Invalid identifier names include these:
2count
high-temp
Not/ok
Literals
A constant value in Java is created by using a literal representation of it. For example, here
are some literals:
100
98.6
'X'
"This is a test"
Left to right, the first literal specifies an integer, the next is a floating-point value, the third is
a character constant, and the last is a string. A literal can be used anywhere a value of its type
is allowed.
Comments
As mentioned, there are three types of comments defined by Java. You have already seen two:
single-line and multiline. The third type is called a documentation comment. This type of comment
is used to produce an HTML file that documents your program. The documentation comment
begins with a /** and ends with a */. Documentation comments are explained in Appendix A.
Separators
In Java, there are a few characters that are used as separators. The most commonly used
separator in Java is the semicolon. As you have seen, it is used to terminate statements.
The separators are shown in the following table:
Symbol Name
Purpose
()
Parentheses Used to contain lists of parameters in method definition and invocation.
Also used for defining precedence in expressions, containing expressions
in control statements, and surrounding cast types.
{}
Braces
Used to contain the values of automatically initialized arrays. Also used
to define a block of code, for classes, methods, and local scopes.
[]
Brackets
Used to declare array types. Also used when dereferencing array values.
;
Semicolon
Terminates statements.
,
Comma
Separates consecutive identifiers in a variable declaration. Also used to
chain statements together inside a for statement.
.
Period
Used to separate package names from subpackages and classes. Also
used to separate a variable or method from a reference variable.
The Java Keywords
There are 50 keywords currently defined in the Java language (see Table 2-1). These keywords,
combined with the syntax of the operators and separators, form the foundation of the Java
language. These keywords cannot be used as names for a variable, class, or method.
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