Java Fundamentals

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Java Fundamentals intro to the environment
Duke is the mascot of the Java language see a lot
of Duke at the official Java web site
http//www.java.sun.com/
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Java History

• Designed for computers embedded in consumer
  appliances
• Small, distributed, robust programs
• Which made it ideal for computing
• Wide variety of platforms
• Object oriented
• Multi-tasking
• Good memory management
• Basic syntax of C and C
• But, more object-oriented, excludes complex
  features
• James Gosling, (Canadian works at Sun
  Microsystems in 1999) developer still alive _at_
• http//java.sun.com/people/jag/

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Why Bytecode is Cool "write once, run
anywhere." when you compile your program, you
don't generate instructions for one specific
platform. generate Java bytecode, which are
instructions for the Java Virtual Machine (JVM).
Regardless of whether platform is Windows,
UNIX, Macros, or an Internet browser--has the JVM
it can understand those bytecodes.
Javas MagicThe Bytecode
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Object-Oriented Programming

• Code is organized in two ways
• around the code
• (what is happening)
• Around its data
• (who is being affected).OOPS

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Encapsulation

• Programming mechanism that binds together code
  and the data it manipulates
• Keeps both safe from outside interference and
  misuse
• When code and data are linked together in this
  fashion, an object is created, that supports
  encapsulation

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Encapsulation contd

• Javas basic unit of encapsulation is the class
• A class defines the form of an object
• Specifics both the data and the code that
  operates on that data
• Java uses a class specification to construct
  objects

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Encapsulation contd

• Code and data that constitute a class are called
  members of that class
• The data defined by the class are referred to as
  member variables
• Code that operates on that data is referred to as
  member methods or methods

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Polymorphismone interface, multiple methods

• Is the quality that allows one interface to
  access a general class of actions
• i.e. A steering wheel in a car, no matter what
  type of mechanism is used
• manual steering
• power steering
• rack-and-pinion steering
• steering wheel works the same

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Inheritance

• Which one object can acquire the properties of
  another object
• Red Delicious apple is part of the classification
  apple, which in turn is part of the fruit class,
  which is under the larger class food.
• A Red Delicious apple or MAC would in turn
  inherit its general attributes from its parents

food
fruit
meat
vegetables
apple
pear
orange
MAC
Red Delicious
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Multi-threaded, memory management

• Multi-threaded
• One program execs multiple threads
• Appear to run at same time
• Computing
• Reading disks
• Formatting display
• Transmitting over network

• Automatic memory recycling
• Lisp Smalltalk contribution
• Garbage collector
• Frees memory when finished with elements like
  class instances
• Avoid memory leaks

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Software Developers Kit (SDK)(older version
named JDK - Java Developers Kit )with JRE (Java
Runtime Environment)

• For home use must have a Java development system
  installed on your home computer
• Downloaded free of charge from www.java.sun.com
• Instructions for downloading and installing at
  home can be found on the course web page under
• General, Resources, Java..

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Using TextPad as your editor for entering java
code

• May use any editor (Notepad, TextPad, etc.)
• TextPad handy because can recognize java syntax
  colour coded statements, brackets, etc.
• Configure TextPad with links to SDK for easy
  access to java compile and run commands
• Instructions for downloading TextPad and
  installing at home can be found on the course web
  page under
• General, Resources, Java..

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Creating a Java Program

• Use TextPad, Notepad or another text editor
• not dependent on one-vendor environment
• Programs consist of
• One or more classes
• Programs name same as primary class
• Primary class has a main() method.
• The Java virtual machine (JVM) will execute main
  calls whatever else is needed.

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The Java 2 SDK on Disk

• Note that the Java SDK "home" directory is
  j2sdk1.4.?
•     It is common to store this location in an
  environment variable named java_home        
• set java_homej2sdk1.4.?
• Note these important subdirectories
• j2sdk1.4.?/bin
• j2sdk1.4.?/jre
• j2sdk1.4.?/lib

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SDK Tools

• In j2sdk1.4.?\bin on a Windows computer you will
  find
• javac.exe
• The Java compiler
• java.exe
• The Java interpreter
• More formally the Java Virtual Machine (JVM)
• javadoc.exe
• The Java documentation utility

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Hello World!
Use camel notation one exception Standard Class
names begin with a capital

• public class HelloWorld
• public static void main(String arg)
• System.out.println("Hello World!")
• Saved as "HelloWorld.java"

H
h
Be Careful When You Type Type all code,
commands, and file names exactly as shown. The
Java compiler and interpreter are case-sensitive,
so you must capitalize consistently. HelloWorld
?  helloworld
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Hello World!
Keyword class to declare that a new class is
being defined
main() method, line at which execution starts

• public class HelloWorld
• public static void main(String arg)
• System.out.println("Hello World!")
• Saved as "HelloWorld.java.page 18 in book

members of the class
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Compile/Run a Java program at DOS (command)
prompt

• Ensure JDK is on path
• set pathj2sdk1.4.?\binpath
• in autoexec.bat or another DOS batch file
• Invoke compiler
• javac HelloWorld.java
• produces file HelloWorld.class
• Invoke Java virtual machine
• java HelloWorld
• executes HelloWorld.class

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Compiling a Java program using TextPad
Missing "t in print.out
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Executing a Java Program using TextPad (after
fixing error)
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Comments in Java

• Same as JavaScript
• // everything in the line after this is ignored
• / this is a multi-line
• comment. Everything is
• ignored until /

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Javadoc - http//java.sun.com/j2se/javadoc/index.h
tmljavadocdocuments

• Javadoc is the tool from Sun Microsystems for
  generating API documentation in HTML format from
  doc comments in source code.
• For a sample of Javadoc-generated HTML, see J2SE
  1.4 API Documentation and
• J2SE 1.3 API Documentation.

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Javadoc from within TextPadTextPad in 2A206
will likely be configured with the following
tools already installed

• Add javadoc to the tools list
• Also handy if you add a tool to TextPad to make a
  .doc directory in the current directory. The
  javadoc tool puts the documentation in the .docs
  directory
• User may then run the mkdir tool once before
  running javadoc
• Instructions for configuring TextPad tools can be
  found on the course web page under
• General, Resources, Java..

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Javadoc comments(Appendix B page 551)

• The javadoc program takes as input your Java
  programs source file and outputs several HTML
  files that contain the programs documentation.
• Information about each class will be in its own
  HTML file.
• Javadoc will also output an index and a hierarchy
  tree.

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An Example that uses Documentation Commentspage
558

• After the beginning /, the first line or lines
  become the main description of your class,
  variable, or method.
• After that, you can include one or more of the
  various _at_ tags.
• Each _at_ tag must start at the beginning of a new
  line or follow an asterisk() that is at the
  start of a line.
• Multiple tags of the same type should be grouped
  together.

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Declaring Variables

• Identifier rules
• Names start with a letter
• Can contain letters or numbers
• _ and are "letters"
• Use Camel notation
• userName

• Variables are "typed"
• Fixed allocation of memory
• Value can change
• Type cannot change
• i.e. int cannot change to float
• declare variables before using

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Integer Declarations

• public class IntDeclares
• public static void main(String arg)
• int textCounter
• int wordCounter, lineCounter
• int docCounter0
• int fileCounter 0, driveCounter 0
• System.out.println("variable declared "
  driveCounter)
• One or more variables per declaration
• Must initialize value(s)
• Cannot use variables until initialized
• Even though default value is 0
• Note "" at end of every statement

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Java Keywords
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Primitive Variable Typesall others (string,
array, etc.) are reference types

• byte 1 byte integer (-128 to 127)
• char 2 bytes 1 character, can view as integer
• short 2 bytes integer (-32,768 to 32,767)
• Int(default) 4 bytes integer (2.147B)
• long 8 bytes integer (9,223,372T)
• float 4 bytes floating-point (9 sig digits,
  1045)
• Double(default) 8 bytes floating-point (18 sig
  digits, 10324)
• boolean logical true/false
• Note all are signed, except char and boolean

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Arithmetic Expressions

• Add x 1
• Subtract y 1
• Multiply x y
• Divide 15 / 6 produces 2
• 15.0 / 6.0 produces 2.5
• Modulus 15 6 produces 3
• (remainder in integer math)
• Expressions can contain multiple operators

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Arithmetic Precedence

• Brackets ()
• unary negation -3
• multiplication/division/modulus
• addition/subtraction
• assignment ()
• Note assignment has a "value"
• y (x 3) 2 // y has value 5
• All evaluated left-to-right
• Except assignment

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Relational Operators pg 63

• !
• gt
• lt
• gt
• lt

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Logical Operators pg 64

• Operator Meaning
• AND
• OR
• XOR (exclusive OR)
• Short-circuit OR
• Short-circuit AND
• ! Not

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Literals(constants or fixed values)

• By default, integer literals are of type int
• If you want to specify a long literal, append an
  l or an L.
• For example, 12 is an int, but 12L is a long
• By default, floating-point literals are of type
  double
• If you want to specify a float literal, append an
  f or an F to the constant.
• For example, 10.19F is of type float

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Character Escape Sequence
ch \t // this assigns ch the tab
character ch \ // assigns a single quote
to ch
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Demonstrate escape sequences in strings
class StrDemo public static void main(String
args) System.out.println(First
line\nSecond line System.out.println(A\tB\tC
) System.out.println(D\tE\tF)
use (new line) \n to generate a new line
use tabs(\t) to align output
Output First line Second line A B C D E F
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Initializing a Variable

• In general, you must give a variable a value
  prior to using it
• type var value
• Value is the value that is given to var when var
  is created
• int count 10 // give count an initial of 10
• char ch X // initialize ch with the
  letter X
• float f 1.25 // f is initialized with 1.2
• int a, b 8, c 19, d // b and c have
  initializations

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Type Conversion in Assignments

• When compatible types are mixed in an assignment,
  the value of the right side is automatically
  converted to the type of the left side as long as
  they are compatible which means
• The two types are compatible
• The destination type is larger that the source
  type
• int i
• float f
• i 10
• f i // OK to assign an int to a float
• For example boolean and int are not compatible
• double to long is not a widening conversion

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Casting Incompatible non-widening" Types
Casts (or "converts") a value to the specified
type.

• // Demonstrate casting
• class CastDemo
• public static void main(String args)
• double x, y
• byte b
• int i
• char ch
• x 10.0
• y 3.0
• i (int) (x / y) //cast double to int
• System.out.println("integer outcome of x / y
  " i)
• i 100
• b (byte) i
• System.out.println("Value of b " b)
• i 257
• b (byte) i
• System.out.println("Value of b " b)
• b 88

• Force value to a another type
• Example below (cast involves a narrowing
  conversion)
• double x, y
• (int) (x / y)
• Casting from double to int
• cast "i" to a correct type, then do math

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MaxVariablesDemo Programhttp//java.sun.com/docs
/books/tutorial/java/nutsandbolts/example-1dot1/Ma
xVariablesDemo.java
public class MaxVariablesDemo public static
void main(String args) // integers
byte largestByte Byte.MAX_VALUE
short largestShort Short.MAX_VALUE int
largestInteger Integer.MAX_VALUE long
largestLong Long.MAX_VALUE // real
numbers float largestFloat
Float.MAX_VALUE double largestDouble
Double.MAX_VALUE // other primitive
types char aChar 'S' boolean
aBoolean true // display them all
System.out.println("The largest byte value is
" largestByte) System.out.println("The
largest short value is " largestShort)
System.out.println("The largest integer value is
" largestInteger) System.out.println("T
he largest long value is " largestLong)
System.out.println("The largest float value is
" largestFloat) System.out.println("The
largest double value is " largestDouble)
if (Character.isUpperCase(aChar))
System.out.println("The character " aChar "
is upper case.") else
System.out.println("The character " aChar "
is lower case.")
System.out.println("The value of aBoolean is "
aBoolean)
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Results from MaxVariablesDemo Program
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Java Exercise

• There is an extensive online tutorial
  http//java.sun.com/docs/books/tutorial/index.html
  for Java. Follow the instructions in
• Your First Cup of Java (for Win32)
• Part 2 "Creating Your First Application" to
  create a simple "Hello, World" program. Work in a
  directory named g\WD1\exercise8.
• http//java.sun.com/docs/books/tutorial/getStarte
  d/index.html
• Follow the set of instructions from
• Getting Started
• Use TextPad or Notepad as instructed, pay careful
  attention to how the Java compiler (javac) and
  the Java Virtual Machine (java) are used.
• When done, open your "Hello, World" program with
  the TextPad editor. Use Tools gt Compile Java to
  compile your program. Note how TextPad calls
  javac for you. Next, use Tools gt Run Java
  Application to run your program. Note how TextPad
  calls java for you. For the rest of the course we
  will use TextPad, but you should know how to
  compile and run Java programs from the command
  line.

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Hello World - Applet

• http//java.sun.com/docs/books/tutorial/getStarted
  /cupojava/win32.html1

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Tutorial Questions and Answers

• http//java.sun.com/docs/books/tutorial/java/nutsa
  ndbolts/QandE/questions_operators.html

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To Do

• Read Module 1,2 and 3
• To My First Cup of Java HelloWorld exercise
• Do Assignment 1