Language basics - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 31

Reference variables refer to an object (see Chapter 3):

Vector vec = new Vector (); // vec is a reference to a
// Vector object

Array variables (see Chapter 3):

x = b*c[5]; // c[5] refers to the element at index 5
// of array c
Literals -Aspecific value in a line of code is called a literal:

double x = 4.0; // 4.0 is the double floating-point
// literal
String str =" Astring " ;// " Astring " is a string literal
char c =' c ' ; // ' c ' is a character literal

2.2.2 Language structures
The basic language elements above combine to create higher-level structures that
perform the operations of a program. These structures include:

Expressions -Anexpression contains an operation on one or more operands and returns
avalue:
x = 5 - assignment operation
x < 5 - comparison operation
14.*y - multiplication operation
Statements -Astatement, which can hold one or more expressions, presents a complete
action or set of actions to perform:

x = 5;
if (y < 5) x = 3;
return 3.0*(14.*y);

Statements end with a semicolon.

Finally, these structures in turn make up the structure of a class and its fields
and methods (methods resemble subroutines or functions in other languages). We
fully develop the definition of Java classes in later chapters.

2.3 A simple application
The following example code illustrates the bare essentials of a Java application
program that prints a short text string to the console. You can see that the code
must always occur within the framework of a class. Follow the instructions in
Chapter 1 for compiling and executing this application.