out of bounds
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 < 0size < 0fromIndex + size > length, taking into account integer overflowlength < 0, which is implied from the former inequalitiesfromIndex - the lower-bound (inclusive) of the sub-interval
size - the size of the sub-range
length - the upper-bound (exclusive) of the range
fromIndex if the sub-range within bounds of the range
IndexOutOfBoundsException - if the sub-range is out of bounds
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