Object-Oriented Introduction to Java - Multimedia Introduction to Programming Using Java - page 25

3>=4||4>=3 true && false || true
-3<3||3>-3 true && ( false || true )
SR7. Reread Sec. 1.1.7 on function calls. Remember that, in a function call like
Math.abs(25 * -4) , the expression 25 * -4 is called the argument of the func-
tion call. Have Java evaluate some calls to the functions in class Math .
Experiment with expressions that have two or more calls, for example
Math.min(25, 4) + Math.max(25, 4) .

1.2 Variables, declarations, assignments

In mathematics, a variable is a name together with an associated value. In pro-
gramming, we use the same notion of a variable, and we draw a variable as a
named box with the value in the box. Below is an int variable called quantity
whose value is 4 .

Activity
1-4.1

4

quantity

In Java, a variable may be associated with different values at different times, but
the values must all be of the same type. For example, quantity may be associ-
ated only with values of type int . When it is important to note what the type of
a variable is, we place the type to the right of the box. Below is the same vari-
able, quantity , and a second variable price , which is of type double .

4 price 3.99

quantity

double

int

In Java, a variable must be declared before it can be used. Below are Java
declarations for variables quantity and price . Note that each declaration con-
sists of three things: a type, the name of the variable, and a semicolon.

int quantity;
double price;

In any particular context, a variable can be declared only once. For example,

Variable names, identifiers, and keywords. A variable name, like quantity , is an identifier . In
Java, identifiers are writen as a sequence of letters, digits, $ , and _, but the first
is not a digit. Java programmers do not use $ and tend not to use _ except in one
situation, which you will see later. Java programmers follow certain conventions
for identifiers, which we will explain from time to time. They are summarized
in Sec. 13.1.1.
Identifiers are case sensitive: truth and Truth are different.
Keywords (e.g. int and double ) may not be used as identifiers. To see the
list of keywords, look up keyword in the glossary of the ProgramLive CD. In
most IDEs, keywords are shown in their own distinct color, so you should not
have trouble distinguishing keywords from identifiers.