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Statements and
expressions - java
ABCs of Programming
A java program is made up of classes and objects, which are made up of
methods and variables.
Methods are made up of statements and expressions – the smallest elements
of java programming.
Looking at the basics of Java code
Statement – simple command that causes something to happen
int weight – 225;
System.out.println (“Lincoln High School is cool!”);
song.duration = 230;
Statement that produces a value is an expression
The value produced is the return value
Statements are terminated with a semicolon ;
Statements - continued
In theory, more than one statement can be put on a line, best not to.
Statements are grouped using an opening brace { and a closing brace }
A group of statements between the characters is a block.
Variables and Data Types
Java has three kinds of variables
Instance variables – define an object’s attributes
Class Variables – define the attributes of an entire class of objects
Local Variables – only used inside a method
We will work with local variables first.
In java, you must create a variable by giving it a name and declaring its type.
The type is listed first, followed by the name. EXAMPLES:
int loanLength;
String message;
boolean gameOver;
Variables and data types
EXAMPLES:
int loanLength;
String message;
boolean gameOver;
int represents integers
String is an object that holds text
boolean is used for Boolean true/false values
Local variables can be declared at any place inside a method, BUT, they must
be declared before they can be used.
You can create several variables of the same type on the same line.
String city, street, state;
Variables - continued
Variables can be assigned a value when created by using an equal = sign
followed by the value.
You must give values to local variables before you use them in a program, or
the program won’t compile successfully.
NAMING VARIABLES –
Names must start with a letter, an underscore character _ or a dollar sign $
Variables CANNOT start with a number.
camelCase naming convention is best.
Comments
Comments are essential to good programming.
Comments help to organize and provide information for you and those
working with you
I require that all programs be properly commented – get used to it!!
Single line comment two slashes // Everything from // to end of line is a
comment
Multi-line comments begins with /* and ends with */. Everything between
them is a comment
