What is a Computer?public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
animation
print a message to the
console
Anatomy of a Java Program
oComments
oReserved words
oModifiers
oStatements
oBlocks
oClasses
oMethods
oThe main method
18
Comments
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. 19
Three types of comments in Java. 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. 20
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. 21
Statements
o A statement represents an action or a sequence of
actions. o 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!"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;
Popular High-Level Languages
oCOBOL (COmmon Business Oriented Language)
oFORTRAN (FORmula TRANslation)
oBASIC (Beginner All-purpose Symbolic Instructional Code)
oPascal (named for Blaise Pascal)
oAda (named for Ada Lovelace)
oC (whose developer designed B first)
oVisual Basic (Basic-like visual language developed by Microsoft)
oDelphi (Pascal-like visual language developed by Borland)
oC++ (an object-oriented language, based on C)
oC# (a Java-like language developed by Microsoft)
oJava (We use it in the book)
9
Operating Systems
Operating systems are software systems that make using
computers more convenient for users, application developers and
system administrators.01001010
01100001
01110110
01100001
00000011
Memory content
Memory address
Encoding for character 'J'
Encoding for character 'a'
Encoding for character 'v'
Encoding for character 'a'
Encoding for number 3
Storage 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
4
Memory is volatile, because information is lost when the power is off.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
How Data is Stored?The main method looks like this:
public static void main(String[] args) {
// Statements;
}
27
The showMessageDialog Method
JOptionPane.showMessageDialog(null,
"Welcome to Java!",
"Display Message",
JOptionPane.INFORMATION_MESSAGE);10
Linux Windows Mac OS Android BlackBerry
OS
Apple's iOS
x86 Architecture
CPU Memory
NIC Card Hard Disk
Why Java?11
The answer is that Java enables users to develop and
deploy applications on the Internet for servers, desktop
computers, and small hand-held devices.public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Enter main method
Trace a Program Execution
16
//This program prints Welcome to Java! public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Execute statement
animation
Trace a Program Execution
17
//This program prints Welcome to Java!2
A computer consists of a CPU, memory, hard disk, floppy disk, monitor, printer, and
communication devices.For example, to add two numbers, you might write an
instruction in assembly code like this:
ADDF3 R1, R2, R3
...
ADDF3 R1, R2, R3
...
Assembly Source File
Assembler ...
1101101010011010
...
Machine Code File
Programming Languages
Machine Language Assembly Language High-Level Language
8
The high-level languages are English-like and easy to learn
and program.Data of various kinds, such as numbers,
characters, and strings, are encoded as a
series of bits (zeros and ones).Computers
use zeros and ones because digital devices
have two stable states, which are referred
to as zero and one by convention.The
programmers need not to be concerned
about the encoding and decoding of data,
which is performed automatically by the
system based on the encoding scheme.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.For example, to add two numbers, you
might write an instruction in binary like this:
1101101010011010
Programming Languages
Machine Language Assembly Language High-Level Language
7
Assembly languages were developed to make programming
easy.Operating systems provide services that
allow each application to execute safely, efficiently and concurrently
(i.e., in parallel) with other applications.The software that contains
the core components of the operating system is called the kernel.Popular Java IDEs
oNetBeans Open Source by Sun
oEclipse Open Source by IBM
12
A Simple Java Program
13
Listing 1.1
Compiling Java Source Code
You can port a source program to any machine with appropriate
compilers.Programs and data
are permanently stored on storage devices and are moved to memory when the
computer actually uses them.Java Virtual Machine is a software that interprets Java
bytecode.Programs are written using programming languages.3
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