Beginning Java and/or J# and/or C#

Dr. Burns

About this course, Instructor A first course in computer languages Which language?? Your instructor is familiar with Visual Basic

Java, C# and C++

How to reach me?? Office hrs: 11-11:45 T Th Office phone: 742-1547 Email: jburns.@ba.ttu.edu Website: http://burns.ba.ttu.edu

Pedagogical Requirements 2 exams, each worth 20% 1 project worth 20% Homework worth 20% Presentations worth 20%

Students will be asked to present material in class five times during the semester

Some 3-hour classes are organized as…

1.5 hours of lecture by me (80-90 min) 1.5 hr lecture by one of you

.75 hr by one student (40 min) .75 hr by another student (40 min)

A bit of History Java was developed at Sun Microsystems

by a programmer named James Gosling who originally had in mind a language to control robots

June 1991 to 1995 was the development period

It is platform-independent and will run on any operating system or computer

More Java history Development goals were to create a

language with a C/C++ like syntax, but with WORA (Write Once, Run Anywhere)

The language was also made much simpler than C++ No pointer variables, no pointer arrays, no

destructors, etc.

Java Standard The Java standard is a de facto standard

(not one that is controlled by ANSI or ISO) that is controlled by the Java Community Process

Java Language Goals It should be object-oriented It should allow the same program to be executed

on multiple operating systems and microprocessors using different machine languages

It should contain built-in support for use of computer networks

It should be executable from remote sources It should be easy to use (Wikipedia)

J# Programming language A transitional language to assist Java

programmers to transition to Microsoft’s .NET platform

J# can work with Java bytecode as well as source, so it can be used to transition applications that use 3rd-party libraries

It was developed by the Hyderabad-based Microsoft India Development Center at HITEC City in India

Fundamental differences between J# and Java Both use the same general syntax There are non-Java conventions in J# to

support the .NET environment J# does not compile Java language source

code to Java bytecode and does not support Java applet development or the ability to host applets directly in a web browser

Future of J# J# is not considered a language on a par

with C# or VB.NET and does not have the same level of support, samples or updates as the other languages do

Nevertheless, J# is a usable .NET language and has access to all the CLR features

What is CLR? CLR stands for Common Language

Runtime and is the virtual machine component of Microsoft’s .NET platform. It is Msft’s implementation of the Common Language Infrastructure (CLI) standard.

Developers using the CLR write code in a language such as C# or VB.Net.

History of J# J# is Microsoft’s version of Java J# will run only on Windows machines Uses different methods names than Java Within Visual Studio, it can be mixed and

matched with Visual C++, Visual Basic, Visual C#, ASP.net, etc.

Which language works best for your needs?

Let me suggest Java or Visual C#

Reserved Words/Objects in C# or Java

Only about 48 of them, compared to over 200 in Visual Basic

Is Object-oriented But doesn’t support pointer variables, nor is

the programmer allowed to destroy objects, unlike C++

Reserved Words abstract assert boolean break byte case catch char const

continue default do double else enum extends final

More reserved words finally float for goto if implements import instanceof int

interface long native new package private protected public return

Still more reserved words short static strictfp super switch synchronized this

throw throws transient try void volatile while

Notice…. None of the reserved words begins with an

uppercase character (both C# and Java have case sensitive identifiers)

The reserved words shown in RED are also C# reserved words

C# has 75 reserved words (listed on page 31 of your text)

Identifiers These are words you choose for…

Class libraries (Java) Classes Namespaces (C#) Variables Methods They cannot be reserved words

More on Identifiers Class names should start with uppercase Method and variable names should start

with lower case No spaces You can only use letters (lower and

uppercase), digits and the underscore character

Some bad class names An employee Space char is

bad Inventory Item Space char is bad Class a reserved word 2009Budget can’t begin with digit Phone# # is illegal

Operators Supports only the basic operators

! {the logical NOT} * / % {multiplication, division, modulus} + - {addition, subtraction} > < >= <= {Relational} == != {Equality} && {Logical AND} || {logical OR}

Operators in C++ that are not supported

++ --

Many others

Object Technology Inheritance -- gives rise to REUSE Encapsulation

Information hiding Polymorphism Contains attributes (data and methods) Objects are called classes No support for procedural programming—which is

the direct opposite to object-oriented programming

Class—an object Encapsulates both data and behaviors Behavior is delineated with a method—a

collection of code Consider the class Sedan(…) Contained within it are constants like

Wheels = 4, chassis = 1, engine = 1, doors = 4 Color = RED

The class Sedan() has methods that describe its behaviors Accelerates(…) Slows_down(…) Consumes_gas(…) Creates_pollution(….)

Each of these is a method, a collection of code that acts as a group to produce the behavior

Method A self-contained block of program code,

similar to a procedure or subroutine

Procedural vs. Object-oriented programming

Procedural programming What I did using Fortran as a software engineer

working for the Boeing Company in the 1970’s Just long lists of code

Object-oriented programming—organizes code into objects—allows for reuse

The generic structure for an Object First, a list of all the possible header

declarations—to support polymorphism Second, a list of all the data types and their

initializations Third, a list of all the methods, coupled with

their code declarations

Objects and their instantiations OBJECT INTSTANTIATION truck fordF150 automobile chevyMalibu animal dog

Header declarations—the same in Java and C#

Java: public static void main(String[] args) C#: static void main(String[] args) public static void main(String[] args)

Notice—no semicolon after header dec

What is main(String[] args)? Is it a class? Is it an instance of a class? Is it a method? Is it a function?

What do the reserved words mean? public—the method is accessible to

everyone, not just other methods inside the class

static—the method stays alive and functional while the program is running

void—the method does not return a value through its name

Instantiations We use the keyword ‘new’ to create an

instantiation of an object: New automobile Toyota

Here Toyota is an instance of the class automobile

Inheritance The ability of a class to inherit the data and

methods of another previously defined class.

my1997ToyotaCorolla() extends Sedan()_ Inherits all of the data and methods of

Sedan()—reuses them—they don’t have to be redefined

Polymorphism Literally means ‘many forms’ Allows methods to be used differently in

different contexts Run() can be a footrace, an execution of a

computer program, or a business process It is correctly understood in context The method eat() will be different depending on

what kind of animal is eating

Code for a Class

Public class First

{

public static void main(String[] args)

{

System.out.println(“First Java app”);

}

}

The Membership Operator Is simply the . Examine……………System.out.println(“First Java app”); We see that println() is a method within a

class out which is a class within a class called System

Unfortunately, J# and C# do not use these names

What is (“First Java app”)? “First Java app” is a literal string of

characters – placed within double quotes This string is an argument of the method System.out.println() Methods are always followed by ()

parentheses What is placed within those parentheses

are called arguments

Some TLA’s—Three-letter Acronyms IDE – Integrated Development Environment JVM – Java Virtual Machine JRE – Java Runtime Environment SDK—Software Development Kit API—Application Programming Interface CLR—Common Language Runtime (Microsoft)

is part of .NET WPF—Windows Presentation Foundation

Integrated Development Environments

IDE – Integrated Development Environment—what Visual Studio and Eclipse provide—usually consisting of editor, parser, interpreter

But sometimes the IDE is capable of compiling and linking—creating a stand alone executable– ending with .exe

What is the sequence leading to execution?

In any language, it is1. Enter code in the editor– editor checks for

errors -- result is a text file with the extension of .java or .J#

2. Compile code into machine language – result is a binary file with the extension .bin

3. Link code to other compiled objects to create a stand alone executable – result is a binary file with the extension .exe

There are many variations on this sequence ….

Enter code – check for errors -- IDE saves the result as a text file.

IDE does a ‘quick’ interpret and execute without creating a stand alone executable

What is the difference between interpretation and execution? No difference as far as the output of the

program is concerned. With interpretation, a line of source code is

interpreted and executed without its being compiled, linked and executed as a stand alone module

This is very slow compared to stand alone execution

Microsoft .NET

Common Language Runtime diagram

What about the sale of commercial products?

Do you want these products interpreted or executed from a stand alone executable?

Java Compilations Java compilers typically produce bytecode

rather than binary (machine language) This makes them platform independent JVM’s and JRE’s then interpret the byte

codes upon execution Because of this, Java programs run slower

than native executables

Freeware A Java IDE (Java SE 6) that is free can be

found at http://java.sun.com A Java JRE that is free can be found at

http://java.sun.com A downloadable Java Tutorial is available

at http://java.sun.com/docs/books/tutorial/

What about Applets? Applets are scripts, segments of Java code

that get passed down with a web page. Your browser has a Java interpreter that executes the code line by line, creating the animation in a box of the page

Comments // the entire line is a comment /* begins a comment that can continue over

several lines and ends with */ this I s called a block comment

C# supports all of the above /** is a Javadoc comment that works with a

special documentation program; must end with */

More sample programsImport Javax.swing.JOptionPane;

Public class FirstDialog

{

public static void main(String{} args)

{

jOptionPane.showMessageDialog(null,”First Java dialog”);

System.exit(0);

}

}

Data type Declarations Specify the type of data and the length of

the data item in bytes int, short, long float, double boolean enum

Floating Point Representation Internal representation Floating-point numbers are typically packed into a

computer datum as the sign bit, the exponent field, and the significand (mantissa), from left to right. For the IEEE 754 binary formats they are apportioned as follows:

TypeSignExponentExponent biassignificandtotalHalf (IEEE 754-2008)15151016Single181272332Double11110235264Quad11516383112128

Data Types -- Integer Int – the default declaration – 4-byte integer Short—2-byte integer Long—8-byte integer

Floating Point Float—a 4-byte floating point number Double—an 8-byte floating point number