Java Words Symbols and Rules Java Program Structure

Java • Words, Symbols and Rules

Java Program Structure • JAVA program: § A program is made up of one or more classes. The inside name of the class should always match the outside name of the class. § A class contains one or more methods You need to have a main method. Java looks for it in order to begin execution. § A method contains program statements Such as: System. out. println(“Some String”);

Program Statements • Almost every statement ends in a semicolon. There are very few exceptions. • Be careful with statement indentation § You will increase indentation after an opening bracket “{“ § You will decrease indentation after a closing bracket “}”

Elements of Programming • We need to reserve memory in order to store the different values that will be used by our program to perform calculations.

Variable Declaration and Initialization • Declaring a variable int x; • Initializing a variable x = 5; • Declaring and initializing int x = 5; 5

Variable declaration and comments • One variable declaration per line please • After the declaration/initialization you should describe what the variable does. int age, years. Of. Marriage, number. Of. Children; int age = 25; //the persons age

In Memory int x = 5; 5 X

Overwrite int x = 5; x = 3; 5 3 X

Identifiers • Identifiers/Variable names are the words a programmer uses in a program • An identifier can be made up of letters, digits, the underscore character ( _ ), and the dollar sign • Identifiers cannot begin with a digit • Java is case sensitive 9

Primitive Data types • int • double • char • boolean

Reserved Words • A reserved word cannot be used in any other way • The Java reserved words: abstract assert boolean break byte case catch char class const continue default do double else enum extends false finally float for goto if implements import instanceof interface long native new null package private protected public return short static strictfp super switch synchronized this throws transient true try void volatile while 11