Java Reference
In-Depth Information
There has to be something missing from the definition of the
Sphere
class - there is no way to set the
value of
radius
and the other instance variables once a particular
Sphere
object is created. There is
nothing to update the value of
count
either. Adding these things to the class definition involves using
methods, so we now need to look at how a method is put together.
Defining Methods
We have been producing versions of the method
main()
since Chapter 1, so you already have an idea
of how a method is constructed. Nonetheless, we will go through from the beginning to make sure
everything is clear.
We'll start with the fundamental concepts. A method is a self-contained block of code that has a name,
and has the property that it is reusable - the same method can be executed from as many different
points in a program as you require. Methods also serve to break up large and complex calculations that
might involve many lines of code into more manageable chunks. A method is executed by calling its
name, as we will see, and the method may or may not return a value. Methods that do not return a
value are called in a statement that just does the call. Methods that do return a value are usually called
from within an expression, and the value that is returned by such a method is used in the evaluation of
the expression.
The basic structure of a method is shown below.
The specification of the
parameters for the method,
separated by commas. If the
method has no parameters,
you leave the parentheses
empty.
The type of the value to be
returned which can be any
type or class. If you specify
this as , the method
does not return a value.
void
Name of the
method.
return_type methodName arg1 arg2 argn
( , , ..., ){
This is
called the
of
//
Executable code goes here
body
the
method
}
When you specify the return type for a method, you are defining the type for the value that will be
returned by the method when you execute it. The method must always return a value of this type. To
define a method that does not return a value, you specify the return type as
void
. Something called an
access attribute
can optionally precede the return type in a method definition, but we will defer looking
into this until later in this chapter.
The parameters to a method appear in its definition between parentheses following the method name.
These specify what information is to be passed to the method when you execute it. Your methods do
not have to have parameters specified. A method that does not require any information to be passed to
it when it is executed has an empty pair of parentheses after the name.
