04-TCP2103-JAVA BASIC

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JAVA Basics

TCP2103 : INTRODUCTION TO PROGRAMMING

Nurkhairizan07


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Content

PART I

Comments

Reserved words

Modifiers Statements

Blocks

Classes Methods

The main method


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Content

PART II

Data Basics

Variable & Constant


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Comments

These are the used of comments

documents what the program is and

how the program is constructed.helps programmers and users to

communicate and understand the

program.


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Comments

There are three types of comments

line comment

paragraph comment

javadoc comments


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Comments : line comment

preceded by two slash (//) on a

line.

compiler ignores all text after // on

the same line.

Example :

weight *= 2.2046; //Convert to kilograms


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Comments : block comment

enclosed between /* and */ onone or several lines.

when the compiler sees /*, it

scans for the next */ and ignoresany text between /* and */.

Example

/* Exercise 5-2 for Java MethodsAuthor: NurkhairizanDate: 21/11/2007Rev. 1.0 */


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Comments : Javadoc comment

begins with /** and end with */.

Are used for documenting

classes, data and method.

They can be extracted into a

HTML file using JDKs javadoc

command.


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JavadocComments (contd)

/*** Returns total sales from all vendors;* sets totalSales* to 0.*

* @return total amount of sales from all vendors

*/

/** indicates ajavadoccomment

Can useHTML tags

Commonstyle


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Reserved Word (Keyword)

Have a specific meaning to the compiler andcannot be used for other purpose in theprogram

Reserved words use only lowercase letters.

Reserved words include:

primitive data types: int, double, char,boolean, etc.

storage modifiers: public, private,static, final, etc.

control statements: if, else, switch,while, for, etc.

built-in constants: true, false, null

There are about 50 reserved words total.


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Modifier

Reserved words called modifiers specifythe properties of the data, methods andclasses and how they can be used.

Example of modifier are public,static private, final,abstract andprotected

Apublic modifiers for method andclass can be access by other classes.

A private datum or method cannot be

accessed by other classes.


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Statements

A statement represents an action or asequence of actions

Example

System.out.println(Welcome to Java!);

is a statement to display the greetingWelcome to Java!.

Every statement in Java ends with asemicolon (;)


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Blocks

Ablockis a group of zero or morestatements between balancedbraces ( { } )

The braces form a block thatgroups the component of theprogram

each block begins with an openingbrace({ ) and ends with a closingbrace ( })


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The useof Blocks


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Classes

The program is defined by usingone or more classes.;

Only one public class can beused in a program file.

The file name must be same as

class name (public class)


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Sample JAVA Application Program

File name Class name

Only ONE publicclass is allowedin a file!!

File name = class name

Main Method

Welcome

Class

statement


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Method

Consider the following statement

System.out.println(Hello);

System.out is known as the standard

output object.

println is a method in the object, which

consists of a collection of statement thatperform a sequence of operations to display amessage to the standard output devices.

The method can be used even without fullyunderstanding the details of how it works.


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Themain method

Every Java application must have amainmethod that defines where the program begins.

The main method provides the control ofprogram flow.

The Java interpreter executes the applicationby invoking the main method.

main method must be placed in class block


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Identifier

Programming languages use

special symbols called identifiersto name such programmingentities as variables, constants,variables, constants,

methods, classes and packagemethods, classes and package.


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Identifier

The rules for naming identifiers: An identifiers is a sequence of characters that

consists of letters, digits, underscores (_), anddollar signs ($).

An identifier must start with a letter, anunderscore(_), or dollar sign($). It cannot startwith a digit.

An identifier cannot be a reserved word.

An identifier cannot be true, false or null.

An identifier can be of any length. It cannotcontain space


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Identifier

Example for valid identifiers

myName

number1

num1

No34

Ctr

fahrenheitToCelcius

celciusToFahrenheit

_myClassNumber

$noOfStudentInClass

totalPrice


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Identifier

Example for invalid identifiers My Name : contain space

Number 1 :contain space

Num%123 : contain special symbol %

static : reserved word My-Name : contain special symbol -

Fahrenheit To Celcius contain space

Celcius-To-Fahrenheit contain specialsymbol -

45number start with digit public contain special symbol

int contain special symbol


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Java Programming Data Types

Definition : A setof values togetherwith a set

ofoperations on those values

Primitive Data Types

Integral

Floating-point

Boolean


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Data Types


integral

char

byte

short

int

long

Data types thatdeals with

integer,ornumberwithout adecimal part

Floating-

point

Boolea

n

Assign short,int orlong data types when you aresure a variableis a whole number(NO decimal

points). Whichtypeyou choosedepends upon the size

ofthe numbers.


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Data Types


Integra

l Floating-

point

Boolea

n

float

double

Data types thatdeals withdecimal numbers

Assign float ordouble when decimals are needed. Which

typeyou choosedepends upon the sizeofthe numbers


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Data Types


Integra

l Floating-

point

Boolea

n

true

false

Data types thatdeals with

logical value

Assign charifthe variablewill always contain only

ONE characterofdata


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Primitive

TypeSize Minimum Value Maximum Value Wrapper Type

char 16-bit Unicode 0 Unicode 216-1 Character

byte 8-bit -128 +127 Byte

short 16-bit-215

(-32,768)

+215-1

(32,767)Short

int 32-bit-231

(-2,147,483,648)

+231-1

(2,147,483,647)Integer

long 64-bit

-263

(-

9,223,372,036,85

4,775,808)

+263-1

(9,223,372,036,854

,775,807)

Long

float 32-bit 32-bit IEEE 754 floating-pointnumbers

Float

double 64-bit64-bit IEEE 754 floating-point

numbersDouble

boolean 1-bit true orfalse Boolean


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Review Question

Are the following identifiers valid? If no, statethe reason

applet, Applet, a++, --a, 4#R, $4,

#44, apps

Which of the following are Java keywords?

class, public, int, x, y, radius


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Variables & Constant Variable

Avariableis a named memory location whichtemporarily stores data that can change while theprogram is running.

Constant Variable : is a named memorylocation which temporarily stores data thatremains the same throughout the execution of theprogram.

Variable & Constant variable only canbe used after it has been declare.


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Variable

The syntax :

dataType identifier1;

dataType identifier1 = 3;

dataType identifier1, identifier2,

identifierN;

Example :

double amount;

int counter = 3;

char ch1, ch2, ch3;

int num1, num2;


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Variables

A variable must be declared before it can beused:

int count;double x, y;

JButton go;

Walker amy;

String firstName;

Type

Name(s)


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Variables

The assignment operator = sets thevariables value:

count = 5;x = 0;myName = (Nurkhairizan);firstName = args[0];


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Variables (contd)

A variable can be initialized in itsdeclaration:

int count = 5;

String firstName = Ahmad;


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When you declare a variable, Java reservesmemory locations of sufficient size to store thevariable type.

The actual data values will be stored in these

memory locations.


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Variable declaration

Where to declare the variables

Inside theclass, but

outside themethods

Inside the

method


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Variables (contd)

Common mistakes:

public void someMethod (...)

{int x = 0;...int x = 5; // should be: x = 5;

...Variable declared twicewithin the same scope syntax error


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Constant Variable

The syntax :

final dataType identifier = value;

Example :

final double CM_PER_INCH = 2.54;

final intNO_OF_STUDENT = 40;final double PAY_RATE = 15.57;

Keyword finalindicatetheconstant

variable


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Constant Variable

Using final you can define variableswhose values never change.

You MUST place an initial value

into such a "constant" variable.

If you do not place this initial value,Java will never let you assign a

value at a later time because youcannot do anything to change thevalue of a final (constant) variable.


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Constant Variable declaration

Where to declare constant variables

Itcan beinsidethe

class orinsidethe

method


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Printing Variables

Remember: The basic output statementin Java is

System.out.println ( );

System.out.

println(" text " );will print what is between the double

quotes and move the printing cursorto the nextline.

System.out.print ( text );will print what is between the doublequotes and leave the printing cursor onthe same line


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Printing Variables

When dealingwith variables:

System.out.println( The total pay is + totalPay);

what is surrounded by " " is referred to as a "literalprint" and gets printed exactly. The "+" sign is theconcatenator operator and concatenates the string

with the value that is stored in the variabletotalPay. totalPay is declared as a double, but isautomatically converted to a String for the purposeof printing out.

C O C O O OG G


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Printing Variable

The code :

double totalPay = 1006.5;System.out.println("The total payis " + totalPay);

On the screen:

Thetotal payis 1006.5

TCP2103 INTRODUCTION TO PROGRAMMING


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Review Question

1. The nameof a variableis known as its:

[a] identifier

[b] constant

[c] data type

[d] base

2. All variables must bedeclared beforethey

can be used. [a] true [b] false3. Variable names may begin with a

number. [a] true [b] false



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Review Question

4. When a data type mustcontain decimal

numbers, assign thetype

[a] int [b] char [c] double [d] long int

5. Variables that aredeclared, but notinitialized,contain

[a] blank spaces

[b] zeros

[c] "garbage" values

[d] nothing - they are empty



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Review Question

6. A variableis given a valuethrough

[a] a comparison statement

[b] as assignment statement

[c] the import statements

[d] the public class declarations



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Review Question

7. Declare an int variable

count withinitial value 100,anddeclare an int constantSIZE with value 20



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Using Variable in Program

Write a program to read the followinginformation:

Name

Age

IC Number Semester

Pointer

After that display all the information by using asuitable labels.



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1st Step : identify variables used

There are 5 input declare/create 5 single variablewith appropriate data type.

Name string

Age integer

ICNumberstring

Semester integer

Pointer float

String name;

int age;

String ICNo;

int Semester;

float pointer;

Capitalletter

Lowercaseletter

Identifier



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2nd Step : Write Program

1st style

2nd style

Declareeach variablein a

singleline

Group variable basedon

data type

Dont forget semicolon(;) foreach statement



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3rd Step : Prompt & accept

Use output statement to prompt user for information :

System.out.print(the prompt goes here :);

System.out.println(the prompt goes here :);

semicolon(;) indicates endof statement

Input (from keyboard) appears here



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4th Step : acceptthe information

Syntax to accept from various type of input (the inputstatement)

name = io.readLine();

age = Integer.parseInt(io.readLine());

price = Double.parseDouble(io.readLine());

point = Float.parseFloat(io.readLine());

bolF= Boolean.parseBoolean(io.readLine());

chGrade = (char)io.read();

string

integer

double

float

boolean

char



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4th Step : acceptthe information(cont)

Before you can use the input statement, followthese steps

1

2

3


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Displaythe information

\n : new line

\t : tab



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Theoutput



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The End


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04-TCP2103-JAVA BASIC