Basic Java Chapter 2

8/14/2019 Basic Java Chapter 2

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Add Comments to a Java Program

To all programs, comments must always be present, be it short or long. It is veryessential to include comments that are non-executable statements for

documentation purposes. It helps large programs to be read easily and to

determine why the function or attributes etc. are needed in the program. It is also

reliable for future references.

Three comments in Java // ←end-of-line or single comment /* */ ← multiple line comment /** */ ← javadoc comment



Save, Compile and Execute a Java Programming

After creating a Java programming, the Java source code has to be saved with

an extention .java e.g. HelloWorld.java.

It is important that the filename and the classname must be the same.

All compilers impose case sensitive in Java.

2 steps to perform before viewing the program output:

The source code written must be compiled into bytecode

The java interpreter will then translate the bytecode into executable

statements.

How to compile a Java application

To compile HelloWorld.javado: javac HelloWorld.java

To run the application

do: java HelloWorld



Modify a Java Program

To edit the source code you may open up your existing Java source code using

any text editor.

Before the new source can be executed, the following must be performed:

1. The file with changes must be saved using the same filename

2. The program must be recompiled again with the javac command

3. The bytecode must then be interpreted by the Java interpreter, using the java

command, to execute the program



Java Programming Conventions

Three comments in java

// ←end-of-line or single comment

/* */ ← multiple line comment

/** */ ← javadoc comment

A statement is always terminated by a semicolon (;)

A block is a collection of statements bounded by opening and closing braces, it can

also be used in a class definition.

A block can also be nested

Any amount of whitespace is allowed in a Java program

Classes - names should be nouns, in mixed case, with the first letters of each word

capitalized.

Interfaces – names should be capitalized

Methods – names should be verbs, in mixed case, with the first letter in lowercase

Variables – should be in mixed case with a lowercase first letter

Constants – should be all uppercase in mixed case with a lowercase first letter

Control structures – use braces { }



Identifiers and Keywords

Identifiers are names given to a variable, class or method

You can use letters, digits, dollar signs, but the first letter of the Identifier must

always start using a letter, underscore (_) or a dollar sign.

Java identifiers are case sensitive it treats upper and lower case different

characters.

You cannot use a space or other symbols in an identifier.

Java identifiers doesn’t have maximum length.Keywords must not be used as names of a variable, class or method.

There are 48 reserved keywords:

abstract do implements private throw char finally

boolean double import protected throws native super

break else instanceof public transient volatile class

byte extends int return true float new

case false interface short try switch while

catch final long static void continue for





Data Types

There are 2 categories of data types in Java programming, which are primitive and

reference types.

Eight Primitive types of data:

boolean long byte short

char double float int

Java programming language provides for two complex data types under the

reference type.

array

class



Integer

There are four variations of data types classified under the category of integer:

byte short int long

*when defining a variable as long , a letter ‘L’ or ‘l’ must be attached behind the

value.

Type Minimum range Maximum range Size

Byte -128 127 8 bits

Short -32,768 32,767 16 bits

Int -2,147,483,648 2,147,483,647 32 bits

*long -

9,223,372,036,854,775,808

9,223,372,036,854,775,80764 bits



Floating point

A floating point number contains decimal positions. The Java programming

language supports two floating point data types: float and double.

*when defining a variable explicitly as float, a letter ‘F’ or ‘f’ must be attached

behind the value.

Type Minimum range Maximum range Size

*float -1.7e-308 1.7e+308 32 bits

double 3.4e-038 3.4e+038 64 bits



Character

There is only one data type under the category of character, which is char data

type. The char data type can only hold any single character. The value assigned

to a char must be enclosed within single quotation marks: ‘ ‘

Example: char num = ‘8’;

Array

An array is a list of variables, which all have the same data types and same

name. An array can be declared by inserting a pair of square brackets after thetype.

syntax: type array_name[]; or type[] array_name;

Class

String is a class in java programming. Each created string is a class object. A

String variable name is actually refers to a location in memory rather than to a

particular value.

Examples: String myWord = “Java is not easy”;



Separators

Separators are used to define the shape and function of Java code.

Separator Function{ } To separate blocks of code

; To delimit the end of a line code

, To separate a list of variables or values

[ ] To define and reference arrays

( ) To indicate precedence in an expression e.g. (x*y) +z

. To separate a class from a subclass e.g. System.out



Types of Operators

arithmetic operator

relational or comparison operator

logical operator

assignment operator

increment/decrement operator



Arithmetic Operator

There are five standard arithmetic operators, which can be used to manipulate

values in the programs. These operators are used in mathematical expression.

Operator Desciption

+ Addition- Subtraction

* Multiplication

/ Division

% Modulus



Operator Desciption

< Less than

> Greater than

== Equal to

<= Less than or equal to

>= Greater than or equal to

!= Not equal to

Relational or Comparison Operator

There are six comparison operators used in Java programming. A comparison

operator allows us to compare two items.



Logical Operator

There are three logical operators used in java programming. It is used in some

cases to combine compound conditions.

Operator Description

|| OR

&& AND

! NOT





Escape Sequences

In Java Programming language, we use an escape to store any characters that

includes non-printing characters such as a backspace or a tab that is in a char

variable.

Escape Sequence Description

\b Backspace

\t Tab

\n Newline or linefeed

\f Form feed

\r Carriage return

\” Double quotation mark

\’ Single quotation mark

\\ Backslash



Programming Exercises

1. State the different types of comments used in Java programming and how it

should be used.

2. Give the syntax for the following:

a. Save a Java source code

b. Compile a Java program

c. Execute a Java program

3. Explain the difference between a constant and a variable

4. State the different types of data types used in Java programming

5. List the different types of operators used in Java programming

6. Are the following statements legal:

char c = ‘a’;

int i = c + 10;

Basic Java Chapter 2

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