This
is
x:
1
This
is
y:
18
This
is
x:
2
This
is
y:
16
This
is
x:
3
This
is
y:
14
This
is
x:
4
This
is
y:
12
This
is
x:
5
This
is
y:
10
This
is
x:
6
This
is
y:
8
This
is
x:
7
This
is
y:
6
This
is
x:
8
This
is
y:
4
This
is
x:
9
This
is
y:
2
In this case, the target of the for loop is a block of code and not just a single statement.
Thus, each time the loop iterates, the three statements inside the block will be executed.
This fact is, of course, evidenced by the output generated by the program.
As you will see later in this topic, blocks of code have additional properties and uses.
However, the main reason for their existence is to create logically inseparable units of code.
Lexical Issues
Now that you have seen several short Java programs, it is time to more formally describe
the atomic elements of Java. Java programs are a collection of whitespace, identifiers, literals,
comments, operators, separators, and keywords. The operators are described in the next
chapter. The others are described next.
Whitespace
Java is a free-form language. This means that you do not need to follow any special indentation
rules. For instance, the Example program could have been written all on one line or in any
other strange way you felt like typing it, as long as there was at least one whitespace character
between each token that was not already delineated by an operator or separator. In Java,
whitespace is a space, tab, or newline.
Identifiers
Identifiers are used for class names, method names, and variable names. An identifier may
be any descriptive sequence of uppercase and lowercase letters, numbers, or the underscore
and dollar-sign characters. They must not begin with a number, lest they be confused with a
numeric literal. Again, Java is case-sensitive, so VALUE is a different identifier than Value.
Some examples of valid identifiers are
AvgTemp
count
a4
$test
this_is_ok
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