Java Reference
In-Depth Information
Good Programming Practice 2.8
Choosing meaningful variable names helps a program to be self-documenting (i.e., one
can understand the program simply by reading it rather than by reading associated docu-
mentation or creating and viewing an excessive number of comments).
Good Programming Practice 2.9
By convention, variable-name identifiers begin with a lowercase letter, and every word in
the name after the first word begins with a capital letter. For example, variable-name iden-
tifier
firstNumber
starts its second word,
Number
, with a capital
N
. This naming conven-
tion is known as
camel case
, because the uppercase letters stand out like a camel's humps.
Line 17
System.out.print(
"Enter first integer: "
);
// prompt
uses
System.out.print
to display the message
"Enter first integer: "
. This message is
called a
prompt
because it directs the user to take a specific action. We use method
print
here rather than
println
so that the user's input appears on the same line as the prompt.
Recall from Section 2.2 that identifiers starting with capital letters typically represent class
names. Class
System
is part of package
java.lang
. Notice that class
System
is
not
import-
ed with an
import
declaration at the beginning of the program.
Software Engineering Observation 2.2
By default, package
java.lang
is imported in every Java program; thus, classes in
java.lang
are the only ones in the Java API that do not require an
import
declaration.
Line 18
number1 = input.nextInt();
// read first number from user
uses
Scanner
object
input
's
nextInt
method to obtain an integer from the user at the key-
board. At this point the program
waits
for the user to type the number and press the
Enter
key to submit the number to the program.
Our program assumes that the user enters a valid integer value. If not, a runtime logic
error will occur and the program will terminate. Chapter 11, Exception Handling: A
Deeper Look, discusses how to make your programs more robust by enabling them to
handle such errors. This is also known as making your program
fault tolerant
.
In line 18, we place the result of the call to method
nextInt
(an
int
value) in variable
number1
by using the
assignment operator
,
=
. The statement is read as “
number1
gets
the
value of
input.nextInt()
.” Operator
=
is called a
binary operator
, because it has
two
operands
—
number1
and the result of the method call
input.nextInt()
. This statement
is called an
assignment statement
, because it
assigns
a value to a variable. Everything to the
right
of the assignment operator,
=
, is always evaluated
before
the assignment is performed.
Good Programming Practice 2.10
Place spaces on either side of a binary operator for readability.
