Sams Teach Yourself Java™ in 24 Hours (Covering Java 7 and Android)

ptg7068951

Creating Behavior with Methods 141

You have been using methods throughout your programs up to this point
without knowing it, including one in particular: println(). This method
displays text onscreen. Like variables, methods are used in connection with
an object or a class. The name of the object or class is followed by a period
and the name of the method, as in screen2D.drawString()or
Integer.parseInt().

Declaring a Method

You create methods with a statement that looks similar to the statement
that begins a class. Both can take arguments between parentheses after
their names, and both use {and }marks at the beginning and end. The
difference is that methods can send back a value after they are handled.
The value can be one of the simple types such as integers or Boolean val-
ues, or it can be a class of objects.

The following is an example of a method the Virusclass can use to infect
files:

public booleaninfectFile(String filename) {
booleansuccess = false;
// file-infecting statements go here
return success;
}

This method takes a single argument: a string variable called filename,
which is a variable that represents the file that should be attacked. If the
infection is a success, the successvariable is set to true.

In the statement that begins the method, booleanprecedes the name of the
method, infectFile. This statement signifies that a booleanvalue is sent
back after the method is handled. The returnstatement is what actually
sends a value back. In this method, the value of successis returned.

If a method should not return a value, use the keywordvoid.

When a method returns a value, you can use the method as part of an
expression. For example, if you created a Virusobject called malaria, you
could use statements such as these:

if (malaria.infectFile(currentFile)) {
System.out.println(currentFile + “ has been infected!”);
} else{
System.out.println(“Curses! Foiled again!”);
}

NOTE

TheSystem.out.println()

method might seem confusing

because it has two periods

instead of one. This is because

two classes are involved in the

statement—theSystemclass

and the PrintStreamclass.

TheSystemclass has a variable

calledoutthat is a

PrintStreamobject.println()

is a method of the PrintStream

class. The System.out.print-

ln()statement means,in

effect,“Use the println()

method of the outvariable of

theSystemclass.” You can

chain together references in

this way.