Introduction to JAVA PROGRAMMING STEPS ANALISA MASALAHNYA ANALISA MASALAHNYA INPUT-NYA APA SAJA?...

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Introduction to Introduction to JAVA JAVA

Transcript of Introduction to JAVA PROGRAMMING STEPS ANALISA MASALAHNYA ANALISA MASALAHNYA INPUT-NYA APA SAJA?...

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Introduction to JAVAIntroduction to JAVA

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PROGRAMMING STEPSPROGRAMMING STEPS

ANALISA MASALAHNYAANALISA MASALAHNYA INPUT-NYA APA SAJA?INPUT-NYA APA SAJA? ALGORITMA PROSESNYA BAGAIMANA?ALGORITMA PROSESNYA BAGAIMANA? OUTPUT-NYA APA?OUTPUT-NYA APA?

KETIK SOURCE CODE-NYAKETIK SOURCE CODE-NYA HEADER FILES HEADER FILES import < library >import < library > GLOBAL SECTIONS GLOBAL SECTIONS VARIABEL GLOBAL, FUNGSI BANTU VARIABEL GLOBAL, FUNGSI BANTU MAIN SECTIONS MAIN SECTIONS VARIABEL LOKAL, INPUT, PROSES, VARIABEL LOKAL, INPUT, PROSES,

OUTPUTOUTPUT COMPILE & RUN PROGRAMNYA COMPILE & RUN PROGRAMNYA ADA ADA

ERROR ?ERROR ? TES HASILNYA TES HASILNYA SUDAH BENAR ? SUDAH BENAR ? BUAT ARSIP/ DOKUMENTASINYABUAT ARSIP/ DOKUMENTASINYA

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Computers and ProgrammingComputers and Programming

A computer is a machine that can process A computer is a machine that can process data by carrying out complex calculations data by carrying out complex calculations quickly.quickly.

A A programprogram is a set of instructions for the is a set of instructions for the computer to execute.computer to execute.

A program can be A program can be high-levelhigh-level (easy for (easy for humans to understand) or humans to understand) or low-levellow-level (easy (easy for the computer to understand).for the computer to understand).

In any case, programs have to be written In any case, programs have to be written following a strict language syntax.following a strict language syntax.

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Running a ProgramRunning a Program

Typically, a program source code has to be Typically, a program source code has to be compiledcompiled into machine language before it into machine language before it can be understood by a computer.can be understood by a computer.

programmer

void test(){ println(“Hi”);}

source code (high level)

compiler

machine language

object code (low level)

writes

executed by

computer

Hi

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PortabilityPortability

Different makes of computersDifferent makes of computers speak different “languages” (machine speak different “languages” (machine

language)language) use different compilers. use different compilers.

This means that object code produced by This means that object code produced by one compiler may not work on another one compiler may not work on another computer of a different make.computer of a different make.

Thus the program is not Thus the program is not portableportable.. Java is Java is portableportable because it works in a because it works in a

different way.different way.

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History of JavaHistory of Java

The Java programming language was The Java programming language was developed at Sun Microsystemsdeveloped at Sun Microsystems

It is meant to be a It is meant to be a portableportable language language that allows the same program code that allows the same program code to be run on different computer to be run on different computer makes.makes.

Java program code is translated into Java program code is translated into byte-codebyte-code that is interpreted into that is interpreted into machine language that the computer machine language that the computer can understand.can understand.

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Java Byte-CodeJava Byte-Code

Java source code is compiled by the Java Java source code is compiled by the Java compiler into compiler into byte-codebyte-code..

Byte-code is the machine language for a Byte-code is the machine language for a ‘typical’ computer.‘typical’ computer.

This ‘typical’ computer is known as the This ‘typical’ computer is known as the Java Java Virtual MachineVirtual Machine..

A byte-code A byte-code interpreter interpreter will translate byte-will translate byte-code into object code for the particular code into object code for the particular machine.machine.

The byte-code is thus The byte-code is thus portableportable because an because an interpreter is simpler to write than a compiler.interpreter is simpler to write than a compiler.

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Running a Java ProgramRunning a Java Program

programmer

public void test() { System.out.println(“Hi”);} Java source code (high level)

Javacompiler

Machine language

object code (low level)

writes

executed by

computer

HiByte-codeinterpreter

Java byte-code

Extra step thatallows forportability

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Types of Java ProgramsTypes of Java Programs

Console Applications:Console Applications:Simple text input / outputSimple text input / outputThis is what we will be doing for most of This is what we will be doing for most of

this course as we are learning how to this course as we are learning how to program.program.public class ConsoleApp

{public static void main(String[] args){

System.out.println("Hello World!");}

}

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Types of Java ProgramsTypes of Java Programs

GUI Applications:GUI Applications:Using the Java Swing libraryUsing the Java Swing library

import javax.swing.*; public class GuiApp{

public static void main(String[] args){

JOptionPane.showMessageDialog(null, "Hello World!","GUI Application", JOptionPane.INFORMATION_MESSAGE);

System.exit(0);}

}

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Types of Java ProgramsTypes of Java Programs

Applets Applets To be viewed using a internet browserTo be viewed using a internet browser

import java.applet.*;import java.awt.*; public class AppletEg extends Applet{

public void paint(Graphics g){

g.drawString("Hello World!", 20, 20);}

}___________________________________________________<applet code="AppletEg.class" width=200 height=40></applet>

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Sample Java ProgramSample Java Programpublic classpublic class CalcCircle CalcCircle{{ public static void main(String[ ] args)public static void main(String[ ] args) {{

intint radius; radius; // radius - variable// radius - variablefinalfinal doubledouble PI = 3.14159; PI = 3.14159; // PI - constants// PI - constants

  radius = 10;radius = 10;doubledouble area = PI * radius * radius; area = PI * radius * radius;doubledouble circumference = 2 * PI * radius; circumference = 2 * PI * radius;

  System.out.println(”For a circle with radius ” + radius + System.out.println(”For a circle with radius ” + radius +

”,”);”,”);System.out.print(”The circumference is ” + circumference);System.out.print(”The circumference is ” + circumference);System.out.println(” and the area is ” + area);System.out.println(” and the area is ” + area);

}}}}

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Elements of a Java ProgramElements of a Java Program

A Java Program is made up of:A Java Program is made up of:Identifiers:Identifiers:

variablesvariablesconstantsconstants

Literal valuesLiteral valuesData typesData typesOperatorsOperatorsExpressionsExpressions

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IdentifiersIdentifiers

The identifiers in the previous The identifiers in the previous program consist of:program consist of:

public class CalcCircle{ public static void main(String[] args) {

int radius; // radius - variablefinal double PI = 3.14159; // PI - constants

 …

}}

identifier indicating name of the program(class name)

identifier to store the value of radius(variable)

identifier to store the fixed value of PI(constant)

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Data TypesData Types

Data types indicate the type of Data types indicate the type of storage required.storage required.

public class CalcCircle{ public static void main(String[ ] args) {

int radius; // radius - variablefinal double PI = 3.14159; // PI - constants

 …

}}

radius is an integer (int) value

PI is a floating-point (double) value

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Literal valuesLiteral values

Literals are the actual values stored Literals are the actual values stored in variables or used in calculations.in variables or used in calculations.

public class CalcCircle{ public static void main(String[ ] args) {

…radius = 10;…

}}

the variable radius stores the value 10

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Operators and ExpressionsOperators and Expressions

Operators allow us to perform some Operators allow us to perform some calculations on the data by forming calculations on the data by forming expressions.expressions.

public class CalcCircle{ public static void main(String[ ] args) {

…double area = PI * radius * radius;double circumference = 2 * PI * radius;…

}}

The multiplication operator (*) is used to calculate the area

An expression is formed usingoperators and operands

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Java Program StructureJava Program Structure For the next few weeks, our Java For the next few weeks, our Java

programs will have the following programs will have the following structure:structure:

public class CalcCircle{ public static void main(String[ ] args) {

// This section consists of // program code consisting of // of Java statements //

}}

The program is a class definition – use the same name as the filename.ie. Save this file as CalcCircle.java

Your program must have a mainmethod – it will start execution from here.

Curly braces indicate where sections begin and end.You should indent your code for clarity.

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Displaying OutputDisplaying OutputFor console applications, we use For console applications, we use

the System.out object to display the System.out object to display output.output.public class CalcCircle

{ public static void main(String[ ] args) {

… System.out.println(”For a circle with radius ” + radius + ”,”);System.out.print(”The circumference is ” + circumference);System.out.println(” and the area is ” + area);

}}

The text and data within the parentheseswill be output to the screen.

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Compiling and RunningCompiling and Running

The preceding source code must be saved as The preceding source code must be saved as CalcCircle.javaCalcCircle.java

You must then use the Java Development Kit You must then use the Java Development Kit (JDK) to compile the program using the (JDK) to compile the program using the commandcommandjavac CalcCircle.javajavac CalcCircle.java

The byte-code file The byte-code file CalcCircle.classCalcCircle.class will be will be created by the compiler if there are no errors.created by the compiler if there are no errors.

To run the program, use the commandTo run the program, use the commandjava CalcCirclejava CalcCircle

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Compiling and RunnngCompiling and Runnng

Buttons to compile andrun the program

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Anatomy of a Java ClassAnatomy of a Java Class

A Java console application must consist of A Java console application must consist of one class that has the following structure: one class that has the following structure:

/* This is a sample program only. Written by: Date: */public class SampleProgram{

public static void main(String [] args){

int num1 = 5; // num stores 5System.out.print("num1 has value ");

System.out.println(num1);}

}

class header

mainmethod

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Anatomy of a Java ClassAnatomy of a Java Class

A Java console application must consist of A Java console application must consist of one class that has the following structure: one class that has the following structure:

/* This is a sample program only. Written by: Date: */public class SampleProgram{

public static void main(String [] args){

int num1 = 5; // num stores 5System.out.print("num1 has value ");

System.out.println(num1);}

}

multi-line comments

in-linecomments

name of the class

statementsto be executed

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What is the result of execution?What is the result of execution?

public classpublic class CalcCircle CalcCircle{{ public static void main(String[ ] args)public static void main(String[ ] args) {{

intint radius; radius; // radius - variable// radius - variablefinalfinal doubledouble PI = 3.14159; PI = 3.14159; // PI - constants// PI - constants

  radius = 10;radius = 10;doubledouble area = PI * radius * radius; area = PI * radius * radius;doubledouble circumference = 2 * PI * radius; circumference = 2 * PI * radius;

  System.out.println(”For a circle with radius ” + radius + System.out.println(”For a circle with radius ” + radius +

”,”);”,”);System.out.print(”The circumference is ” + circumference);System.out.print(”The circumference is ” + circumference);System.out.println(” and the area is ” + area);System.out.println(” and the area is ” + area);

}}}}

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Displaying outputDisplaying output

There are some predefined classes in Java There are some predefined classes in Java that we can use for basic tasks such as:that we can use for basic tasks such as: reading inputreading input displaying outputdisplaying output

We use the We use the SystemSystem classclass to display output to display output to the screen for console applications.to the screen for console applications.

System.out System.out is an is an objectobject that provides that provides methods for displaying strings of characters methods for displaying strings of characters to the console screen.to the console screen. The The methodsmethods we can use are we can use are printprint and and printlnprintln..

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ExampleExample

Write a program that prints two lines: Write a program that prints two lines: I love Java ProgrammingI love Java Programming

It is fun!It is fun!

public class PrintTwoLines{ public static void main(String[] args) { System.out.println("I love Java Programming"); System.out.println("It is fun"); }}

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Print vs PrintlnPrint vs Println

What if you use What if you use System.out.print()System.out.print() instead?instead?

System.out.println() advances the System.out.println() advances the cursor to the next line after cursor to the next line after displaying the required output. displaying the required output.

If you use System.out.print(), you If you use System.out.print(), you might need to add spaces to format might need to add spaces to format your output clearly.your output clearly.

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ExamplesExamples

Code Fragment Output Displayed

System.out.println("First line");System.out.println("Second line");

First lineSecond line

System.out.print("First line");System.out.print("Second line");

First lineSecond line

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ExerciseExercise

Write a Java program that displays Write a Java program that displays your name and your studentID.your name and your studentID.

// Sandy Lim// Lecture 1// Printing name and student IDpublic class Information{

public static void main (String[] args){

// your code here}

}

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ExerciseExercise

Write a Java program that prints out Write a Java program that prints out to the screen the following tree:to the screen the following tree: ** ****** ************************

********

// Sandy Lim// Lecture 1// Printing a tree using *public class tree{

public static void main (String[] args){

// your code here}

}

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RemindersReminders

Get your computer accounts before Get your computer accounts before next week's tutorial so that you can next week's tutorial so that you can start programming ASAP.start programming ASAP.

Download JCreatorLE and J2SDK1.5.0, Download JCreatorLE and J2SDK1.5.0, you can access both through the you can access both through the JCreator (3.50LE) website: JCreator (3.50LE) website: http://www.jcreator.com/download.hthttp://www.jcreator.com/download.htmm

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Data Types, Data Types, Variables & Variables & OperatorsOperators

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Memory and DataMemory and DataOne of the most important components One of the most important components

of a computer system is the of a computer system is the memorymemory..A computer’s memory holds:A computer’s memory holds:

data that is to be processeddata that is to be processeddata that is the result of some processingdata that is the result of some processing

We can imagine that a computer’s We can imagine that a computer’s memory consists of boxes to hold data.memory consists of boxes to hold data.

However, the However, the sizessizes of the boxes would of the boxes would depend on the type of data that is held.depend on the type of data that is held.

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IdentifiersIdentifiers

We have to give We have to give namesnames to the boxes to the boxes we are using to store data.we are using to store data.

These names are called These names are called variable variable namesnames, or , or identifiersidentifiers..

The actual data is the The actual data is the literalliteral valuevalue of the identifier.of the identifier.

subject

BIT106 value of subject

identifier / variable name

The box is identified assubject and it stores the value “BIT106”

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Java Spelling RulesJava Spelling Rules

An identifier can consist of:An identifier can consist of:letters (A – Z, a – z) letters (A – Z, a – z) digits (0 to 9) digits (0 to 9) the characters _ and $the characters _ and $

The first character cannot be a digit.The first character cannot be a digit.

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Identifier RulesIdentifier Rules

A single identifier must be one word A single identifier must be one word only (no spaces) of any length.only (no spaces) of any length.

Java is Java is case-sensitivecase-sensitive. . Reserved WordsReserved Words cannot be cannot be

identifiers.identifiers.These are words which have a special These are words which have a special

meaning in Javameaning in Java

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ExamplesExamplesExamples of identifiersExamples of identifiers

num1num1 num2num2 first_namefirst_name lastNamelastNamenumberOfStudentsnumberOfStudents accountNumberaccountNumbermyProgrammyProgram MYPROGRAMMYPROGRAM

Examples of reserved wordsExamples of reserved wordspublicpublic ifif intint doubledouble

see Appendix 1 in the text book for others.see Appendix 1 in the text book for others. Illegal identifiersIllegal identifiers

3rdValue3rdValue my programmy program this&that this&that

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ExerciseExercise

Which of the following are valid identifier Which of the following are valid identifier names?names?my_granny’s_namemy_granny’s_namejoesCarjoesCarintegerinteger2ndNum2ndNumChild3Child3 doubledouble third valuethird value mid2charsmid2chars PUBLICPUBLIC

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Types of DataTypes of Data

What kind of data can be collected for use What kind of data can be collected for use in a computer system?in a computer system?

Consider data on:Consider data on: College application formCollege application form Student transcriptStudent transcript Role Playing Game (RPG)Role Playing Game (RPG)

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Types of DataTypes of Data

We typically want to collect data which We typically want to collect data which may bemay be numericnumeric characterscharacters StringsStrings choice (Y/N)choice (Y/N)

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Java Data TypesJava Data Types In order to determine the sizes of storage (boxes) In order to determine the sizes of storage (boxes)

required to hold data, we have to required to hold data, we have to declaredeclare the the data data typestypes of the identifiers used. of the identifiers used.

Integer data types are used to hold whole numbers Integer data types are used to hold whole numbers 0, -10, 99, 10010, -10, 99, 1001

The Character data type is used to hold any single The Character data type is used to hold any single character from the computer keyboardcharacter from the computer keyboard '>', 'h', '8''>', 'h', '8'

Floating-point data types can hold numbers with a Floating-point data types can hold numbers with a decimal point and a fractional part.decimal point and a fractional part. -2.3, 6.99992, 5e6, 1.5f-2.3, 6.99992, 5e6, 1.5f

The Boolean data type can hold the values The Boolean data type can hold the values truetrue or or falsefalse..

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Primitive vs Primitive vs Reference Data TypesReference Data Types

A data type can be a:A data type can be a:Primitive typePrimitive typeReference type (or Class type)Reference type (or Class type)

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Primitive vs Reference Data Primitive vs Reference Data TypesTypes

A Primitive type is one that holds a A Primitive type is one that holds a simple, indecomposable value, such simple, indecomposable value, such as:as:a single numbera single numbera single charactera single character

A Reference type is a type for a A Reference type is a type for a classclass::it can hold objects that have data and it can hold objects that have data and

methods methods

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Java Primitive Data TypesJava Primitive Data TypesThere are 8 primitive data types in JavaThere are 8 primitive data types in Java

Type nameType name Kind of valueKind of value Memory usedMemory used

bytebyte integerinteger 1 byte1 byte

shortshort integerinteger 2 bytes2 bytes

intint integerinteger 4 bytes4 bytes

longlong integerinteger 8 bytes8 bytes

floatfloat floating-point numberfloating-point number 4 bytes4 bytes

double double floating-point numberfloating-point number 8 bytes8 bytes

charchar single charactersingle character 2 bytes2 bytes

booleanboolean true or falsetrue or false 1 bit1 bit

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Declaring variablesDeclaring variables

When we want to store some data in When we want to store some data in a variable,a variable,we must first we must first declaredeclare that variable. that variable.to prepare memory storage for that to prepare memory storage for that

data.data.Syntax:Syntax:

Type VariableName;Type VariableName;

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Declaring variablesDeclaring variables

Examples:Examples:The following statements will declareThe following statements will declare

an integer variable called studentNumber to an integer variable called studentNumber to store a student number: store a student number:

a double variable to store the score for a studenta double variable to store the score for a studenta character variable to store the lettergradea character variable to store the lettergrade

public static void main(String[] args){

// declaring variablesint studentNumber;double score;char letterGrade;

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Assignment StatementsAssignment Statements Once we have declared our variables, we Once we have declared our variables, we

can use the variables to hold data.can use the variables to hold data. This is done by This is done by assigningassigning literal values literal values

to the variables.to the variables. Syntax (for primitive types):Syntax (for primitive types):

VariableName = value;VariableName = value; This means that the value on the right hand This means that the value on the right hand

side is evaluated and the variable on the left side is evaluated and the variable on the left hand side is set to this value.hand side is set to this value.

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Assignment StatementsAssignment Statements Examples:Examples:

Setting the student number, score and lettergrade Setting the student number, score and lettergrade for the variables declared earlier:for the variables declared earlier:

public static void main(String[] args){

// declaring variablesint studentNumber;double score;char letterGrade;

// assigning values to variablesstudentNumber = 100;score = 50.8;letterGrade = 'D';

}

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Initializing VariablesInitializing Variables We may also We may also initialize initialize variables when variables when

declaring them.declaring them. Syntax:Syntax:

Type VariableName = value;Type VariableName = value; This will set the value of the variable the This will set the value of the variable the

moment it is declared. moment it is declared. This is to protect against using variables This is to protect against using variables

whose values are undetermined.whose values are undetermined.

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Initializing VariablesInitializing Variables Example: the variables are initialized as Example: the variables are initialized as

they are declared:they are declared:

public static void main(String[] args){

// declaring variablesint studentNumber = 100;double score = 50.8;char letterGrade = 'D';

}

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Arithmetic OperatorsArithmetic Operators

We can use arithmetic operators in We can use arithmetic operators in our assignment statements.our assignment statements.

The Java arithmetic operators are:The Java arithmetic operators are: addition, +addition, + (integer and floating-point)(integer and floating-point) subtraction, -subtraction, - (integer and floating-(integer and floating-

point)point) multiplication, * multiplication, * (integer and floating-point)(integer and floating-point) division, / division, / (integer and floating-point) (integer and floating-point) modulus, %modulus, % (integer division to find remainder)(integer division to find remainder)

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Arithmetic OperatorsArithmetic Operators

Example: using the + operatorExample: using the + operatorpublic static void main(String[] args){

// declaring two integer variablesint num1 = 5, num2 = 8;

// declaring a variable to store the totalint total;

// performing addition:total = num1 + num2;

// display resultSystem.out.println(“total = “ + total);

}

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Arithmetic ExpressionsArithmetic ExpressionsMore examples of expressions:More examples of expressions:public static void main(String[] args){

// declaring variablesint num1 = 5, num2 = 8; int quotient, remainder;double total, average;

// performing arithmetic:total = num1 + num2;average = total / 2; // floating-point division

quotient = num1 / num2; //integer divisionremainder = num1 % num2;

// how to display the results?}

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Operator PrecedenceOperator Precedence

Operators follow Operators follow precedence rulesprecedence rules::Thus you should use parentheses ( ) Thus you should use parentheses ( )

where necessary.where necessary.Generally according to algebraic Generally according to algebraic

rules:rules:( ) , * , / , % , + , -( ) , * , / , % , + , -

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Operator PrecedenceOperator Precedence

Example:Example:The expressionsThe expressions

3 + 5 * 5 will evaluate to 283 + 5 * 5 will evaluate to 28(3 + 5) * 5 will evaluate to 40(3 + 5) * 5 will evaluate to 40

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Assignment CompatibilitiesAssignment CompatibilitiesIn an assignment statement, you In an assignment statement, you

can assign a value of one type can assign a value of one type into another type:into another type:int iVariable = 6;double dblVariable;dblVariable = iVariable; // assigning int to double

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Assignment CompatibilitiesAssignment CompatibilitiesHowever, you can not directly However, you can not directly

assign a double into an intassign a double into an intdouble dblVariable = 6.75; int iVariable;iVariable = dblVariable;

// assigning double to intCompiler error! Possible loss of precision

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Type CastingType CastingGenerally, you can only assign a Generally, you can only assign a

type to the type appearing further type to the type appearing further down the list:down the list:byte > short > int > long > float > doublebyte > short > int > long > float > double

However, if you wish to change a However, if you wish to change a doubledouble type to an type to an intint, you must use , you must use type castingtype casting

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Type Casting: ExampleType Casting: Example

The value of iVariable is now 6The value of iVariable is now 6The value of The value of dblVariabledblVariable is truncated is truncated

and assigned to and assigned to iVariableiVariable..The value of The value of dblVariabledblVariable remains remains

6.756.75

double dblVariable = 6.75; int iVariable;iVariable = (int) dblVariable;

// assigning double to int by typecasting

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Sample ProgramSample ProgramLet's have a look at the following Let's have a look at the following

program. What does it do?program. What does it do?public class SimpleMaths{

public static void main (String[] args){

int num1 = 5, num2 = 6;int sum, diff, product, quotient, remainder;

sum = num1 + num2;diff = num1 - num2;product = num1 * num2;quotient = num1 / num2;remainder = num1 % num2;

}}

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Displaying outputDisplaying output

We must use display the results We must use display the results obtainedobtained

public class SimpleMaths{

public static void main (String[] args){

int num1 = 5, num2 = 6;int sum, diff, product, quotient, remainder;sum = num1 + num2;diff = num1 - num2;… System.out.println(sum);System.out.println(diff);// etc

}}

displays the value stored in the variable sum

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Displaying outputDisplaying output However, we should always make our However, we should always make our

output meaningful and clear.output meaningful and clear.public class SimpleMaths{

public static void main (String[] args){

int num1 = 5, num2 = 6;int sum, diff, product, quotient, remainder;sum = num1 + num2;…

System.out.println("The sum is");System.out.println(sum);// etc

}}

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Displaying outputDisplaying outputWe can use the System.out.print() We can use the System.out.print()

method:method:public class SimpleMaths{

public static void main (String [] args){

int num1 = 5, num2 = 6;int sum, diff, product, quotient, remainder;sum = num1 + num2;…

System.out.print("The sum is ");System.out.println(sum);// etc

}}

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Displaying outputDisplaying output

We can combine Strings and data using We can combine Strings and data using the concatenation operator +the concatenation operator +

public class SimpleMaths{

public static void main (String [] args){

int num1 = 5, num2 = 6;int sum, diff, product, quotient, remainder;sum = num1 + num2;…

System.out.print("The sum is " + sum);

// etc}

}

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Concatenation + Concatenation +

The symbol '+' has two meanings in The symbol '+' has two meanings in JavaJavaAddition plus, which adds two numbersAddition plus, which adds two numbersConcatenation plus, which joins Strings Concatenation plus, which joins Strings

or text together.or text together.

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Concatenation + Concatenation +

'+' will be used for '+' will be used for additionaddition if: if:both operands are numericboth operands are numeric

System.out.println(8 + 6);System.out.println(17.5 + 4);

System.out.println("8" + 6);System.out.println(8 + "6”)System.out.println("8" + "6”)System.out.println("The answer is " + 14);System.out.println("The answer is " + 8 + 6);

'+' will be used to '+' will be used to concatenateconcatenate if: if:if either operand is a String or textif either operand is a String or text

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ExerciseExercise

Write a Java program that sets the Write a Java program that sets the values of three integer-valued values of three integer-valued assignment scores and then assignment scores and then calculates and displays:calculates and displays:the total of the three scoresthe total of the three scoresthe average of the three scoresthe average of the three scores

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ExerciseExercise What is wrong with the following program?What is wrong with the following program?

public class countAvg{

public static void main (String[] args){

int score1, score2;double average = 0.0;score1 = 56;score2 = 73;average = score1 + score2 / 2System.out.print("The average of ");System.out.print(score1);System.out.print("and");System.out.println(score2);System.out.println("is " + average);

}}

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The The CharChar data type data typeAnother primitive data type is Another primitive data type is charcharThe The charchar data type can hold values of data type can hold values of

the following character literals:the following character literals:the letters of the alphabet, eg.: the letters of the alphabet, eg.: 'A', 'b''A', 'b'the digits, eg. : the digits, eg. : '0' , '3''0' , '3'other special symbols, eg.: other special symbols, eg.: '(', '&', '+' '(', '&', '+' the null (empty) character: the null (empty) character: ''''

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The The CharChar data type data type Invalid character literals:Invalid character literals:

"a""a" – this is a string – this is a string'aB''aB' – these are two characters – these are two characters'''''' – three consecutive single quotes: – three consecutive single quotes:

what does it mean?what does it mean?

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Escape SequenceEscape Sequence

Sometimes it is necessary to Sometimes it is necessary to represent symbols:represent symbols:which already have special meanings in which already have special meanings in

the Java language, such as ' or "the Java language, such as ' or "other characters such as a tab or return.other characters such as a tab or return.

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Escape SequenceEscape Sequence

The escape sequence character \ is The escape sequence character \ is used in this case.used in this case.'\'' '\'' to represent the single quote to represent the single quote

charactercharacter'\"' '\"' to represent the double quote to represent the double quote

charactercharacter'\\' '\\' to represent a backslash to represent a backslash

character. character. '\t''\t' to represent a tab to represent a tab'\n''\n' to create a new line to create a new line

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ExerciseExercise

Write a program that will display Write a program that will display the following:the following:She said "Hello!" to me!She said "Hello!" to me!

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The The StringString Data Type Data Type

A A String String type is an example of a type is an example of a reference data type.reference data type.

A string is defined as a sequence of A string is defined as a sequence of characters.characters.

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The The StringString Data Type Data Type

Examples of String literals:Examples of String literals:" " (space, not the character ' ')" " (space, not the character ' ')"" (empty String)"" (empty String)"a""a""HELLO" "HELLO" "This is a String""This is a String""\tThis is also a String\n""\tThis is also a String\n"

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Declaring a StringDeclaring a String

Strings can be used to store names, Strings can be used to store names, titles, etc.titles, etc.

We can declare a String data type by We can declare a String data type by giving it a variable name:giving it a variable name: String name;String name;

We can also initialize the variable We can also initialize the variable upon declaration:upon declaration: String subjectCode = “BIT106”;String subjectCode = “BIT106”;

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ExerciseExerciseWrite a program to print out the Write a program to print out the

following, using String variables:following, using String variables:Subject code: BIT106Subject code: BIT106Subject name: Java ProgrammingSubject name: Java ProgrammingStudent name: Lee Ah YewStudent name: Lee Ah YewAssignment 1 Score (out of 25): 24.0 Assignment 1 Score (out of 25): 24.0 Assignment 2 Score (out of 25): 23.5Assignment 2 Score (out of 25): 23.5Exam Raw Score (out of 50) : 48.90Exam Raw Score (out of 50) : 48.90

Lee Ah Yew's Total Score for BIT106 (Java Lee Ah Yew's Total Score for BIT106 (Java Programming): 96.40 Programming): 96.40

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Keyboard InputKeyboard Input

Java 5.0 has reasonable facilities for Java 5.0 has reasonable facilities for handling keyboard input.handling keyboard input.

These facilities are provided by the These facilities are provided by the ScannerScanner class in the class in the java.utiljava.util package.package.A A packagepackage is a library of classes. is a library of classes.

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Using the Scanner ClassUsing the Scanner Class

Near the beginning of your program, insertNear the beginning of your program, insert

import java.util.*import java.util.* Create an object of the Create an object of the ScannerScanner class class

Scanner sc = new Scanner Scanner sc = new Scanner (System.in)(System.in)

Read data (an Read data (an intint or a or a doubledouble, for , for example)example)

int n1 = sc.nextInt();int n1 = sc.nextInt();

double d1 = sc.nextDouble();double d1 = sc.nextDouble();

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Keyboard Input DemonstrationKeyboard Input Demonstration

class ScannerDemoclass ScannerDemo

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Some Some ScannerScanner Class Methods Class Methods

syntaxsyntax

Int_Variable = Object_NameInt_Variable = Object_Name.nextInt();.nextInt();

Double_Variable = Double_Variable = Object_NameObject_Name.nextDouble();.nextDouble();

String_Variable = Object_NameString_Variable = Object_Name.next();.next();

String_Variable = Object_NameString_Variable = Object_Name.nextLine();.nextLine();

Remember to prompt the user for Remember to prompt the user for input, e.g.input, e.g.System.out.print(“Enter an integer: “);System.out.print(“Enter an integer: “);

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Interactive InputInteractive InputYou should always You should always promptprompt the user the user

when obtaining data:when obtaining data:

Please enter your name: Sandy Lim

Please enter your age: 25

Please enter your score: 87.9Please enter your grade: A

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ExerciseExercise

Write a program that asks the user to Write a program that asks the user to enter the name of an item, the price enter the name of an item, the price and the quantity purchased. The and the quantity purchased. The program must calculate the total price program must calculate the total price and display the following:and display the following:

ItemItem UnitUnit QtyQty Total Total

widget widget RM5.30RM5.30 1010 RM53.00 RM53.00

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PseudocodePseudocode When we want to write a computer When we want to write a computer

program, we should always:program, we should always: ThinkThink PlanPlan CodeCode

We can write out our planning using We can write out our planning using pseudocodepseudocode – writing out the steps in – writing out the steps in simple English and not strict programming simple English and not strict programming language syntax.language syntax.

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DocumentationDocumentation

A computer programmer generally spends A computer programmer generally spends more time more time readingreading and modifying and modifying programs than writing new ones.programs than writing new ones.

It is therefore important that your It is therefore important that your programs are documented:programs are documented: clearlyclearly neatlyneatly meaningfullymeaningfully

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DocumentationDocumentation

You should always precede your program You should always precede your program with:with: Your nameYour name The dateThe date The purpose of the programThe purpose of the program

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CommentsComments

Comments are used to:Comments are used to:Insert documentationInsert documentationClarify parts of code which may be Clarify parts of code which may be

complex.complex.Comments are ignored by the Comments are ignored by the

compiler but are useful to humans.compiler but are useful to humans.

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CommentsComments

The symbols // are used to indicate that The symbols // are used to indicate that the rest of a line are comments.the rest of a line are comments.

If comments span more than one line, the If comments span more than one line, the symbols /* and */ can be used, eg.:symbols /* and */ can be used, eg.:/* this is the beginning of the documented /* this is the beginning of the documented comments and it only ends here */comments and it only ends here */

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Variable namesVariable names

Variable names shoud:Variable names shoud:follow the Java rulesfollow the Java rulesbe be meaningfulmeaningful

For example, For example, namename, , score, totalBeforeTaxesscore, totalBeforeTaxesYou should almost never use names likeYou should almost never use names likea, b, ca, b, c

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Variable namesVariable names

By convention:By convention:variable names start with a lowercase variable names start with a lowercase

letterletterclass names start with an uppercase class names start with an uppercase

letter, eg. letter, eg. String, ScannerString, Scanner

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IndentationIndentation

Programs are also Programs are also indentedindented for for clarityclarity

Indentation shows the levels of Indentation shows the levels of nesting for the program.nesting for the program.public class CalcCircle

{public static void main(String[] args){

int radius; // radius - variablefinal double PI = 3.14159; // PI - constants

 radius = 10;double area = PI * radius * radius;double circumference = 2 * PI * radius;

}}

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ExerciseExercise

Write a program that asks the user Write a program that asks the user for their name and the year they for their name and the year they were born. Then display their age were born. Then display their age this year.this year.What is your name? KellyWhat is your year of birth? 1982Wow, Kelly, this year you will be 21 years old!

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ExerciseExercise

Write a program that asks the user to Write a program that asks the user to enter the length and width of a enter the length and width of a rectangle and then display:rectangle and then display:the area of the rectanglethe area of the rectanglethe perimeter of the rectanglethe perimeter of the rectangle

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The Math class: We can use pre-defined methods from The Math class: We can use pre-defined methods from the Math class to perform calculations.the Math class to perform calculations.

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ExerciseExercise Write a Java program that asks the user to enter Write a Java program that asks the user to enter

two numbers, then:two numbers, then: find the absolute value of each of the numbers;find the absolute value of each of the numbers; determine which absolute value is largerdetermine which absolute value is larger find the square root of the larger of the two absolute find the square root of the larger of the two absolute

valuesvaluesSample run:Sample run:Enter first number: Enter first number: -36-36Enter second number: Enter second number: 55The absolute values of the two numbers are 36 and 5The absolute values of the two numbers are 36 and 5The larger absolute value is 36The larger absolute value is 36The square root of 36 is 6.0The square root of 36 is 6.0

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Catch-up ExerciseCatch-up Exercise

Write a Java program that asks the Write a Java program that asks the user to enter a double number. Then user to enter a double number. Then display:display:the square root of the number.the square root of the number.

Now test the program with the values:Now test the program with the values:39.439.4-30-30

We want to be able to make sure that We want to be able to make sure that the user cannot enter negative values!the user cannot enter negative values!