Two Types of Use

Look at the example program again. When the statement

System.out.println( str );

is executed, the object referred to by str is found and its data is written to the monitor. When the statement

System.out.println( value );

is executed, the primitive value in the variable value is used directly. (It is translated into character form and written to the monitor.)

There are two kinds of variables. When used in an expression (as above) they each behave in a different way:

	Characteristics	When used in an expression:
primitive variable	Fixed number of bits. Contains the actual data.	Use the data in the variable.
reference variable	Contains information on how to find the object.	Use the reference in the variable to find the object.

When you declare a variable, you say what type it is. For example:

String str;

says that str is a reference variable expected to (later on) contain a reference to an object of type String. The declaration

long value;

says that value is a variable containing the primitive data type long. When you compile a program, the declarations tell the compiler what style of information is kept in each variable, so the compiler uses each variable in the appropriate way every time it is mentioned in your program.

str = value ;