Indicates whether some other object is “equal to” this one.
The equals
method implements an equivalence relation
on non-null object references:
- It is reflexive: for any non-null reference value
x
,x.equals(x)
should return
true
. - It is symmetric: for any non-null reference values
x
andy
,x.equals(y)
should returntrue
if and only if
y.equals(x)
returnstrue
. - It is transitive: for any non-null reference values
x
,y
, andz
, if
x.equals(y)
returnstrue
and
y.equals(z)
returnstrue
, then
x.equals(z)
should returntrue
. - It is consistent: for any non-null reference values
x
andy
, multiple invocations of
x.equals(y)
consistently returntrue
or consistently returnfalse
, provided no
information used inequals
comparisons on the
objects is modified. - For any non-null reference value
x
,
x.equals(null)
should returnfalse
.
The equals
method for class Object
implements
the most discriminating possible equivalence relation on objects;
that is, for any non-null reference values x
and
y
, this method returns true
if and only
if x
and y
refer to the same object
(x == y
has the value true
).
Note that it is generally necessary to override the hashCode
method whenever this method is overridden, so as to maintain the
general contract for the hashCode
method, which states
that equal objects must have equal hash codes.