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 returning 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
similar 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
templates will do right 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 situations,
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()
