Topic: Java in the Computer World

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Topic Java in the Computer World
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Computer Software vs. Hardware

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Programming languages

• High-level languages
• single statements could
• be written to accomplish
• substantial tasks.
• Assembly languages
• English-like abbreviations
• elementary operations
• Machine languages
• 1's and 0's
• machine-dependent

High-level language
Assembly language
Machine language 0111010
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Example (Programming languages)

• Machine languages
• 1300042774
• 1400493419
• 1200274027
• Assembly languages
• LOAD BASEPAY
• ADD OVERPAY
• STORE GROSSPAY
• High-level languages
• grossPay basePay overTimePay

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Java Software Development Environment

• You can have 4 separate parts
• Editor
• Compiler
• Interpreter
• Debugger
• Or you can combine some of these parts

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(No Transcript)
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Integrated Development Environment (IDE)

• IDE combins
• editor, compiler, interpreter and debugger
• IDE is a tool for developing software
• This course is not about IDE
• This course is about designing software

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Where is Java in the compter world? -- section
summary
High-level language
Assembly language
Machine language 0111010
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Topic Object Oriented Design

• Classes
• Methods

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Section I Classes
Classes

• Classification
• The classification process
• Classification is good
• Classification takes places in everyday life

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Classes -- How to classify
Classes

• Example
• object group gtclasses
• class monitor (output device)
• class printer (output device)
• class speaker (output device)
• class computer tower (computing device)
• class keyboard (input device)
• class mouse (input device)

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Class and Object Relation
Classes

• An object is an instance of a class
• A class represents a category of objects

obj
obj
Class monitor
Class printer
obj
obj
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Class and method relation
Classes
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Why Different Classes?
Classes

• Good thing about such modular design
• Independent objects gtlocal problem only
• Example
• bad keyboard, but everything else is still
  working fine
• Easy to find problems
• try a new keyboard --gt find out the old keyboard
  is bad
• Easy to fix problems
• buy a new keyboard for 15
• If the system does not have such modular design
• wed be in trouble.

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Sub-class
Classes

• A big class might have sub-classes
• Good vs. bad classification
• Example make sub-classes for books in a
  bookstore
• Good classification
• literature, arts, science, religion, sports,
  home, map
• Bad classification
• alphabetically order books section A,B,C...

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About Classes section summary
Classes

• We have learned
• Classification is good
• classification categorization
• (motivated why we want to split things into
  classes
• Good classification vs. bad classification
• Sometimes, a class has sub-classes

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About Classes section summary (continue)
Classes
obj

• Also, we have learned...
• An object is an instance of a class
• A method is inside of a class

Class monitor
obj
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Section II Methods
Methods

• Each method belongs to a class
• A class can have many methods

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Make Methods (Example)
Methods

• Example make up some methods for the printer
  class
• What does a printer do?
• Lets draw a flow chart...

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Methods
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Flow chart --gt Methods
methods

• Flow chart
• help us to think through
• breaks big task to smaller sub-tasks
• small sub-tasks gt methods
• Each method is an action
• Now, we are ready to write the skeleton of class
  printer...

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• //------------------------------------
• // class Printer
• //------------------------------------
• class Printer
• //---------------------------
• // define variables
• //---------------------------
• boolean double_sided // The
  variable "double_sided"
• 
  // as type "boolean", so it can
• 
  // take only values "true" or "false".
• int maximum_memory_size // The maximum
  size of the memory
• 
  // is an integer. Type "int"integer.
• //-------------------------------------
• // Method receive_file
• // DOES Receive files to be printed.
• //--------------------------------------
• void receive_file()

methods
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About Methods section summary
methods

• In this section, we learned that
• A class consists of many/some methods
• A class might have methods to handle some tasks
• Break a big task into small sub-tasks
• method sub-tasks (manageable sub-tasks)
• often, mehtods gt an action

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Topic Summary Class and method

• Class ltgt classification
• class ltgt modular design
• class (method) (method)
• big task (small sub-task) (small sub-task)
  ...
• Methods ltgt small sub-task
• We are happy -- that we designed a nice schematic
  Printer class.

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Programming process

ideas
Program text, on paper or in head
Work done at the keyboard with a text editor
Compiler-- a program for translating programs
Program in Java byte code, in the file
Test.class
Program text, in a file such as Test.java
Java Virtual Machine JVM, executes the program
Test.class