Chapter 8: Introduction to
High-Level Language
Programming
Invitation to Computer Science,
Java Version, Third Edition
Objectives
In this chapter, you will learn about

Where do we stand?

High-level languages

Introduction to Java

Virtual data storage

Statement types
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Objectives (continued)

Meeting expectations

Managing complexity

Object-oriented programming

Graphical programming

The big picture: Software engineering
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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


Class header


Announces that a class is about to be defined
Class


Give information to human readers of code
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 user’s 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


Conditional


Instructions are executed in order
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


nonvoid method


Does not pass any value back to the main 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


Frame buffer


The screen is made up of thousands of individual
picture elements, or pixels, laid out in a twodimensional grid
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


Abstract Windowing Toolkit (AWT)


Contains a collection of software routines that
control the setting and clearing of pixels
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
Invitation to Computer Science, Java Version, Third Edition
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Figure 8.36
Steps in the Software Development Life Cycle
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Scaling Up

Programs written by students


Real-world programs


No longer than a few hundred lines
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
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