Java Reference
In-Depth Information
Self-Test Exercises
1. Write a method called
makeItNewYears
that could be added to the class
DateFirstTry
in Display 4.1. The method
makeItNewYears
has no parameters
and sets the
month
instance variable to
"January"
and the
day
instance variable
to
1
. It does not change the
year
instance variable.
2. Write a method called
yellIfNewYear
that could be added to the class
DateFirstTry
in Display 4.1. The method
yellIfNewYear
has no parameters
and outputs the string
"Hurrah!"
provided the
month
instance variable has
the value
"January"
and the
day
instance variable has the value
1
. Otherwise,
it outputs the string
"Not New Year's Day."
More about Methods
As we noted for predefined methods, methods of the classes you define are of two kinds:
methods that return (compute) some value and methods that perform an action other
than returning a value. For example, the method
println
of the object
System.out
is an
example of a method that performs an action other than returning a value; in this case,
the action is to write something to the screen. The method
nextInt
of the class
Scanner
,
introduced in Chapter 2, is a method that returns a value; in this case, the value returned
is a number typed in by the user. A method that performs some action other than return-
ing a value is called a
void
method. This same distinction between
void
methods and
methods that return a value applies to methods in the classes you define. The two kinds
of methods require slight differences in how they are defined.
Both kinds of methods have a method heading and a method body, which are sim-
ilar but not identical for the two kinds of methods. The method heading for a
void
method is of the form
public void
Method_Name
(
Parameter_List
)
The method heading for a method that returns a value is
public
Type_Returned
Method_Name
(
Parameter_List
)
Later in the chapter we will see that
public
may sometimes be replaced by a more
restricted modifier and that it is possible to add additional modifiers, but these tem-
plates will do for now. For now, our examples will have an empty
Parameter_List
.
If a method returns a value, then it can return different values in different situa-
tions, but all values returned must be of the same type, which is specified as the type
returned. For example, if a method has the heading
public double
myMethod()
