Chapter-introduction about java programming

Unit-1
Introduction to Java and Elementary
Programming
Dr. Rajesh Patel
Department of Computer Engineering, SPCE

Machine Language
• A computer’s native language.
• Differs among different types of computers, is its
machine language—a set of built-in primitive
instructions.
• These instructions are in the form of binary code.
• To give a computer an instruction in its native
language, have to enter the instruction as binary
code.

Contd..
• For example, to add two numbers, you might
have to write an instruction in binary code,
like this:
• 1101101010011010

Assembly Language
• Programming in machine language is a tedious
process.
• Programs written in machine language are very
difficult to read and modify.
• Assembly language was created in the early days of
computing as an alternative to machine languages.
• Assembly language uses a short descriptive word,
known as a mnemonic, to represent each of the
machine-language instructions.

High-Level Language
• In the 1950s, a new generation of programming languages
known as high-level languages emerged.
• They are platform independent.
• User can write program in a high-level language and run it in
different types of machines.
• The instructions in a high-level programming language are
called statements.
• for example, is a high-level language statement that
computes the area of a circle with a radius of 5:
area = 5 * 5 * 3.14159;

High level languages
• A program written in a high-level language is
called a source program or source code.
• Because a computer cannot execute a source
program, a source program must be translated
into machine code for execution.
• The translation can be done using another
programming tool called an interpreter or a
compiler

Interpreter & Compiler
• An interpreter reads one statement from the
source code, translates it to the machine code
or virtual machine code, and then executes it
right away.
• Statements from the source code may be
translated into several machine instructions

Interpreter & Compiler
FIGURE (a) An interpreter translates and executes a program one statement at a
time. (b) A compiler translates the entire source program into a machine-
language file for execution.
(a)
(b)

Java, the World Wide Web, and
Beyond
• Java is a powerful and versatile programming language for
developing software running on mobile devices, desktop
computers, and servers.
• Java was developed by a team led by James Gosling at Sun
Microsystems.
• Sun Microsystems was purchased by Oracle in 2010.
• Originally called Oak, Java was designed in 1991 for use in
embedded chips in consumer electronic appliances.
• In 1995, renamed Java, it was redesigned for developing
Web applications.

Contd..
• Java is a full-featured, general-purpose programming
language that can be used to develop robust mission-
critical applications.
• Today, it is employed not only for Web programming
but also for developing standalone applications
across platforms on servers, desktop computers, and
mobile devices.

Contd..
• It was used to develop the code to communicate
with and control the robotic rover on Mars
• Distributed applications accessed by customers
and partners across the Internet
• For every new project being developed today,
companies are asking how they can use Java to
make their work easier

Java Applets
• Java initially became attractive because 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.
• Applets make the Web responsive, interactive,
and fun to use.

HTML
• Applets are embedded in an HTML file.
• HTML (Hypertext Markup Language) is a
simple scripting language for laying out
documents, linking documents on the
Internet, and bringing images, sound, and
video alive on the Web.
`

Contd..
• Java is now very popular for developing
applications on Web servers.
• These applications process data, perform
computations, and generate dynamic Web
pages.

Java API, JDK, IDE
• Java syntax is defined in the Java language
specification, and the Java library is defined in
the Java API.
• The JDK is the software for developing and
running Java programs.
• An IDE is an integrated development
environment for rapidly developing programs

Java Computing Platform
 Java Standard Edition (Java SE) to develop client-side
applications. The applications can run standalone or as
applets running from a Web browser.
 Java Enterprise Edition (Java EE) to develop server-side
applications, such as Java servlets, JavaServer Pages
(JSP), and JavaServer Faces (JSF).
 Java Micro Edition (Java ME) to develop applications
for mobile devices, such as cell phones.

JDK & Java Development Tools
• The 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, - Java development tool (e.g.,
NetBeans, Eclipse, and TextPad)—software that
provides an integrated development environment (IDE)
for developing Java programs quickly.
• Editing, compiling, building, debugging, and online
help are integrated in one graphical user interface.

Contd..
• Reserved words, or keywords, have a specific meaning to the
compiler and cannot be used for other purposes in the
program.
C

Appropriate Comments and Comment Styles
• Line comments (beginning with //)
• Block comments (beginning with /*),
• Java supports comments of a special type,
referred to as javadoc comments.
• javadoc comments begin with /** and end with
*/.
• They can be extracted into an HTML file using the
JDK’s javadoc command.

Programming Errors
• Programming errors can be categorized into
three types: syntax errors, runtime errors, and
logic errors.
• Syntax errors result from errors in code
construction, such as mistyping a keyword,
omitting some
• Necessary punctuation, or using an opening
brace without a corresponding closing brace

Runtime error
Runtime errors are errors that cause a program to terminate
abnormally. They occur while a program is running if the
environment detects an operation that is impossible to carry
out. Input mistakes typically cause runtime errors.

Logic Errors
• Logic errors occur when a program does not perform
the way it was intended to.
• Errors of this kind occur for many different reasons.

Reading Input from the Console
• Reading input from the console enables the
program to accept input from the user.
• Java uses System.out to refer to the standard
output device.
• System.in to the standard input device.

Read Input
• Console input is not directly supported in Java.
• Scanner class to create an object to read input
from System.in, as follows:
Scanner input = new Scanner(System.in);
double radius = input.nextDouble();
• The Scanner class is in the java.util package
• import java.util.Scanner;

Identifier
• Identifiers are the names that identify the
elements such as classes, methods, and
variables in a program.
Example:
• ComputeAverage, main, input, number1,
number2.

Rules
• An identifier is a sequence of characters that consists of
letters, digits, underscores(_), and dollar signs ($).
• An identifier must start with a letter, an underscore (_),
or a dollar sign ($). It cannot start with a digit.
• An identifier cannot be a reserved word.
• An identifier cannot be true, false, or null.
• An identifier can be of any length.

Variables
• Variables are used to represent values that
may be changed in the program.
int count;
double radius;
double interestRate;

Contd..
int i, j, k;
int count = 1;
This is equivalent to the next two statements:
int count;
count = 1;
int i = 1, j = 2;
C

Named Constants
• A named constant is an identifier that
represents a permanent value.
• The value of a variable may change during
the execution of a program, but a named
constant, or simply constant, represents
permanent data that never changes.

Contd..
final datatype CONSTANTNAME = value;
• A constant must be declared and initialized in
the same statement.
The word final is a Java keyword for declaring
a constant.
final double PI = 3.14159;
Cont

Naming Conventions
• Sticking with the Java naming conventions
makes your programs easy to read and avoids
errors.

Numeric Literals
• A literal is a constant value that appears
directly in a program.
• For example, 34 and 0.305 are literals in the
following statements:
• int numberOfYears = 34;
• double weight = 0.305;

Integer Literals
• An integer literal can be assigned to an integer
variable as long as it can fit into the variable.
• A compile error will occur if the literal is too large
for the variable to hold.
The statement byte b = 128,
• for example, will cause a compile error, because
128 cannot be stored in a variable of the byte
type.

Contd..
• An integer literal is assumed to be of the int
type, whose value is between
-231 (-2147483648) and 231 - 1 (2147483647).
C

Floating-Point Literals
• Floating-point literals are written with a
decimal point.
• By default, a floating-point literal is treated as
a double type value.
• For example, 5.0 is considered a double value,
not a float value.

Contd..
• For example, you can use 100.2f or
• 100.2F for a float number,
• 100.2d or 100.2D for a double number.
C

Double & Float
• The double type values are more accurate than
the float type values.
• System.out.println("1.0 / 3.0 is " + 1.0 / 3.0);
• displays 1.0 / 3.0 is 0.3333333333333333
• System.out.println("1.0F / 3.0F is " + 1.0F / 3.0F);
• 1.0F / 3.0F is 0.33333334

Evaluating Expressions and Operator
Precedence
• Java expressions are evaluated in the same
way as arithmetic expressions.

Operator Precedence Rule
 Operators within pairs of parentheses are evaluated first.
Parentheses can be nested, in which case the expression in
the inner parentheses is evaluated first. When more than
one operator is used in an expression, the following operator
precedence rule is used to determine the order of evaluation.
 Multiplication, division, and remainder operators are
applied first. If an expression contains several multiplication,
division, and remainder operators, they are applied from left
to right.
 Addition and subtraction operators are applied last. If an
expression contains several addition and subtraction
operators, they are applied from left to right.

Increment and Decrement Operators
• The increment operator (++) and decrement
operator (– –) are for incrementing and
decrementing a variable by 1.
int i = 3, j = 3;
i++; // i becomes 4
j——; // j becomes 2

Contd..
• int i = 3, j = 3;
• ++i; // i becomes 4
• ——j; // j becomes 2
• double x = 1.0;
• double y = 5.0;
• double z = x–– + (++y);
• After all three lines are executed, y becomes 6.0,
z becomes 7.0, and x becomes 0.0.
Cn

Numeric Type Conversion
• Floating-point numbers can be converted into
integers using explicit casting.
System.out.println((int)1.7);
System.out.println((double)1 / 2);
Output : 0.5

Contd..
• System.out.println(1 / 2);
Output : 0
C

Chapter-introduction about java programming

More Related Content

Similar to Chapter-introduction about java programming (20)

Recently uploaded (20)

Chapter-introduction about java programming

Editor's Notes