public final class Objects extends Object
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.| Modifier and Type | Method and Description |
|---|---|
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 <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 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. |
public static <T> int compare(T a,
T b,
Comparator<? super T> c)
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 ac - the Comparator to compare the first two argumentsc.compare(a, b) otherwise.Comparable,
Comparatorpublic static boolean deepEquals(Object a, Object b)
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 boolean equals(Object a, Object b)
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 int hash(Object... values)
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);
}
hashCode(Object).values - the values to be hashedArrays.hashCode(Object[]),
List.hashCode()public static int hashCode(Object o)
null argument and 0 for
a null argument.o - an objectnull argument and 0 for
a null argumentObject.hashCode()public static <T> T requireNonNull(T obj)
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 nullNullPointerException - if obj is nullpublic static <T> T requireNonNull(T obj,
String message)
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 nullNullPointerException - if obj is nullpublic static String toString(Object o)
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)
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
nulltoString on the first
argument if it is not null and the second argument
otherwise.toString(Object)