Java programs are a collection of whitespace, identifiers, literals, comments, operators, separators, and keywords
Whitespace
Java is a free-form language. This means that we 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 .
Java is case-sensitive, so VALUE is a different identifier than Value
Example of identifiers in java
| AvgTemp | count | a4 | $test | this_is_ok |
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” |
Separators in java
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. |