Defining Methods

Here is an example of a typical method declaration:

public double calculateAnswer(double wingSpan, int numberOfEngines, double length, double grossTons) {

	//do the calculation here

}

The only required elements of a method declaration are the
method's return type, name, a pair of parentheses,
(), and a body between braces, {}.


More generally, method declarations have six components, in order:

1. Modifiers—such as public, private, and others you will learn about later.
   


2. The return type—the data type of the value returned by the method, or void if the method does not return a value.
   


3. The method name—the rules for field names apply to method names as well, but the convention is a little different.
   


4. The parameter list in parenthesis—a comma-delimited list of input parameters, preceded by their data types,
   enclosed by parentheses, (). If there are no parameters, you must use empty parentheses.
   


5. An exception list—to be discussed later.
   


6. The method body, enclosed between braces—the method's code, including the declaration of local variables, goes here.

Modifiers, return types, and parameters will be discussed later in this


lesson.

Exceptions are discussed in a later
lesson.

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Definition: Two of the components of a method declaration comprise the
method signature—the method's name and the parameter types.

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The signature of the method declared above is:

calculateAnswer(double, int, double, double)

Naming a Method

Although a method name can be any legal identifier, code conventions restrict method names. By convention, method names
should be a verb in lowercase or a multi-word name that begins with a verb in lowercase, followed by adjectives, nouns, etc.
In multi-word names, the first letter of each of the second and following words should be capitalized. Here are some examples:

run

runFast

getBackground

getFinalData

compareTo

setX

isEmpty

Typically, a method has a unique name within its class. However, a method might
have the same name as other methods due to method overloading.

Overloading Methods

The Java programming language supports overloading methods, and Java can
distinguish between methods with different method signatures. This means that methods within a class
can have the same name if they have different parameter lists (there are some qualifications to this that
will be discussed in
the lesson titled
"Interfaces and Inheritance").



Suppose that you have a class that can use calligraphy to draw various types of data
(strings, integers, and so on) and that contains a method for drawing
each data type. It is cumbersome to use a new name
for each method—for example, drawString,
drawInteger, drawFloat, and so on.
In the Java programming language, you can use the same name for
all the drawing methods but pass a different argument list to
each method. Thus, the data drawing class might declare four
methods named draw, each of which has a different
parameter list.

public class DataArtist {

	...

	public void draw(String s) {

		...

	}

	public void draw(int i) {

		...

	}

	public void draw(double f) {

		...

	}

	public void draw(int i, double f) {

		...

	}

}

Overloaded methods are differentiated by the number and
the type of the arguments passed into the method. In the
code sample, draw(String s) and draw(int i)
are distinct and unique methods because they require different
argument types.

You cannot declare more than one method with
the same name and the same number and type of arguments,
because the compiler cannot tell them apart.



The compiler
does not consider return type when differentiating methods,
so you cannot declare two methods with the same signature
even if they have a different return type.

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