introduction to python programming language.ppt

Liang, Introduction to Java Programming, Eleventh Edition, (c) 2018 Pearson Education, Ltd.
All rights reserved.
1
Chapter 1
Introduction to Computers,
Programs, Object Oriented
Programming and Java

2
How Data is Stored?
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. The
encoding scheme varies. For example,
character ‘J’ is represented by 01001010 in
one byte. A small number such as three can
be stored in a single byte. If computer needs
to store a large number that cannot fit into a
single byte, it uses a number of adjacent
bytes. No two data can share or split a same
byte. A byte is the minimum storage unit.
.
.
.
2000
2001
2002
2003
2004
.
.
.
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

3
Programming Languages
Machine Language Assembly Language High-Level Language
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

4
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

5
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;

6
Popular High-Level Languages
Language Description
Ada
BASIC
C
C++
C#
COBOL
FORTRAN
Java
Pascal
Python
Visual
Basic
Named for Ada Lovelace, who worked on mechanical general-purpose computers. The Ada
language was developed for the Department of Defense and is used mainly in defense projects.
Beginner’s All-purpose Symbolic Instruction Code. It was designed to be learned and used easily
by beginners.
Developed at Bell Laboratories. C combines the power of an assembly language with the ease of
use and portability of a high-level language.
C++ is an object-oriented language, based on C.
Pronounced “C Sharp.” It is a hybrid of Java and C++ and was developed by Microsoft.
COmmon Business Oriented Language. Used for business applications.
FORmula TRANslation. Popular for scientific and mathematical applications.
Developed by Sun Microsystems, now part of Oracle. It is widely used for developing platform-
independent Internet applications.
Named for Blaise Pascal, who pioneered calculating machines in the seventeenth century. It is a
simple, structured, general-purpose language primarily for teaching programming.
A simple general-purpose scripting language good for writing short programs.
Visual Basic was developed by Microsoft and it enables the programmers to rapidly develop
graphical user interfaces.

7
Compiling Source Code in C
 A program written in a high-level language is
called a source program or source code. Because
a computer cannot understand a source program,
a source program must be translated into machine
code for execution.
 To run the source code of a C program, we need a
C compiler. The C compiler generates assembly
code (.s file) first. The assembler produces the
machine code (.obj file). Finally, the linker
produces the executable machine code (.exe file)

8
Compiling/Interpreting Source Code in Java
 To run the source code of a Java program, we
need a Java compiler and a Java interpreter. The
Java compiler compiles source files (.java) to
generate bytecode (.class) files. We can use the
javac command provided by Sun in the terminal
window.
 Note that a statement from the source code may
be translated into several instructions in .class
file.

9
Interpreting Source Code
 Although the bytecode is similar to machine level codes,
it is not directly executable.
 The Java Virtual Machine (JVM) is used to load .class
files into the memory and interpret the code. The
Execution Engine or Just-In-Time compiler (JIT)
(executable name: java) reads one statement from the
bytecode in memory, translates it to the machine code of
the target platform, and then executes it right away.
 JVM helps to avoid the need to recompile the source
code for every specific platform.

10
Major Differences Between Java and C
 No goto statement in Java
 No pointers in Java
 No unsigned data type
 No call-by-reference
 16 bit characters
 OOP rather than procedural
 long integers use 8 bytes
 Additional primitive types such as “byte”

11
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 a general purpose programming language.
Java is an internet programming language.

12
Java, Web, and Beyond
 Java can be used to develop standalone
applications.
 Java can be used to develop applications
running from a browser.
 Java can also be used to develop applications
for hand-held devices.
 Java can be used to develop applications for
Web servers.

13
Characteristics of Java
 Java Is Simple
 Java Is Object-Oriented
 Java Is Distributed
 Java Is Interpreted
 Java Is Robust
 Java Is Secure
 Java Is Architecture-Neutral
 Java Is Portable
 Java's Performance
 Java Is Multithreaded
 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.
Companion
Website

14
 Java Is Simple
 Java Is Robust
 Java Is Secure
 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.
Companion
Website

15
 Java Is Simple
 Java Is Robust
 Java Is Secure
 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.
Companion
Website

16
 Java Is Simple
 Java Is Robust
 Java Is Secure
 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).
Companion
Website

17
 Java Is Simple
 Java Is Robust
 Java Is Secure
 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.
Companion
Website

18
 Java Is Simple
 Java Is Robust
 Java Is Secure
 Java Is Dynamic
Java implements several security
mechanisms to protect your system against
harm caused by stray programs.
Companion
Website

19
 Java Is Simple
 Java Is Robust
 Java Is Secure
 Java Is Dynamic
Write once, run anywhere
With a Java Virtual Machine (JVM),
you can write one program that will
run on any platform.
Companion
Website

20
 Java Is Simple
 Java Is Robust
 Java Is Secure
 Java Is Dynamic
Because Java is architecture neutral,
Java programs are portable. They can
be run on any platform without being
recompiled.
Companion
Website

21
 Java Is Simple
 Java Is Robust
 Java Is Secure
 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.
Companion
Website

22
 Java Is Simple
 Java Is Robust
 Java Is Secure
 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.
Companion
Website

23
Application Interface
 The application program interface (API), also known
as library, contains predefined classes and interfaces
for developing Java programs
 The Java Development Toolkit (JDK) consists of a set
of separate programs, each invoked from a command
line, for developing and testing Java programs.
Instead of using the JDK, you can use a Java
development tool (e.g., NetBeans, Eclipse, and
TextPad)—software that provides an integrated
development environment (IDE) for developing Java
programs quickly

24
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

25
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, Java ServerPages, and Java
ServerFaces.
 Java Micro Edition (J2ME).
– J2ME can be used to develop applications for mobile
devices such as cell phones.
This book uses J2SE to introduce Java programming.

26
Popular Java IDEs
 NetBeans
 Eclipse

27
A Simple Java Program
 Every Java program must have at least one class. Each class
has a name. By convention, class names start with an
uppercase letter.
 In a program, multiple classes may cooperate with each other.
 Each program needs an entry point to start execution.
 The program is executed from the main method that is defined
in one of the classes. A class may contain several methods. The
main method is the entry point where the program begins
execution.

28
Creating, Compiling, and
Running Programs

29
Compiling Java Source Code
 The Java language is a high-level language, but Java bytecode is a
low-level language. The bytecode is similar to machine instructions
but is architecture neutral and can run on any platform that has a
Java Virtual Machine (JVM).
 The virtual machine is a program that interprets Java bytecode. This
is one of Java’s primary advantages: Java bytecode can run on a
variety of hardware platforms and operating systems.
 Java source code is compiled into Java bytecode (.class file) and
Java bytecode is interpreted by the JVM. Your Java code may use
the code in the Java library. To execute a Java program is to run the
program’s bytecode.

30
 You can execute the bytecode on any platform with a JVM, which is
an interpreter and resides in RAM. It translates the individual
instructions in the bytecode into the target machine (i.e. the machine
on which it is working at) language code one at a time rather than
the whole program as a single unit.
 Each step is executed immediately after it is translated.
 The bytecode can then run on any computer with a Java Virtual
Machine, as shown below. In fact, Java Virtual Machine is a
software that interprets Java bytecode.

31

32
Procedural versus Object-Oriented
Programming
 The procedural programming aims at solving problems using a
collection of variables and functions. This approach is not
manageable as the size of the code gets large.
 Object-oriented programming (OOP) is an alternative approach
where variables and functions are combined to form classes.
 The procedural paradigm focuses on designing methods. The
object-oriented paradigm couples data and methods together
into objects. Software design using the object-oriented
paradigm focuses on objects and operations on objects.
 Classes provide more flexibility and modularity for building
reusable software.

33

34
Procedural versus Object-Oriented
Programming
 In procedural programming, data and operations on the data are
separate, and this methodology requires passing data to methods.
 Object-oriented programming places data and the operations that
pertain to them in an object. This approach solves many of the
problems inherent in procedural programming. The object-
oriented programming approach organizes programs in a way
that mirrors the real world, in which all objects are associated
with both attributes and activities.
 Using objects improves software reusability and makes
programs easier to develop and easier to maintain. A Java
program can be viewed as a collection of cooperating objects.

35
Object-Oriented Programming Paradigm
 There are many different types of objects like trees, cars,
animals etc. around us
 These objects have different characteristics even if they belong
to the same type. For instance, different animals may have
different numbers of legs, height, size, color etc. Similarly,
different cars may have different sizes, colors, brand names etc.
 In object oriented programming, objects of the same type are
said to belong to the same class. In technical terms, a class is a
blueprint or template or structure that can be used to create
objects.

36

37
Object-Oriented Programming Paradigm
 All objects have two basic characteristics:
– Properties OR states
– Behavior
 Example:
– Each car has a state or a set of properties such as model, color, year, price
etc. (i.e. what each object has)
– Each car has a set of behaviors such as start, move, stop, turn, accelerate,
park etc. (i.e. what each object does)
 Conceptually, software objects are similar to the real world ones
 A software object has a set of properties represented using data
fields/variables. The behaviors of the objects are represented in
terms of methods.
 In OOP, objects are instances of a predefined class.

38

39
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
Trace a Program Execution
Enter main method

40
}
}
Execute statement

41
}
}
print a message to the
console

42
Anatomy of a Java Program
 Class name
 Main method
 Statements
 Statement terminator
 Reserved words
 Comments
 Blocks

43
}
}
Class Name
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.

44
}
}
Main Method
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.

45
}
}
Statement
A statement represents an action or a sequence of actions.
The statement System.out.println("Welcome to Java!") in
the program below is a statement to display the greeting
"Welcome to Java!”.

46
}
}
Statement Terminator
Every statement in Java ends with a semicolon (;).

47
}
}
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.

48
Blocks
A pair of braces in a program forms a block that groups
components of a program.
public class Test {
}
}
Class block
Method block

49
Special Symbols
Character Name Description
{}
()
[]
//
" "
;
Opening and closing
braces
Opening and closing
parentheses
Opening and closing
brackets
Double slashes
Opening and closing
quotation marks
Semicolon
Denotes a block to enclose statements.
Used with methods.
Denotes an array.
Precedes a comment line.
Enclosing a string (i.e., sequence of characters).
Marks the end of a statement.

50
}
}
{ … }

51
}
}
( … )

52
}
}
;

53
}
}
// …

54
}
}
" … "

55
Programming Style and
Documentation
 Appropriate Comments
 Naming Conventions
 Proper Indentation and Spacing Lines
 Block Styles

56
Appropriate Comments
 Include a summary at the beginning of the program to
explain what the program does, its key features, its
supporting data structures, and any unique techniques it
uses.
 In addition to line comments (beginning with //) and
block comments (beginning with /*), Java supports
comments of a special type, referred to as javadoc
comment (begin with /** and end with */). They can be
extracted into an HTML file using the JDK’s javadoc
command. Use javadoc comments (/** ... */) for
commenting on an entire class or an entire method.

57
Naming Conventions
 Choose meaningful and descriptive names.
 Class names:
– Capitalize the first letter of each word in the
name. For example, the class name
ComputeExpression.

58
Proper Indentation and Spacing
 A consistent indentation style makes
programs clear and easy to read, debug, and
maintain. Indentation is used to illustrate the
structural relationships between a program’s
components or statements.
 Spacing
– Use blank line to separate segments of the code.

59
Block Styles
 There are two popular styles, next-line style and end-of-line style, as shown
below.
public class Test
{
public static void main(String[] args)
{
System.out.println("Block Styles");
}
}
public class Test {
System.out.println("Block Styles");
}
}
End-of-line
style
Next-line
style

60
Programming Errors
 Syntax Errors
– Detected by the compiler
 Runtime Errors
– Causes the program to abort
 Logic Errors
– Produces incorrect result

61
Syntax Errors
public class ShowSyntaxErrors {
public static main(String[] args) {
System.out.println("Welcome to Java);
}
}

62
Runtime Errors
public class ShowRuntimeErrors {
System.out.println(1 / 0);
}
}

63
Logic Errors
public class ShowLogicErrors {
System.out.println("Celsius 35 is Fahrenheit degree ");
System.out.println((9 / 5) * 35 + 32);
}
}

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