Java Programming Fifth Edition

Learning About Programming • Program – Set of written instructions that tells computer what to do

Java Programming Fifth Edition

• Machine language – Most basic circuitry-level language – Low-level programming language

• High-level programming language – Allows you to use vocabulary of reasonable terms

• Syntax – Rules of language

Chapter 1 Creating Your First Java Classes

• Program statements – Similar to English sentences – Carry out tasks of program

Java Programming, Fifth Edition

Learning About Programming (continued)

Introducing Object-Oriented Programming Concepts

• Compiler or interpreter

• Procedural programming

– Translates language statements into machine code

– Sets of operations executed in sequence – Variables

• Syntax error

• Named computer memory locations that hold values

– Misuse of language – Misspelled programming language word

– Procedures • Individual operations grouped into logical units

• Debugging

• Object-oriented programs

– Freeing program of all errors

– Create classes – Create objects from classes – Create applications

• Logic errors – Also called semantic errors – Incorrect order or procedure Java Programming, Fifth Edition

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Introducing Object-Oriented Programming Concepts (continued)

Understanding Objects and Classes • Objects

• GUI system

– Made up of attributes and methods

– Allows you to treat files as objects – Not all object-orientated programs written to use GUI

• Object-oriented programming differs from traditional procedural programming – Basic concepts

– Characteristics that define object – Differentiate objects of same class – Value of attributes is object’s state

• Class

• Encapsulation • Inheritance • Polymorphism


• Attributes

– Describes objects with common properties – Definition – Instance 5

Understanding Objects and Classes


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Understanding Objects and Classes (continued) • Method – Self-contained block of program code – Similar to procedure

• Encapsulation – Refers to hiding of data and methods within object – Provides security – Keeps data and methods safe from inadvertent changes

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Learning About Java

Understanding Inheritance and Polymorphism

• Java – – – –

• Inheritance – Important feature of object-oriented programs – Classes share attributes and methods of existing classes but have more specific features – Helps you understand real-world objects

Developed by Sun Microsystems Object-oriented language General-purpose Advantages • Security features • Architecturally neutral

• Java (continued) – Can be run on wide variety of computers – Does not execute instructions on computer directly – Runs on hypothetical computer known as Java virtual machine (JVM)

• Polymorphism – Means “many forms” – Allows same word to be interpreted correctly in different situations based on context

• Source code – Programming statements written in high-level programming language


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Learning About Java (continued)

Learning About Java (continued) • Bytecode – Statements saved in file – Java compiler converts source code into binary program

• Java interpreter – Checks bytecode and communicates with operating system – Executes bytecode instructions line by line within Java virtual machine


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Analyzing a Java Application That Uses Console Output

Java Program Types • Applets

• Even simplest Java application

– Programs embedded in Web page

– Involves fair amount of confusing syntax

• Java applications

• Print “First Java application” on screen

– Called Java stand-alone programs – Console applications • Support character output

– Windowed applications • Menus • Toolbars • Dialog boxes

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Understanding the Statement That Prints the Output (continued)

Understanding the Statement That Prints the Output • Literal string – Will appear in output exactly as entered – Written between double quotation marks

• Arguments – Pieces of information passed to method

• Method – Requires information to perform its task


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Understanding the First Class (continued)

Understanding the First Class • Everything used within Java program must be part of a class • Define Java class using any name or identifier • Requirements for identifiers

• Requirements for identifiers – Can only contain: • • • •

– Must begin with: • Letter of English alphabet • Or non-English letter (such as

or )

Letters Digits Underscores Dollar signs

– Cannot be Java reserved keyword – Cannot be true, false, or null

– Cannot begin with digit

• Access modifier – Defines how class can be accessed Java Programming, Fifth Edition

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Understanding the First Class


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Understanding the main() Method • static – Reserved keyword – Means method accessible and usable • Even though no objects of class exist

• void – Use in main() method header – Does not indicate main() method empty – Indicates main() method does not return value when called – Doesn’t mean main() doesn’t produce output 21


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Adding Comments to a Java Class

Shell Code

• Program comments – Nonexecuting statements added to program for documentation – Use to leave notes for yourself or others – Include author, date, class’s name or function

• Comment out a statement – Turn it into a comment – Compiler does not translate and the JVM does not execute its command


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Adding Comments to a Java Class (continued)


• Types of Java comments

• Types of Java comments (continued)

– Line comments

– Javadoc comments

• Start with two forward slashes (//)

• Special case of block comments • Begin with slash and two asterisks (/**) ( ) • End with asterisk and forward slash (*/)

• Continue to end of current line • Do not require ending symbol

– Block comments

• Use to generate documentation

• Start with forward slash and asterisk (/*) • End with asterisk and forward slash (*/)


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Saving, Compiling, and Running and Modifying a Java Application


• Saving a Java class – Save class in file with exactly same name and.java extension • For public classes • Class name and filename must match exactly

• Compiling a Java class – Compile source code into bytecode – Translate bytecode into executable statements • Using Java interpreter

– Type javac First.java Java Programming, Fifth Edition

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Saving, Compiling, and Running and Modifying a Java Application (continued) • Compilation outcomes

Running a Java Application • Run application from command line

– javac unrecognized command

– Type java First

– Program language error messages – No messages indicating successful completion

• Shows application’s output in command window • Class stored in folder named Java on C drive

• Reasons for error messages – Misspelled command javac – Misspelled filename – Not within correct subfolder or subdirectory on command line – Java not installed properly Java Programming, Fifth Edition

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Running a Java Application (continued)


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Modifying a Java Class • Modify text file that contains existing class • Save file with changes – Using same filename

• Compile class with javac command • Interpret class bytecode and execute class using java command


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Creating a Java Application Using GUI Output

Creating a Java Application Using GUI Output (continued)

• JOptionPane – Produce dialog boxes

• Dialog box – GUI object resembling window – Messages placed for display

• Package

– Group of classes

• import statement – Use to access built-in Java class 33

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Correcting Errors and Finding Help (continued)

Correcting Errors and Finding Help • First line of error message displays:

• Parsing

– Name of file where error found – Line number – Nature of error

– Process compiler uses to divide source code into meaningful portions

• Logic error

• Next lines identify:

– Syntax correct but produces incorrect results when executed – Usually more difficult to find and resolve

– Symbol – Location

• Compile-time error

• Java API

– Compiler detects violation of language rules – Refuses to translate class to machine code Java Programming, Fifth Edition


– Also called the Java class library – Prewritten Java classes 35


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