Guidelines in Writing a Java Program Adding Comments

Guidelines in Writing a Java Program

Adding Comments ¥ Three § line comments § § e. g. //comments on a line by themselves block comments § § permissible styles of comments e. g. /*comments on one line or can be extended across as many lines as needed */ Javadoc comments § e. g. /**javadoc comments generate documentation with a program named javadoc*/

¥ The java source code has to be saved with an extension. java ¥ The filename and the classname must be the same ¥ Case sensitive

Java Programming conventions ¥ Requirements when defining a classname: A classname must begin with a letter of the alphabet, an underscore or a dollar sign. ¥ A classname can contain only letter, digits, underscore or dollar signs. ¥ A classname cannot be a Java programming language reserved keyword ¥

Java Programming conventions Classname should be nouns in mixed case. ¥ Variable names declared usually begin with a lowercase first letter and should be in mixed case ¥ Constant variables declared usually are all uppercase with the words separated by underscore. ¥ Method name(procedures) declared should be verbs in mixed case with the first letter in lower case. ¥

Java Programming conventions Whitespace used to organize your program code to make reading easier. ¥ The code between a pair of curly brackets ‘{‘ and ‘}’ within any class or method is known as a block. ¥ All statements in Java programming ends with a semicolon( ; ). ¥ A statement is a single line of code. ¥

Identifiers names that are given to a variable, class or a method ¥ case sensitive Requirements in declaring an identifier: ü can used letters, digits, dollar signs and underscores ü must begin with a letter, an underscore or a dollar sign ü no maximum length of characters ü must not use of reserved words ¥

Identifiers Valid Examples Invalid Examples e. g. student name student. Name, student_name student Name, Student-name e. g. class code class. Code, class_code #code, class e. g. fee payment $payment, pay. Fee Pay Fee, pay-fee

Keywords ¥ The basic building blocks of the language abstract do implement private throw boolean double import protected throws break else instance. Of public transient byte extends int return true case false interface short try catch final long static void char finally native super volatile class float new switch white continue for null synchronized this default if package

Constants and Variables Two types of identifiers in JAVA Programming: ¥ Constants- data or values stored that do not change during the execution of the program ¥ Variables- data or values stored that can be changed during the execution of the program

Syntax to declare a constant: static final type identifier=value; The type in the declaration refers to the data type(which will be seen later in this chapter). The identifier refers to the name of the constant being defined.

Some examples of constants are: Type Examples Short Long Int Char String 2342 26357284 L 13324 ‘a’ “Hello World” Boolean True or false

Variable declaration will include the following: ¥A data type that identifies the type of data that the variable will store ¥ An identifier that is the variable’s name ¥ An optional assigned value, if we want a variable to contain an initial value ¥ A semicolon to end the declaration

Syntax to declare a variable: type identifier; The type refers to the data type, and identifier is the name of the variable being defined. type identifier 1, identifier 2; To define more than one variable with the same data type, the names will be separated by a comma.

Syntax to declare a variable: ¥ We can assign a value to a variable at the time of declaration or at any point later on after the variable is being declared. syntax: type identifier=value; or type identifier; identifier=value;

Data Types ¥ Primitive ¥ ¥ ¥ ¥ ¥ boolean byte char double float int long short Reference ¥ ¥ array class

Categories(continuation) ¥ Logical ¥ Boolean – can hold only true or false ¥ e. g. boolean answer=true; Minimum Range ¥Type Integer Maximum Range Size Byte -128 127 8 bits Short -32, 768 32, 767 16 bits Int -2, 147, 483, 648 32 bits Long 9, 223, 372. 036, 854, 775, 80 8 9, 223, 372. 036, 854, 775, 808 64 bits

Categories(continuation) ¥ Floating Point Type Minimum Range Maximum Range Size Float -1. 7 e-308 1. 7 e+308 32 bits Double 3. 4 e-038 3. 4+038 64 bits ¥ Character ¥ char ¥ e. g. char num = ‘ 8’;

Categories(continuation) ¥ Array A list of variables which all have the same data types and same name Syntax: type array_name[]; or type [] array_name; ¥

Categories(continuation) ¥ Class ¥ String ¥ Variable name refers to the location in memory rather than to a particular value. ¥ e. g. String my. Word=“Java is my favorite subject”;

Separators ¥ Used to define the shape and function of Java code Separator Function {} To separate blocks of code ; To delimit the end of a line of code , To separate a list of values or variables [] To define and reference arrays () To indicate precedence in an expression . To separate a class from a subclass

Operators ¥ Symbols used with data or variables to create mathematical or logical expressions ¥ Types: Arithmetic operator ¥ Relational or comparison operator ¥ Logical operator ¥ Assignment operator ¥ Increment/decrement operator ¥

Types of Operators ¥ Arithmetic operator Operator Description + Addition - Subtraction * Multiplication / Division % Modulus

Types of Operators ¥ Relational ¥ or comparison operator Allows us to compare two items Operator Description < Less than > Greater than == equal to <= less than or equal >= greater than or equal != not equal to

Types of Operators ¥ Logical ¥ operator Used to combine compound conditions Operator Description || OR && AND ! NOT

Types of Operators ¥ Assignment ¥ operator Represented by the equals sign (=) Initialization- assignment made when we declare a variable ¥ Assignment-assignment made later ¥

Types of Operators ¥ Increment or decrement operator Pre-increment e. g. ++identifier; ¥ Post-increment e. g. identifier++; ¥ Pre-decrement e. g. --identifier; ¥ Post-decrement e. g. identifier--; ¥

Escape Sequences ¥ Used to store any characters that includes non-printing characters Operator Description b Backspace t Tab n New line f Form feed r Carriage return ” Double quotation mark ’ Single quotation mark \ backslach