L2 datatypes and variables

Programming in Java
Lecture 2: Java Basics: Keywords,
Constants, Variables and Data Types

Contents
• Introduction
• Object Oriented Programming
• Identifiers
• Keywords
• Primitive Data Types
• Constants
• Variables

Introduction
• Java is an Object Oriented Programming language.
• Its main features are:
• Platform Independence
• Security
• What is the difference between Platform Independence
and Portability?

Object Oriented Programming
• Object-oriented programming is a method of implementation
in which programs are organized as cooperative collections of
objects, each of which represents an instance of some class,
and whose classes are all members of one or more hierarchy of
classes united via inheritance relationships.
Basic Concepts:
• Object
• Classification
• Data Encapsulation
• Inheritance
• Polymorphism

• Object: An object is a discrete(distinct) entity that has well-
defined attributes and behavior.
• Classification: Objects with common attributes, behavior and
relationships with other objects are grouped into a logical unit
called classes. This process is called Classification.
• Data Encapsulation: Encapsulation is the mechanism that
binds together code and the data it manipulates, and keeps both
safe from outside interference and misuse.
• In a class, One can not use the methods and data without any
object of that class.

• Inheritance: Inheritance is the process by which one object
acquires the properties of another object.
• Polymorphism: Polymorphism refers to a programming
language's ability to process objects differently depending on
their data type or class.
•A method or function behaves differently in different
conditions.
•Example: method overloading, overriding
• 7 + 5
• 10.38 + 1.62

Data Types, Variables and Constants
• Java is a strongly typed language.
• It means:
• Every variable has a type
• Every expression has a type, and every type is strictly
defined
•All assignments, whether explicit or via parameter
passing in method calls, are checked for type
compatibility.
• Any type mismatches are errors.

Identifiers
• A name in a program is called an identifier.
• Identifiers can be used to denote classes, methods,
variables, and labels.
• An identifier may be any descriptive sequence of uppercase
and lowercase letters, numbers, or the underscore and dollar-
sign characters.
• Example: number, Number, sum_$, bingo, $$_100
Note: Identifiers must not begin with a number.

Keywords
• Keywords are reserved identifiers that are predefined in the
language.
• Cannot be used as names for a variable, class, or method.
• All the keywords are in lowercase.
• There are 50 keywords currently defined in the Java language.
•The keywords const and goto are reserved but not used.
• true, false, and null are also reserved.

Java Keywords
abstract char else goto long return throw
assert class enum if native short throws
boolean const extends implements new static this
break continue final import package strictfp transient
byte default finally instanceof private super void
case do float int protected switch try
catch double for interface public synchronized while and
volatile

Primitive Data Types
• Classification of primitive data types
• Java defines eight primitive types of data:
• byte
• short
• int
• long
• char
• float
• double
• boolean

Primitive Data Types
Boolean Type Numeric Type
Integral Types Floating
point Types
Character Type Integer Types
boolean char byte short int long float double

These primitive types can be put in four groups:
• Integers: includes byte, short, int, and long, which are for
whole-valued signed numbers.
• Floating-point numbers: includes float and double, which
represent numbers with fractional precision.
• Characters: includes char, which represents symbols in a
character set, like letters and numbers.
• Boolean: includes boolean, which is a special type for
representing true/false values.

Integers
• Java defines four integer types: byte, short, int, and
long.
•All of these are signed, positive and negative
values.
•Java does not support unsigned, positive-only
integers.

Type Width
(bits)
Range
Byte 8 –128 to 127
Short 16 –32,768 to 32,767
Int 32 –2,147,483,648 to 2,147,483,647
Long 64 –9,223,372,036,854,775,808 to
9,223,372,036,854,775,807

Floating-Points
• Floating-point numbers, also known as real numbers,
are used when evaluating expressions that require
fractional precision.
• There are two kinds of floating-point types, float and
double, which represent single- and double-precision
numbers, respectively.
•By default floating point constants are double type in
java.

Type Width (bits) Approximate Range
Float 32 1.4e–045 to 3.4e+038
Double 64 4.9e–324 to 1.8e+308

Float
• Float specifies a single-precision value that uses 32 bits
of storage.
• Single precision is faster on some processors and takes
half as much space as double precision.
• Variables of type float are useful when we need a
fractional component with small precision.
• float a = 12.50f;

Double
• Double provides high precision, and uses 64 bits to store
a value.
• Double precision is actually faster than single precision
on some modern processors.
• All transcendental math functions, such as sin( ), cos( ),
and sqrt( ), return double values.
• Double is useful when we need to maintain accuracy
over many iterative calculations.

Characters
• Data type used to store characters is char.
• Unlike C/C++ (8 bits), Java char is a 16-bit type.
• The range of a char is 0 to 65,536.
• There are no negative chars.
• char variables behave like integers (as shown in the
example).

class CharTest{
public static void main(String args[])
{
char c1;
c1 = ‘A’;
System.out.println("c1 is currently " + c1);
c1++;
System.out.println("c1 is now " + c1);
}
}
Output: c1 is currently A
c1 is now B

Boolean
• Boolean can have only one of two possible values, true
or false.
•This is the return type of all relational operators.
• e.g. a < b (either true or false)
•Boolean is also the type required by the conditional
expressions that govern the control statements such as if
and for.
• e.g. if ( x == 5)

Constants
• The values of the constant can't be changed once its
declared.
•Constants are declared using the final keyword.
•Even though Java does not have a constant type, we can
achieve the same effect by declaring and initializing variables
that are static, public, and final.
•Example:
final int NUMBER_OF_HOURS_IN_A_DAY = 24;

Variables
• The variable is the basic unit of storage in a Java
program.
• A variable is defined by the combination of an
identifier, a type, and an optional initializer.
• All variables have a scope, which defines their
visibility.
e.g. int a = 10;
type identifier value

Initialization
• Static Initialization:
variables can be initialized using constants
e.g. char c = ‘M’;
or, char c;
c = ‘M’;
• Dynamic Initialization:
Java allows variables to be initialized dynamically,
using any expression valid at the time the variable is
declared.

class Initialize
{
public static void main(String args[])
{
// a and b are statically initialized
double a = 3.0, b = 4.0;
// c is dynamically initialized
double c = Math.sqrt(a * a + b * b);
System.out.println("Hypotenuse is “ + c);
}
}

Portability Vs Platform Independence
• Portability focuses on adaptation of software in various
OS, by recompiling the source to make the binary
compatible with the target OS and not necessarily
modifying the source.
• Platform independence focuses on ability of software to
run on VIRTUAL hardware that in turn interfaces with
the PHYSICAL hardware.
• Examples of cross-platform or platform independent
languages are Python, JavaScript, Java etc.

L2 datatypes and variables

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