CSE Summer Preparatory Course

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CSESummer Preparatory Course

• Using the Java API

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Revision

• Introduction to Computers
• Introduction to Programming
• Introduction to Java a modern programming
  language
• Java Syntax Variables and Operations
• Basic Output
• Java Programming Lab and Exercise

Lecture 1
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Revision

• Getting User Input
• Storing Text Using String
• String Processing and Integer
• The boolean Data Type
• ifelse
• while-loop
• Swapping the value of two variables
• Java Programming Lab and Exercise

Lecture 2
Have you finished the problems in Lab 2?
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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

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The Java API

• System, String, JOptionPane, etc. are stuffs
  provided in the Java Application Programming
  Interface (API).

System.out.println(...)
String answer
JOptionPane.showInputDialog(...)
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The Java API Reference Manualhttp//java.sun.com/
j2se/1.5.0/docs/api/
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The Java API Reference ManualQuick Reference
Using NetBeans
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Importance of the Java API

• The Java language itself is already a strong
  programming tool.
• The API provides extra functionalities and tools,
  however.
• A single command using the API can perform
  enormous work for us.

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Using the Java API

• 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.

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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.

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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

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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.

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Using the Math Class
sin(45) 0.7071067811865475
class 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
) )
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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.

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Lab Exercise Using Math with if
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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

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Java Primitive Data Types

• Let's give the full list of the 8 Primitive Data
  Types in Java
• char boolean
• double float
• byte short int long

They are for storing numbers with a decimal
point.
They are for storing integers of different range
limits.
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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

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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.

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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 ''

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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

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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.

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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

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Objects

• Our world is full of objects.
• Graphical representation of objects

Object name
Object type
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Objects

• Our world is full of objects.
• Graphical representation of objects

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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.

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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.

Object
Class
instance-of/ belongs-to
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More Class/ Object Examples
217-1-1345
Account
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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.)

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Class (Object) Type Variables

• There are already lots of classes defined in the
  Java API.
• Lets 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")

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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.

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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

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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"

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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()

C
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Lab Exercise String Manipulation
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Any Enquiry?