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Object-Oriented Program Development
Using Java: A Class-Centered Approach,
Enhanced Edition
Objectives
You should be able to describe:
• Computer Science and Programming Languages
• Objects and Classes
• Constructing a Java Program
• The PrintStream Class’s print() and
println() Methods
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Objectives (continued)
• Using the javax.swing Package
• Programming Style
• Common Programming Errors
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Computer Science and Programming
Languages
• Information age
– Almost totally dependent and driven by
information technology
• Computer science
– Science of computers and computing
• Computer scientists
– Solve problems using scientific method
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Computer Science and Programming
Languages (continued)
• Fundamental areas of computer science:
–
–
–
–
–
Introduction to computer architecture
The Java programming language
Class development and design
Algorithm development
Introduction to data structures
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Programming Languages
• Computer program
– Self-contained set of instructions and data used to
operate computer to produce specific result
– Also called software
• Programming
– Process of developing and writing programs
• Programming language
– Set of instructions that can be used to construct
program
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Programming Languages (continued)
• Low-level languages
– Run on only one type of computer
– Machine language
• Sequence of binary numbers
– Assembly language
• Substitution of words for binary codes of machine
language
• Translated into machine language program before
being executed on computer
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Programming Languages (continued)
• High-level languages
– Use instructions that resemble natural languages
– Run on variety of computer types
– Examples:
•
•
•
•
•
Pascal
Visual Basic
C
C++
Java
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Programming Languages (continued)
• Source program
– Programs written in computer language
• Interpreted language
– Each statement translated individually
– Executed immediately upon translation
• Compiled language
– Translated as complete unit before any one
statement executed
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Programming Languages (continued)
• Java is both:
– Compiled
– Interpreted
• Java Virtual Machine
– Software program
– Reads bytecodes produced by compiler and
executes them
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Programming Languages (continued)
Figure 1.2: Translating a Java program
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Procedure and Object Orientations
• Procedure-oriented language
– Available instructions are used to create selfcontained units
• Object-oriented language
– Program must first define objects it will be
manipulating
• Java object-oriented
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Application and System Software
• Application software
– Programs written to perform particular tasks
required by users
• System software
– Collection of programs that must be readily
available to computer system for it to operate at all
– Operating system
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The Development of Java
• History:
–
–
–
–
–
–
FORTRAN
COBOL
BASIC
Pascal
C++
Java
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The Development of Java (continued)
• Web browser
– Program located and run on user’s computer to
display Web pages
– Java can run from Web browser
• Java provides:
– Cross-platform compatibility
– Write-once-run-anywhere
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The Development of Java (continued)
Figure 1.6: The two distinct Java environments
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Objects and Classes
• Objects
– Part of Java programming language as component
types
– Can be custom tailored by programmer
– Programmer can define custom objects
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A Class Is a Plan
• Structure for class of objects must be created at
start of programming process
• Class
– Explicitly written plan
– Complete set of parts and instructions needed to
create items
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From Recipe to Class
• Data declaration section
– Description of data to be used
• Methods section
– Defines how to combine data components to
produce desired result
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From Recipe to Class (continued)
Figure 1.11: A programming plan for address labels
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A First Java Class
• Class consists of:
– Class header line
• public class nameofclass
– Body
• Class body
– Encloses data and methods that make up class
– Typically two sections of code:
• Types of data that will be used
• Procedures that will be used on data
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A First Java Class (continued)
Figure 1.13: A sample Java class
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A First Java Class (continued)
Table 1.1: Java Class Components
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Constructing a Java Program
• Programs can use existing classes
• Java program:
– Considered executable applications program
– Class must contain method named main
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The main Method
• public static void main(String []
args)
• Every program must have main method
• Methods begin and end with {}
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The main Method (continued)
Figure 1.17: The structure of a main() method
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The main Method (continued)
Figure 1.18: The structure of a Java program
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Reserved Words
• Predefined by programming language for special
purpose
• Can only be used in specified manner for intended
purpose
• Also called keywords in Java
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Reserved Words (continued)
Table 1.2: Java Reserved Words
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Standard Identifiers
• Java-defined words with predefined purpose
– Can be redefined by programmer
• Names of classes and methods provided in Java
• Good programming practice
– Only use standard identifiers for intended purpose
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Standard Identifiers (continued)
Table 1.3: Subset of Java Standard Identifiers
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Identifiers
• Programmer-supplied words
• Common practice:
– First letter of each word capitalized
• Starting with second word
• Case sensitive
– identifiers TOTAL, total, and TotaL represent
three distinct and different names
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Identifiers (continued)
• Rules for identifiers:
– First character of identifier cannot be digit
– Only letters, digits, underscores, and dollar signs
may follow initial character
• Blank spaces not allowed
– Identifier cannot be reserved word
– Maximum number of characters in identifier name
unlimited
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What Is Syntax?
• Set of rules for formulating grammatically correct
language statements
• Program has proper form specified for compiler
• Individual statement or program can be
syntactically correct and still be logically incorrect
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The PrintStream Class’s print()
and println() Methods
• PrintStream class, methods:
– print()
– println()
– Display data to standard output
• Package
– One or more individual classes
– Stored in same directory
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The PrintStream Class’s print()
and println() Methods (continued)
• General syntax:
– objectName.print(data)
– System.out.print("Hello World!");
• Parameters
– Items passed to method through parenthesis
– Also called:
• Arguments
• Actual arguments
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The PrintStream Class’s print()
and println() Methods (continued)
• print()
– Prints output only
• println()
– Prints output and appends new line
• \n
– Newline escape character
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Java Documentation
• Sources for documentation:
– http//java.sun.com/docs/search.html
– Hard copy books:
• The Java Class Libraries
• JFC Swing Tutorial
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The System Class
• Provides methods for examining system-related
information such as:
– Name of operating system
– Java version number
• Supports basic input and output services
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Using the javax.swing Package
• Classes in package provide means of specifying
fully functional GUI with typical components such
as:
–
–
–
–
Check boxes
Data entry fields
Command buttons
Dialogs:
• Modal
• Modeless
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Using the javax.swing Package
(continued)
• JOptionPane.showMessageDialog(null,
"message", "title", icon-type);
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Using the javax.swing Package
(continued)
Figure 1.21: showMessageDialog() dialog boxes
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Using the javax.swing Package
(continued)
• Import statement
– Found at beginning of program after package
declaration
– Compiler searches for classes in packages listed for
import
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Static and Non-Static Methods
• Non-static
– Must be used with objects
– Examples:
• println()
• displayMessage()
– Syntax:
• objectName.methodName(arguments);
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Static and Non-Static Methods
(continued)
• Static
– Does not operate on object
– Receives all data as arguments
– Example:
• showMessageDialog()
– Syntax:
• ClassName.methodName(arguments);
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Programming Style
• Java ignores whitespace
• Proper programming style:
– Makes programs easy to read
– Minimizes mistakes
• Proper style for main method:
public static void main(String[]
args)
{
program statements in here;
}
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Comments
• Explanatory remarks made within program
• Comment types in Java:
– Line
– Block
• // Line comment
• /* Block comment
Spans lines */
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Common Programming Errors
• Knowing about common errors helps
programmers avoid them
• Most common errors:
– Forgetting to save program with same file name as
class name used within program
– Omitting semicolon at end of each statement
– Forgetting \n to indicate new line
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Summary
• Programming languages come in variety of forms
and types
• In object-oriented languages, basic program unit is
a class
– Java is object-oriented
• All Java classes use basic structure consisting of:
– Class header line
– Class body
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Summary (continued)
• Java program must have main() method
• PrintStream class provides two methods
print() and println()
– Used to display text and numerical results
• Java package consists of one or more individual
classes stored in same directory
– javax.swing package provides GUI classes
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