Methods and Formatted Output - Learning Java Through Games - page 71

i ++;
} public static void main(String [] args)

{

i=3;
inc() ;
System.out.println(i);

}

}

Unlike the two previous examples where there were two variables i (one in the main
method and one in the inc method), now we have a single variable i . No information is
passed between the methods. The main method tells the inc method to update the global
variable i .The inc method updates it and returns control to the main method. At this
point, the main method prints the value of the global variable i . For now, we will declare
all global variables as static , where the meaning of the static keyword will be discussed
in Chapter 6. Note that even global variables have scope. The scope of the variable i is
the block in which it is defined. Therefore, its scope will be the Example class. Remember
that the innermost block in which a variable is defined determines its scope. The innermost
block for the variable i is the Example class.
Comparing the two solutions, the first one is preferable. Good programming practices
call for global variables to be used sparingly. The reason is that if a global variable has an
incorrect value, then it is dicult to isolate the error. If your class contains ten methods,
then any of these methods could have changed the value of the global variable.
Note that a method can return only a single piece of information. For example, a method
that returns two integers cannot be created. Global variables are one way to solve this
problem. The method can simply modify two global variables and have void return type.
An example is shown next.

import java . util . ∗ ;
public class Example {
static int firstNumber , secondNumber ;
public static void main(String [] args) {
readTwoIntegers () ;
System. out . println(firstNumber) ;
System . out . println (secondNumber) ;

}

public static void readTwoIntegers () {

Scanner keyboard = new Scanner(System. in) ;
firstNumber = keyboard. nextInt () ;
secondNumber = keyboard . nextInt () ;

}

}

This is a bad design. Global variables should not be declared just because the
readTwoIntegers method needs to return two integers. A much better approach is to
avoid using methods that return two integers. A program with an improved design is shown
next.

import java . util . ∗ ;
public class Example {
public static void main(String [] args) {
int firstNumber , secondNumber ;
firstNumber = readInteger () ;
secondNumber = readInteger () ;