Java Programming

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Prof. Moheb Ramzy Girgis

Department of Computer Science Faculty of Science

Minia University

1. Introduction to Programs and Java

Java Programming - Prof. Moheb Ramzy Girgis Dept. of Computer Science - Faculty of Science

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Programs



Computer

programs

, known as

software

, are

instructions to the computer.



You tell a computer what to do through programs.

Without

programs,

a

computer

is

an

empty

machine.



Computers do not understand human languages, so

you

need

to

use

computer

languages

to

communicate with them.



Programs are written using programming

languages.

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Programming Languages

 Machine language is a set of primitive instructions built into every computer. The instructions are in the form of binary code, so you have to enter binary codes for various instructions. Program with native machine language is a tedious process. Moreover the programs are highly difficult to read and modify.

 For example, to add two numbers, you might write an instruction in binary like this:

1101101010011010

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Machine Language Assembly Language High-Level Language

Programming Languages



Assembly

languages

were

developed

to

make

programming

easy.

Since

the

computer

cannot

understand assembly language, however, a program

called assembler is used to convert assembly language

programs into machine code.



For example, to add two numbers, you might write an

instruction in assembly code like this:

ADDF3 R1, R2, R3

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Programming Languages



The high-level languages are English-like and easy

to learn and program. For example, the following is

a high-level language statement that computes the

area of a circle with radius 5:

area = 5 * 5 * 3.1415;

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Machine Language Assembly Language High-Level Language

 COBOL (COmmon Business Oriented Language)

 FORTRAN (FORmula TRANslation)

 BASIC (Beginner All-purpose Symbolic Instructional Code)

 Pascal (named for Blaise Pascal)

 Ada (named for Ada Lovelace)

 C

 Visual Basic (Basic-like visual language developed by

Microsoft)

 Delphi (Pascal-like visual language developed by Borland)

 C++ (an object-oriented language, based on C)

 C# (developed by Microsoft for developing applications

based on the Microsoft .NET platform)

 Java (developed by Sun Microsystems)

Popular High-Level Languages

Java Programming - Prof. Moheb Ramzy Girgis

Dept. of Computer Science - Faculty of Science Minia University

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Compiling Source Code



A program written in a high-level language is called a

source program

.



Since

a

computer

cannot

understand

a

source

program. Program called a

compiler

is used to translate

the source program into a machine language program

called an

object program

.



The object program is then linked with other supporting

library code to form an

executable file

, which can be

run (executed) on the machine.

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Why Java?

 Java is a general purpose programming language.

 It enables users to develop and deploy applications on the

Internet for servers, desktop computers, and small hand-held devices.

 The future of computing is being profoundly influenced by

the Internet, and Java promises to remain a big part of that future.

 Java is the Internet programming language.

 Java programs can be run from a Web browser. Such

programs are called applets. Applets employ a modern graphical interface with buttons, text fields, text areas, radio buttons, and so on, to interact with users on the Web and process their requests.

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Why Java? (Continued)

 Java can be used to develop Web applications.

 Java can also be used to develop applications for

hand-held devices such as cell phones.

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Java Development Tools

 Java comes in three editions: Java Standard Edition (Java

SE), Java Enterprise Edition (Java EE), and Java Micro Edition (Java ME).

 Java SE can be used to develop client-side standalone

applications or applets.

 Java EE can be used to develop server-side applications,

such as Java servlets and JavaServer Pages.

 Java ME can be used to develop applications for mobile

devices, such as cell phones.

Java Development Tools (Continued)

 In this course we will use Java SE to introduce Java

programming.

 There are many versions of Java SE. The latest is Java SE 8.  _{Sun releases each version with a}Java Development Toolkit

(JDK). For Java SE 8, the Java Development Toolkit is called JDK 1.8 (JDK 8).

 JDK consists of a set of separate programs, each invoked

from a command line, for developing and testing Java programs.

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 Besides JDK, you can use a Java development tool (e.g., NetBeans, Eclipse, and TextPad)—software that provides an integrated development environment (IDE) for rapidly developing Java programs.

 Editing, compiling, building, debugging, and online help

are integrated in one graphical user interface. Just enter source code in one window or open an existing file in a window, then click a button, menu item, or function key to compile and run the program.

 In this course we will use NetBeans (Open Source by Sun).

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Java Development Tools (Continued)

A Simple Java Program

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 Line 1 defines a class. Every Java program must have at least one class. Each class has a name. By convention, class names start with an uppercase letter. In this example, the class name is Welcome.

 Line 2 defines the main method. In order to run a class, the

class must contain a method named main. The program is executed from the main method.

Output

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A Simple Java Program (Continued)

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 Line 3 is a comment that documents what the program is and

how it is constructed. Comments help programmers to communicate and understand the program.

 In Java, comments are preceded by two slashes (//) on a line,

called a line comment, or enclosed between /* and */ on one or several lines, called a block comment.

 A block groups the program’s components. In Java, each

block begins with an opening brace ({) and ends with a closing brace (}).

 Every class has a class block that groups the data and

methods of the class. Every method has a method block that groups the statements in the method.

 Blocks can be nested, meaning that one block can be placed within another.

Anatomy of a Java Program



Comments



Reserved words



Modifiers



Statements



Blocks



Classes



Methods



The

main

method

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Reserved Words



Reserved words or keywords are words that have a

specific meaning to the compiler and cannot be

used for other purposes in the program.



For example, when the compiler sees the word

class

, it understands that the word after class is the

name for the class.



Other reserved words in Listing 1.1 are

public

,

static

,

and

void

. Their use will be introduced later.

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Modifiers



Java uses certain reserved words called

modifiers

that specify the properties of the data, methods,

and classes and how they can be used.



Examples of modifiers are

public

and

static

. Other

modifiers are

private

,

final

,

abstract

, and

protected

.



A public datum, method, or class can be accessed

by other programs.



A private datum or method cannot be accessed by

other programs.



Modifiers are discussed later.

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Statements

 A statement represents an action or a sequence of actions.

 The statement

System.out.println("Welcome to Java!");

in the program in Listing 1.1 is a statement to display the greeting "Welcome to Java!" .

 Every statement in Java ends with a semicolon (;).

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Classes

 The class is the essential Java construct.  A class is a template or blueprint for objects.

 To program in Java, you must understand classes and be

able to write and use them.

 The mystery of the class will continue to be unveiled

throughout this course. For now, though, understand that a program is defined by using one or more classes.

Methods



What is System.out.println?



It is a method: a collection of statements that

performs a sequence of operations to display a

message on the console.



It can be used even without fully understanding the

details of how it works.



It is used by invoking a statement with a string

argument. The string argument is enclosed within

parentheses. In this case, the argument is

"Welcome to Java!“.



You can call the same println method with a different

argument to print a different message.

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main

Method



The

main

method provides the control of program

flow.



The Java interpreter executes the application by

invoking the

main

method.



The main method looks like this:

public static void main(String[] args) {

// Statements;

}

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Creating, Compiling, and Running Programs

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Welcome.java

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Compiling Java Source Code

 You can port a source program to any machine with

appropriate compilers. The source program must be

recompiled, however, because the object program can only run on a specific machine.

 Java was designed to run object programs on any platform.  With Java, you write the program once, and compile the

source program into a special type of object code, known as bytecode. The bytecode can then run on any computer with a Java Virtual Machine, as shown below.

 Java Virtual Machine is a software that interprets Java

bytecode.

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Creating, Compiling, and Running Java

from the Command Window



Set path to JDK bin directory

 Set Path=C:\Program Files\Java\jdk1.8.0_60\bin

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

On Microsoft Windows s

et the PATH variable as follows:

 Click Start, then Control Panel, then System.  Click Advanced, then Environment Variables.

 Add the location of the bin folder of the JDK installation

C:\Program Files\Java\jdk1.8.0_60\bin for the PATH variable in System Variables.

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Creating, Compiling, and Running Java

from the Command Window



Create a source file

that will contain the Java code.

You can use any text editor, such as Notepad, to

create and edit source files.



Compile the source file:



javac Welcome.java



Run

the bytecode:



java Welcome

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I. Create an IDE Project

To create an IDE project:

1. Launch the NetBeans IDE.

2. In the NetBeans IDE, choose File | New Project....

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Creating, Compiling, and Running Java

using the NetBeans IDE

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3. In the New Project wizard, expand the Java category and select Java Application as shown in the following figure:

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Creating, Compiling, and Running Java

using the NetBeans IDE (Continued)

4. In the Name and Location page of the wizard, do the following (as shown in the figure below):



In the Project

Name field,

type

Welcome

.



In the Create

Main Class

field, the name

welcome.Welcome

will appear.

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Creating, Compiling, and Running Java

using the NetBeans IDE (Continued)

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14/16 5. Click Finish.

The project is created and opened in the IDE. You should see the following components:

 The Projects window, which contains a tree view of the

components of the project, including source files, libraries that your code depends on, and so on.

 The Source Editor window with a file called

Welcome.java open.

 The Navigator window, which you can use to quickly

navigate between elements within the selected class.

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Creating, Compiling, and Running Java

using the NetBeans IDE (Continued)

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Creating, Compiling, and Running Java

using the NetBeans IDE (Continued)

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II. Add Code to the Generated Source File

 When you created this project, you left the Create Main

Class checkbox selected in the New Project wizard. The

IDE has therefore created a skeleton class for you. You can add the code for displaying the "Welcome to Java!" message to the skeleton code by replacing the line:

// TODO code application logic here with the line:

System.out.println("Welcome to Java!");

III. Save your changes by choosing File | Save.

IV. Compile the Source File into a .class File

 Choose Run | Build Project (Welcome) from the IDE's

main menu.

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Creating, Compiling, and Running Java

using the NetBeans IDE (Continued)

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Creating, Compiling, and Running Java

using the NetBeans IDE (Continued)

 The Output window opens and displays output similar to

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 If the build output concludes with the statement BUILD

SUCCESSFUL, congratulations! You have successfully

compiled your program!

 If the build output concludes with the statement BUILD

FAILED, you probably have a syntax error in your code. Errors are reported in the Output window as hyperlinked text. You double-click such a hyperlink to navigate to the source of an error. You can then fix the error and once again choose Run | Build Project.

 When you build the project, the bytecode file

Welcome.class is generated.

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Creating, Compiling, and Running Java

using the NetBeans IDE (Continued)

V. Run the Program

 From the IDE's menu bar, choose:

Run | Run Project (Welcome).

 The next figure shows what you should now see.

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