csc1030 hands-on introduction to java

CSC1030HANDS-ON INTRODUCTION

TO JAVA Loop, Primitive type & Object basics

Three Kinds of Looping Statementswhile (condition) {

loop_body;

}

do {

loop_body;

} while (condition);

for (start; condition; update) {

loop_body;

}

Supplemented by:•break;•continue;

For example: while-loopclass Main{ public static void main (String [ ] args) { int i = 1; // declare a variable

// a while-loop while ( i < 10 ) // while "i < 10 is true" { System.out.println(i); i = i + 1; // increment i }

System.out.println(i); // what will i be?

}}

For example: do-while-loopclass Main{ public static void main (String [ ] args) { int i = 1; // declare a variable

// a do-while-loop do { // do at least once System.out.println(i); i = i + 1; // increment i } while ( i < 10 ); // while "i < 10 is true"


}}

For example: for-loopclass Main{ public static void main (String [ ] args) { int i; // declare a variable

// a for-loop (start; check; update) for ( i = 1; i < 10; i++ ) { // i runs from 1 to 9 System.out.println(i); }


}}

break and continue break: stops a loop right away.

continue: stop the current iteration AND continue the next round!

Outline The Java API Using the Math Class

Lab Exercise: Quadratic Equation Solver Java Primitive Data Types Java Class (Object) Types Using the String Objects

Lab Exercise: String Manipulation

The Java API System, String, JOptionPane, etc.

are stuffs provided in the Java Application Programming Interface (API).

System.out.println(...);

String answer;

JOptionPane.showInputDialog(...);

The Java API Reference Manualhttp://java.sun.com/javase/6/docs/api/

The Java API Reference ManualQuick Reference Using NetBeans

Importance of the Java API The API provides extra functionalities and tools, however.

As a Java programmer, we do NOT have to memorize all the stuffs provided in the API.

However, we should understand, look-up and make use of the API library properly.

Better though, we recite the spelling and usage of some commonly used ones, such as System, String, etc

Contributing to the World-Wide API As a Computer Professional, sometimes we

create something to make a contribution.

Others could then possibly make use of our work.

In such case, we have to well-design, well-test and well-document our contribution.

The Math Class Well, System is a Java Class.

String is also a Java Class.

So as JOptionPane.

We are going to make use of another useful and important Java Class, the Math Class.

Using the Math Classclass Main{ public static void main (String [ ] args) { String deg; deg = JOptionPane.showInputDialog("An angle in deg:");

// convert the angle (text input) to a number double angle_in_degree; angle_in_degree = Double.parseDouble( deg );

double angle_in_radian; angle_in_radian = Math.toRadians( angle_in_degree );

System.out.println( "sin(" + deg + ") = " + Math.sin( angle_in_radian ) ); }}

sin(45) = 0.7071067811865475

Some Commonly Used Math Class Members Math.toRadians( 270 )

Converts an angle measured in degrees to an approximately equivalent angle measured in radians.

Math.sin( 3.14159 ) A method giving us the trigonometric sine of an angle in

radian.

Math.sqrt( 2.25 ) A method giving us the positive square root of a value.

Lab Exercise: Using Math with if

Break Time – 15 minutes

They are for storing numbers with a decimal point.

They are for storing integers of different range limits.

Let's give the full list of the EIGHT Primitive Data Types in Java:

char boolean

double float

byte short int long

Java Primitive Data Types

What are Primitive Types? Eight build-in types in Java:

byte [-128 127]

short [-32768 32767]

int [-2147483648 2147483647]

long [-9223372036854775808 9223372036854775807 ]

float [±1038 with floating point]

double [±10308 with floating point]

char [‘A’, ‘B’, …, ‘a’, ‘b’, …, ‘0’, ‘1’, …, ‘!’, ‘#’]

boolean [true, false]

Java Primitive Data Types Variables in Java must bear a type.

Basically, we have these 8 types for declaring variables.

They are for storing different kind and different range of data.

The char Data Type char is one of the primitive types

representing a single character.

char aVariable;aVariable = 'a';

char gender = 'F';char grade = 'C';char symbol = '#';


Lab Exercise: Quadratic Equation Solver Java Primitive Data Types Java Class (Object) Types: Quick Revision Using the String Objects


Java Class (Object) Types The primitive data types are good for representing

simple data, such as a number, a character, a true/ false value.

In real life, information is usually not so simple.

Thus, we have to use some structured data types.

They are known as Class (Object) Types in Java.

Object-Oriented Programming Object-oriented Programming (OOP) is one of the

programming paradigms (school of thought, methodology) in computer science.

An object is used to store information as well as to keep methods for handling the information.

Synonyms: Object == Instance == Entity

Class ~= Static ~= Type

Customer

Customer

Bill

Customer

Customer

Michael

Account

Account

012-3-1441

Objects

Our world is full of objects.

Graphical representation of objects

Object ‘type’

Object name

Our world is full of objects.

Graphical representation of objects

Customer

Customer

Bill

Objects

Customer

Customer

Michael

Account

Account

012-3-1441

Modeling Our World We try to model this object world.

Objects can keep data/state and accomplish tasks. e.g.

A drink dispensing machine has a stock of 100 cans.A drink dispensing machine sells Coke.

Inhuman?! Certainly, but it helps us to program a computer in an

organized and manageable manner.

Classes A class (e.g., Customer) is a kind of mold or

template to create objects (e.g., Michael and Bill).

An object is an instance of a class. The object belongs to that class.

Customer

Customer

BillCustom

er

Customer

Michael

Customer

Customer

‘instance-of’/ ‘belongs-to’

Class Object

More Class/ Object Examples

PersonPerson

Michael

PersonPerson

Bill Gates

PersonPerson

Account

Account

019-9-5887AccountAccount

217-1-1345

Account

Account

Object-Oriented Programming We first define classes.

While the program is running, we may create objects from these classes.

We may store information in objects.

We send messages to an object, instruct it to perform a task.

(For example, we send a deposit $250.00 message to an Account object to add $250.00 into the account.)

Class (Object) Type Variables There are already lots of classes defined in the Java API.

Let’s see how to make use of them.String address;address = "CUHK, Shatin, HK";

File aFile;aFile = new File("Hello.zip");

ZipFile aZip;aZip = new ZipFile(aFile);

JButton aButton;aButton = new JButton("Ok");

Class (Object) Type Variables With classes and the objects we created from

the classes, we can represent, store and handle more complex form of data.

For example, we can represent some text using String, we can handle a ZIP file, we can process a JPEG image, we can show a button on the screen, etc.

Using the String Objects Usually, an object is created from a class using

the new( ) statement.

The String objects are different. They are privileged to use the double quotes for creation.

String address;address = "CUHK, Shatin, HK";

Using the String Object Methods There are many methods defined for String objects. We can easily find out some properties of a String.

String address;address = "CUHK, Shatin, HK";

char firstLetter;firstLetter = address.charAt(0);

int addressLength;addressLength = address.length();

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