Chapter 8: Introduction to High-Level Language Programming

1
Chapter 8 Introduction to High-Level Language
Programming

• Invitation to Computer Science,
• Java Version, Third Edition

2
Objectives

• In this chapter, you will learn about
• Where do we stand?
• High-level languages
• Introduction to Java
• Virtual data storage
• Statement types

3
Objectives (continued)

• Meeting expectations
• Managing complexity
• Object-oriented programming
• Graphical programming
• The big picture Software engineering

4
Where Do We Stand?

• Early days of computing
• Programmers were satisfied with assembly language
• Programs mostly written by very technically
  oriented people
• Later decades
• Programmers demanded a more comfortable
  programming environment
• Programs were now also written by nontechie
  people

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High-Level Languages

• High-level programming languages
• Called third-generation languages
• Created to overcome deficiencies of assembly
  language
• Expectations of a high-level language program
• The programmer need not manage the details of the
  movement of data items within memory nor exactly
  where those items are stored

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High-level Languages (continued)

• Expectations of a high-level language program
  (continued)
• Programmer can take a macroscopic view of tasks
  primitive operations can be larger
• Program will be portable
• Programming statements will be closer to standard
  English and use standard mathematical notation

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Introduction to Java A Simple Java Program

• Comments
• Give information to human readers of code
• Class header
• Announces that a class is about to be defined
• Class
• A collection of methods
• Method
• A section of code that performs a service

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• Figure 8.2 A Simple Java Program

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Running a Java Program

• File containing the Java code
• Same name as the class
• File extension .java
• Example TravelPlanner.java
• Running a Java program
• Program compiled
• Example File TravelPlanner.class created
• Translation to object code completed program
  linked, loaded, and executed

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Virtual Data Storage

• Identifiers
• Names in a programming language
• Keyword
• Has a special meaning in Java
• Java is a case-sensitive, free-format language
• Variable
• A named location in memory
• Must be declared before it can be used

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• Figure 8.4
• Some of the Java Primitive Data Types

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Virtual Data Storage (continued)

• An array
• Groups together a collection of memory locations,
  all storing data of the same type

Figure 8.5 A 12-Element Array Hits
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Statement Types

• Input/output statements
• Input statement
• Collects a specific value from the user for a
  variable within the program
• Output statement
• Writes a message or the value of a program
  variable to the users screen or to a file

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Statement Types (continued)

• Assignment statement
• Assigns a value to a program variable
• Control statement
• Directs the flow of control
• Can cause it to deviate from the usual sequential
  flow

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Input Statements

• A prompt
• A message that tells the user what kind of input
  the program wants
• Console class
• Not a standard Java class written for this book
• Can be used to handle both the prompt and the
  retrieval of the value in one statement

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Input Statements (continued)

• Methods
• readInt
• readDouble
• readChar
• Syntax
• variable1 Console.readInt(prompt)
• variable2 Console.readDouble(prompt)
• variable3 Console.readChar(prompt)

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Output Statements

• Output to the screen
• System.out.println(string)
• The string can be
• Empty
• System.out.println()
• Literal string
• System.out.println("Here's your answer." )
• Composed of two or more items
• System.out.println("Give me" 5)

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The Assignment Statement

• General form
• variable expression
• Expression is evaluated first the result is
  written into the memory location specified on the
  left

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The Assignment Statement (continued)

• Examples
• B 2
• Suppose that B is an integer variable
• A B C
• Suppose that A, B, and C are integer variables
• Letter 'm'
• Suppose that Letter is a variable of type char

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Control Statements

• Types of control mechanisms
• Sequential
• Instructions are executed in order
• Conditional
• The choice of which instructions to execute next
  depends on some condition
• Looping
• A group of instructions may be executed many times

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Control Statements (continued)

• Sequential is default mode of execution
• Conditional flow of control
• Evaluation of a Boolean condition (also called a
  Boolean expression)
• The programming statement to execute next is
  based on the value of the Boolean condition (true
  or false)

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Control Statements (continued)

• Conditional flow of control (continued)
• if-else statement
• if (Boolean condition)
• S1
• else
• S2
• if variation of the if-else statement
• if (Boolean condition)
• S1

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• Figure 8.10
• Conditional Flow of Control
• (If-Else)

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• Figure 8.11
• If-Else with Empty Else

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Control Statements (continued)

• Looping (iteration)
• The loop body may be executed repeatedly based on
  the value of the Boolean condition
• while statement
• while (Boolean condition)
• S1

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• Figure 8.13
• While Loop

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Meeting Expectations

• Java meets the four expectations for a high-level
  programming language
• Expectations
• The programmer need not manage the details of the
  movement of data items within memory nor pay any
  attention to where specifically they are stored

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Meeting Expectations (continued)

• Expectations (continued)
• The programmer can take a macroscopic view of
  tasks, thinking at a higher level of problem
  solving
• Programs written in high-level languages will be
  portable rather than machine-specific
• Programming statements in a high-level language
• Will be closer to standard English
• Will use standard mathematical notation

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Managing Complexity Divide and Conquer

• Divide and conquer
• Divide the problem into small pieces
• In a computer program
• Divide the code into modules or subprograms, each
  of which does some part of the overall task
• Empower these modules to work together to solve
  the original problem

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• Figure 8.20 Structure Charts

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Using Methods

• Method
• A module of code in Java
• Named using ordinary Java identifiers
• By custom, name starts with a lowercase letter

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Using Methods (continued)

• Two types of methods
• void method
• Does not pass any value back to the main method
• nonvoid method
• Returns a single new value back to the main
  method
• Overall form of a method invocation
• class-identifier.method-identifier(argument list)

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Writing Methods

• General form of the method header
• scope-indicator return-indicator
  identifier(parameter list)
• Arguments in Java are passed by value
• A variable declared within a method can be used
  only within that method
• Return statement
• Syntax
• return expression

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• Figure 8.27
• Some Java Terminology

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Object-Oriented Programming What Is It?

• Object-oriented programming (OOP)
• A program is a simulation of some part of the
  world that is the domain of interest
• Each object is an example drawn from a class of
  similar objects
• Key elements of OOP
• Encapsulation
• A class consists of its subtask modules and its
  properties, and both components are
  encapsulated with the class

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What Is It? (continued)

• Key elements of OOP (continued)
• Inheritance
• Once a class A of objects is defined, a class B
  of objects can be defined as a subclass of A
• Polymorphism
• One name, the name of the service to be
  performed, has several meanings, depending on the
  class of the object providing the service

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Java and OOP

• Java is an object-oriented programming language
• Static method
• Can be invoked by giving the class name, a dot,
  the method name, and a list of arguments
• Objects Instances of a class
• Instance variables Properties
• Instance methods Services

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Java and OOP (continued)

• Syntax to request an object to invoke a method
• object-identifier.method-identifier(argument
  list)
• Calling object
• The object that invokes a method

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What Have We Gained?

• Two major advantages of OOP
• Software reuse
• A more natural world view

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Graphical Programming Graphics Hardware

• Bitmapped display
• The screen is made up of thousands of individual
  picture elements, or pixels, laid out in a
  two-dimensional grid
• Frame buffer
• Memory that stores the actual screen image
• Terminal hardware displays the frame buffer value
  of every individual pixel on the screen

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• Figure 8.34
• Pixel Numbering System in a Bitmapped Display

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Graphics Software

• Graphics library
• Contains a collection of software routines that
  control the setting and clearing of pixels
• Abstract Windowing Toolkit (AWT)
• Contains routines that allow users to create
  powerful interfaces
• Swing components
• Even more powerful GUI components than AWT

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Graphics Software (continued)

• Graphics class
• Contains drawing commands that allow you to
• Draw geometric shapes (lines, rectangles, ovals,
  polygons, and so on)
• Set, change, and define colors
• Fill in or shade objects
• Create text in a range of fonts and sizes
• Produce graphs and charts

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The Big Picture Software Engineering

• Software life cycle
• The overall sequence of steps needed to complete
  a large-scale software project
• Implementation represents a relatively small part
  of the cycle

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• Figure 8.36
• Steps in the Software Development Life Cycle

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Scaling Up

• Programs written by students
• No longer than a few hundred lines
• Real-world programs
• 2, 3, or 4 orders of magnitude larger
• Large-scale software development
• Extensive planning and design needed
• A team of programmers needed
• Software engineering

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The Software Life Cycle

• Each step in the software development life cycle
• Has a specific purpose and activities
• Should result in a written document
• The feasibility study
• Problem specification
• Program design

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The Software Life Cycle (continued)

• Algorithm selection or development, and analysis
• Coding
• Debugging
• Testing, verification, and benchmarking
• Documentation
• Maintenance

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Modern Environments

• Integrated Development Environment (IDE) speeds
  program development by providing
• A text editor
• A file manager
• A compiler
• A linker and loader
• Tools for debugging

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Summary

• In a high-level language, the programmer
• Need not manage storage nor movement of data
  values in memory
• Can use more powerful program instructions that
  are more like natural language
• Can write a much more portable program
• Java is an object-oriented, high-level
  programming language

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Summary (continued)

• In Java, an if-else statement can be used to
  create a conditional flow of control
• In Java, a while loop can be used for iteration
• Software life cycle Overall sequence of steps
  needed to complete a large-scale software project