Java Reference
In-Depth Information
Display 4.7
A Class with Methods
equals
and
toString
(part 2 of 2)
20
public boolean
precedes(DateFourthTry otherDate)
21
{
22
return
( (year < otherDate.year) ||
(year == otherDate.year && getMonth() <
otherDate.getMonth()) ||
24
(year == otherDate.year && month.equals(otherDate.month)
25
&& day < otherDate.day) );
26
}
<The rest of the method definitions are identical to the ones in
DateThirdTry
in Display 4.4 .>
27 }
The
return
statement in the definition of the method
precedes
may look
intimidating, but it is really straightforward. It says that
date1.precedes(date2)
returns
true
, provided one of the following three conditions is satisfied:
date1.year < date2.year
date1.year equals date2.year and date1.month comes before
date2.month date1 and date2 have the same year and month and
date1.day < date2.day.
If you give it a bit of thought, you will realize that
date1
precedes
date2
in time
precisely when one of these three conditions is satisfied.
The Methods
equals
and
toString
Java expects certain methods to be in all, or almost all, classes. This is because some
of the standard Java libraries have software that assumes such methods are defined.
Two of these methods are
equals
and
toString
. Therefore, you should include such
methods and be certain to spell their names exactly as we have done. Use
equals
, not
same
or
areEqual
. Do not even use
equal
without the
s
. Similar remarks apply to
the
toString
method. After we have developed more material, we will explain this in
more detail. In particular, we will then explain how to give a better method definition
for
equals
. For now, just get in the habit of including these methods.
The method
equals
is a
boolean
valued method to compare two objects of the class
to see if they satisfy the intuitive notion of “being equal.” So, the heading should be
equals
public boolean
equals(
Class_Name Parameter_Name
)
Display 4.7 contains definitions of the methods
equals
and
toString
that we might
add to our date class, which is now named
DateFourthTry
. The heading of that
equals
method is
public boolean
equals(DateFourthTry otherDate)
