Introduction to Java Programming Language

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1
© University of Sulaimani, Faculty of Physical & Basic Education, Department of Computer Science 2014 / 2015

Objectives
To review computer basics, programs, and operating
systems
To explore the relationship between Java and the World
Wide Web
To distinguish the terms API, IDE, and JDK
To write a simple Java program
To display output on the console
To explain the basic syntax of a Java program
To create, compile, and run Java programs
(GUI) To display output using the JOptionPane output
dialog boxes
2
© University of Sulaimani, Faculty of Physical Basic Education, Department of Computer Science 2014 / 2015

What is a Computer?
A computer consists of a CPU, memory, hard disk, floppy disk,
monitor, printer, and communication devices.
CPU
e.g., Disk, CD,
and Tape
Input
Devices
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
Communication
Devices
e.g., Modem,
and NIC
Storage
Devices
Memory
Output
Devices
Bus
3

CPU
The central pprroocceessssiinngg uunniitt (CPU) is the brain of a computer. It
retrieves instructions from memory and executes them. The CPU
speed is measured in megahertz (MHz), with 1 megahertz equaling 1
million pulses per second. The speed of the CPU has been improved
continuously. If you buy a PC now, you can get an Intel Pentium 4
Processor at 3 gigahertz or more (1 gigahertz is 1000 megahertz).
CPU
e.g., Disk, CD,
and Tape
Input
Devices
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
Communication
Devices
e.g., Modem,
and NIC
Storage
Devices
Memory
Output
Devices
Bus
4

Memory
MMeemmoorryy is to store data and program instructions for CPU to
execute. A memory unit is an ordered sequence of bytes, each holds
eight bits. A program and its data must be brought to memory before
they can be executed.
CPU
e.g., Disk, CD,
and Tape
Input
Devices
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
Communication
Devices
e.g., Modem,
and NIC
Storage
Devices
Memory
Output
Devices
Bus
5

Storage Devices
Memory is volatile, because information is lost when the power is
off. Programs and data are permanently stored on storage devices
and are moved to memory when the computer actually uses them.
There are three main types of storage devices: Disk drives (hard
disks and floppy disks), CD drives (CD-R and CD-RW), and Tape
drives.
CPU
e.g., Disk, CD,
and Tape
Input
Devices
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
Communication
Devices
e.g., Modem,
and NIC
Storage
Devices
Memory
Output
Devices
Bus
6

Output Devices: Monitor
The monitor displays information (text and graphics). The resolution
and dot pitch determine the quality of the display.
CPU
e.g., Disk, CD,
and Tape
Input
Devices
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
Communication
Devices
e.g., Modem,
and NIC
Storage
Devices
Memory
Output
Devices
Bus
7

Communication Devices
A regular modem uses a phone line and can transfer data in a speed up to
56,000 bps (bits per second). A DSL (digital subscriber line) also uses a
phone line and can transfer data in a speed 20 times faster than a regular
modem. A cable modem uses the TV cable line maintained by the cable
company. A cable modem is as fast as a DSL. Network interface card
(NIC) is a device to connect a computer to a local area network (LAN).
The LAN is commonly used in business, universities, and government
organizations. A typical type of NIC, called 10BaseT, can transfer data at
10 mbps (million bits per second).
CPU
e.g., Disk, CD,
and Tape
Input
Devices
e.g., Keyboard,
Mouse
e.g., Monitor,
Printer
Communication
Devices
e.g., Modem,
and NIC
Storage
Devices
Memory
Output
Devices
Bus
8

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.
9

Programming Languages
Machine Language Assembly Language High-Level Language
MMaacchhiinnee llaanngguuaaggee 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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AAsssseemmbbllyy llaanngguuaaggeess 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
Assembly Source File
…
ADDF3 R1, R2, R3
…
Assembler
Machine Code File
…
1101101010011010
…
11

The hhiigghh--lleevveell llaanngguuaaggeess 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;
12

Popular High-Level Languages
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 (whose developer designed B first)
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# (a Java-like language developed by Microsoft)
Java (We use it during the course)
13

Compiling Source Code
A program written in a high-level language is called a
ssoouurrccee pprrooggrraamm. Since a computer cannot understand a
source program. Program called a ccoommppiilleerr is used to
translate the source program into a machine language
program called an oobbjjeecctt pprrooggrraamm.. The object program is
often then linked with other supporting library code before
the object can be executed on the machine.
Source File Compiler Machine-language
File Linker Executable File
Library Code
14

Why Java?
The answer is that Java 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 is a general purpose programming language.
Java is the Internet programming language.
15

Java, Web, and Beyond
Java can be used to develop Web
applications.
Java Applets
Java Web Applications
Java can also be used to develop applications
for hand-held devices such as Palm and cell
phones
16

Examples of Java’s Versatility (Applets)
17

PDA and Cell Phone
PDA
Cell Phone
18

Java’s History
James Gosling and Sun Microsystems
Oak
Java, May 20, 1995, Sun World
HotJava
– The first Java-enabled Web browser
Early History Website:
http://java.sun.com/features/1998/05/birthday.html
19

Characteristics of Java (2math)
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust ( full power and strong)
Java Is Secure
Java Is Architecture-Neutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
20

Characteristics of Java
Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Java is partially modeled on C++, but greatly
simplified and improved. Some people refer to
Java as C++-- because it is like C++ but
with more functionality and fewer negative
aspects.
21

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Java is inherently object-oriented.
Although many object-oriented languages
began strictly as procedural languages,
Java was designed from the start to be
object-oriented. Object-oriented
programming (OOP) is a popular
programming approach that is replacing
traditional procedural programming
techniques.
One of the central issues in software
development is how to reuse code. Object-oriented
programming provides great
flexibility, modularity, clarity, and
reusability through encapsulation,
inheritance, and polymorphism.
22

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Distributed computing involves several
computers working together on a network.
Java is designed to make distributed
computing easy. Since networking
capability is inherently integrated into
Java, writing network programs is like
sending and receiving data to and from a
file.
23

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
You need an interpreter to run Java
programs. The programs are compiled into
the Java Virtual Machine code called
bytecode. The bytecode is machine-independent
and can run on any machine
that has a Java interpreter, which is part of
the Java Virtual Machine (JVM).
24

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust ( strong )
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Java compilers can detect many problems
that would first show up at execution time
in other languages.
Java has eliminated certain types of error-prone
programming constructs found in
other languages.
Java has a runtime exception-handling
feature to provide programming support
for robustness.
25

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Java implements several security
mechanisms to protect your system against
harm caused by stray programs.
26

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Write once, run anywhere
With a Java Virtual Machine (JVM),
you can write one program that will
run on any platform.
27

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Because Java is architecture neutral,
Java programs are portable. They can
be run on any platform without being
recompiled.
28

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Java’s performance Because Java is
architecture neutral, Java programs
are portable. They can be run on any
platform without being recompiled.
29

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Multithread programming is smoothly
integrated in Java, whereas in other
languages you have to call procedures
specific to the operating system to enable
multithreading.
30

Java Is Simple
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is Portable
Java's Performance
Java Is Dynamic
Java was designed to adapt to an evolving
environment. New code can be loaded on the
fly without recompilation. There is no need for
developers to create, and for users to install,
major new software versions. New features can
be incorporated transparently as needed.
31

JDK: Java Development kit
A package of software distributed by Sun
Microsystems for Java developers that
implements the basic set of tools needed to
write, test and debug Java applications and
applets.
32

JDK Versions
JDK 1.02 (1995)
JDK 1.1 (1996)
JDK 1.2 (1998)
JDK 1.3 (2000)
JDK 1.4 (2002)
JDK 1.5 (2004) a. k. a. JDK 5 or Java 5
JDK 1.6 (2006) a. k. a. JDK 6 or Java 6
JDK 1.7 (possibly 2010) a. k. a. JDK 7 or Java 7
33

JDK Editions
Java Standard Edition (J2SE)
– J2SE can be used to develop client-side standalone
applications or applets.
Java Enterprise Edition (J2EE)
– J2EE can be used to develop server-side applications
such as Java servlets and Java ServerPages.
Java Micro Edition (J2ME).
– J2ME can be used to develop applications for mobile
devices such as cell phones.
34

Popular Java IDEs
NetBeans Open Source by Sun
Eclipse Open Source by IBM
35

A Simple Java Program
Listing 1.1
//This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println(Welcome to Java!);
}
}
RReessuulltt
36

Creating and Editing Using NotePad
To use NotePad, type
notepad Welcome.java
from the DOS prompt.
37

Creating and Editing Using WordPad
To use WordPad, type
write Welcome.java
from the DOS prompt.
38

//This program prints Welcome to Java!
}
}
Trace a Program Execution
Enter main method
39

}
}
Execute statement
40

}
}
print a message to the
console
41

Compiling and Running Java
from TextPad
See practical lecture on the Website for details
42

Compiling and Running Java
from JBuilder
43

Compiling and Running
Java from NetBeans
44

Anatomy of a Java Program
Comments
Reserved words
Modifiers
Statements
Blocks
Classes
Methods
The main method
45

Comments
Three types of comments in Java.
Line comment: A line comment is preceded by two
slashes (//) in a line.
Paragraph comment: A paragraph comment is enclosed
between /* and */ in one or multiple lines.
javadoc comment: javadoc comments begin with /**
and end with */. They are used for documenting
classes, data, and methods. They can be extracted
into an HTML file using JDK's javadoc command.
46

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 in the book.
47

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.
48

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 (;).
49

Blocks
A pair of braces in a program forms a block that groups
components of a program.
public class Test {
}
}
Class block
Method block
50

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 book. For now, though,
understand that a program is defined by using one or
more classes.
51

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.
52

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:
// Statements;
}
53

Displaying Text in a Message
Dialog Box
you can use the showMessageDialog method in the
JOptionPane class. JOptionPane is one of the many
predefined classes in the Java system, which can be
reused rather than “reinventing the wheel.”
54

The showMessageDialog Method
JOptionPane.showMessageDialog(null,
Welcome to Java!,
Display Message,
JOptionPane.INFORMATION_MESSAGE);
55

Two Ways to Invoke the Method
There are several ways to use the showMessageDialog
method. For the time being, all you need to know are
two ways to invoke it.
One is to use a statement as shown in the example:
JOptionPane.showMessageDialog(null, x,
y, JOptionPane.INFORMATION_MESSAGE);
where x is a string for the text to be displayed, and y is
a string for the title of the message dialog box.
The other is to use a statement like this:
JOptionPane.showMessageDialog(null, x);
where x is a string for the text to be displayed.
56

Introduction to Java Programming Language

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