Chapter 1: Introduction Object-Oriented Program Development Using Java: A Class-Centered Approach.

Chapter 1: Introduction

Object-Oriented Program Development Using Java:

A Class-Centered Approach

Object-Oriented Program Development Using Java: A Class-Centered Approach 2

Programming Languages

• Computer program

– A self-contained set of instructions and data used to operate a computer to produce specific results

– Also called software

• Programming is the process of developing and writing a program

• A programming language is a set of instructions that can be used to construct a program


Programming Languages (continued)

• Low-level languages:

– Machine language

– Assembly language



• High-level languages:– Use instructions that resemble natural languages

– Can be run on a variety of computer types

– Examples:

• Pascal

• Visual Basic

• C

• C++

• Java



• Source program

– Programs written in a computer language

• Interpreted language

– Each statement is translated individually and executed immediately upon translation

• Compiled language

– All statements are translated as a complete unit before any one statement is executed



• Java is both:

– Compiled

– Interpreted

• Java Virtual Machine

– Software program that can read bytecode produced by the compiler and execute it



Procedure and Object Orientations

• Procedure-oriented language

– Available instructions are used to create self-contained units

• Object-oriented language

– Program must first define objects it will be manipulating

• Java is object-oriented


The Development of Java

• History:

– Fortran

– COBOL

– BASIC

– Pascal

– C++

– Java


The Development of Java (continued)

• Web browser

– A program located and run on a user’s computer to display Web pages

– Java can run from a Web browser

• Java provides:

– Cross-platform compatibility

– Write-once-run-anywhere capability



Objects and Classes

• Objects

– Part of the Java programming language as component types

– Can be custom tailored by programmers

– Programmers can define custom objects


A Class Is a Plan

• The structure for a class of objects must be created at the start of the programming process

• Class

– Explicitly written plan

– Complete set of parts and instructions needed to create items


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



A First Java Class

• A class consists of a class header line and a body

• The class header line includes the words public class nameofclass

• Class body

– Encloses data and methods that make up class

– Typically two sections of code:

• The types of data that will be used

• Procedures that will be used on the data




Constructing a Java Program

• Programs can use existing classes

• A Java program is:

– Considered an executable applications program

– A class that must contain a method named main


The main Method

• public static void main(String [] args)

• Every program must have the main method

• Methods begin and end with {}



Reserved Words

• Predefined by programming language for special purpose

• Can only be used in specified manner for intended purpose

• Also called keywords in Java



Standard Identifiers

• Java-defined words that have predefined purpose

– Can be redefined by a programmer

• Names of classes and methods provided in Java

• A good programming practice is to only use standard identifiers for their intended purpose



Identifiers• Programmer-supplied words

• Can be made up of any combination of:– Letters

– Digits

– Underscores (_)

– Dollar signs ($)

• Common practice:– The first letter of each word, starting with the second

word in a multiword identifier, is capitalized


Rules for Identifiers in Java

• The first character of the identifier cannot be a digit

• Only letters, digits, underscores, and dollar signs may follow the initial character

– Blank spaces are not allowed

• Identifiers cannot be reserved words

• Maximum number of characters in the identifier name is unlimited


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


The PrintStream Class’s print()

and println() Methods• print() and println() are in the PrintStream class

and are print methods:

– Display data to standard output

• Package

– One or more individual classes stored in the same directory



and println() Methods (continued)

• General syntax:

– objectName.print(data)

– System.out.print("Hello World!");

• Parameters

– Items are passed to a method through parentheses

– Also called

• Arguments

• Actual arguments



and println() Methods (continued)

• print()

– Prints output only

• println()

– Prints output and appends new line

• \n

– Newline escape character


Java Documentation

• Sources for documentation:

– http//java.sun.com/docs/search.html

– Hard copy books:

• The Java Class Libraries

• JFC Swing Tutorial


The System Class

• Provides methods for examining system-related information, such as:

– Name of the operating system

– Java version number

• Supports basic input and output services


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;

}


Comments

• Explanatory remarks made within a program

• Comment types in Java:

– Line

– Block

• // Line comment

• /* Block comment

Spans lines */


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 the program

– Omitting a semicolon at the end of each statement

– Forgetting \n to indicate a new line

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Chapter 1: Introduction Object-Oriented Program Development Using Java: A Class-Centered Approach.

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