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JavaLanguage Basics
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Keywords
Keywords of Java are given below abstract continue for new
switch
assert*** default goto* packagesynchronized
boolean do if privatethis
break double implements protected throw
byte else import public throws
case enum**** instanceof return transient
catch extends int short trychar final interface static void
class finally long strictfp** volatile
const* float native super while
* not used
** added in 1.2
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Rules for naming Identifiers
Any keyword should not be used as anidentifier.
The name should consist of onlyalphabets, numbers and underscore.
First character should be any alphabet orunderscore.
The name cannot start with a number.
Lowercase and uppercase characters areconsidered as different in C++.
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Basic data Types
In Java data types can be classifiedunder four major categoriesdepending upon the space requiredfor storing data in the memory.
Integers Floating Point Numbers
Characters
Boolean
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Integers
Integers are used to store wholevalued numbers.
All of these are signed, positive ornegative values.
Java does not support unsignedintegers.
Java defines four integer types byte,
short, int and long.
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Integers
Data
Type
Size in
Bytes
Range
byte 1 -128 to 127
short 2 -32768 to 32767
int 4 -2,147,483,648 to 2,147,483,647Long 8 -9,223,372,036,854,775,808 to
9,223,372,036,854,775,807
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Floating Point Numbers
Floating point numbers are also known asreal numbers and are used to storefractional precision values.
ava defines two types of floating pointtypes :
float
double
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Floating Point Numbers
Data
Type
Size in
Bytes
Range
float 4 1.4e-045 to 3.4e+038
double 8 4.9e-324 to 1.8e+308
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Characters
char data type is used to store characters. char is a 16 bit type because Java uses
Unicode to represent characters instead ofASCII.
Unicode is a international character set havingrepresentation of all the character set found inthe dozens of languages like English, Latin,Greek, etc. Therefore to store a character
value in Java we require 2 bytes (16 bits). Therange of a character set is 0 to 65,536.
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Booleans
Booleans are used to store logicalvalues, i.e. true or false.
Boolean data types are used to store thevalues returned by the conditional
expressions, such asi >= j.
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Operators
Operators are used to perform anyarithmetic or logical operations ongiven expressions.
The variables, constants, or values are
joined to build an expression.The variables or constants on which
operator is applied are known as
operands.An operator is applied to one or morethan one expression or operands toget some value.
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Unary vs Binary Operator
Some operators need one operand and someneed two to operate. Unary operatorsrequire one operand to yield result, whilebinary operators require two operands to
operate.For example, in the following expression
40 20
We are using () as a binary operator
because it is operating on two operands, 40and 20.
Lets take another expression
15
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Java Operators
In Java, operators can be divided intofollowing categories
Increment and Decrement Operator Assignment Operator
Arithmetic operators Relational Operators Logical Operators
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Increment / Decrement Operator
The unary operator ++ and -- are used toincrement or decrement the value of anyvariable by 1.
++ is the increment operator and is the
decrement operator.These operators may be used either as
prefix or postfix notations.
In prefix notation, the value of the variableis increased by 1 before the variable isused.
In the postfix notation, the value of the
variable is increased by one after usingthe variable.
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Increment / Decrement Operator
For example, if i = 5, then in the followingexpressions,
j = i++
k = ++i
In the first expression, the value of i willbe assigned to j and then incremented,i.e.
j = 5 and i = 5.
In the second expression, the value of iwill be incremented first and then thisvalue will be assigned to k i.e.
i =5 and k = 5.
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Assignment Operator
Assignment operator is used to assign avalue to any variable. In Java, = sign isused as assignment operator.
For example, in the following expression
a = 10We can assign a single value to more than
one variable in a single expression
a = b = c = 10;
Here, all the three variables, i.e. a, b and care assigned the value 10.
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Assignment Operator
In Java, we should also assign a value to avariable using compound assignmentoperator. For example,
a = a + 10;
Above expression can also be written as,a += 10;
Here, += is a compound assignmentoperator.
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Assignment Operator
Similarly we should used followingcompound operators
a - = 10;
a * = 10;
a / = 10; a % = 10;
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Arithmetic Operator
Arithmetic operators are used to performnumeric calculations on the operands.
There are five arithmetic operators
Operator Description Example
+ Addition a + b
- Subtraction a b
* Multiplication a * b
/ Division a / b
% Modulus (returns the remainder after division) a % b
xamp e:
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xamp e:// Program to display the arithmetic operationspublic class Calc {
public static void main(String args[]) {
int a = 5, b =7, result = 0;result = a + b;System.out.println(Sum = +
result);result = a - b;
System.out.println(Difference = + result);
result = a * b;System.out.println(Dividend = +
result);result = a / b;System.out.println(Remainder =
+ result);}
}
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Relational Operators
Operator Description Example
< Less than a < b
> Greater than a > b
= = Equal to a = = b
! = Not equal to a ! = b
= b
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Logical Operators
Logical operators are used to combineand evaluate two or more expressions.These operators produce 0 or 1 as
result.The logical operator table is given below
Operator Description Example
&& AND (a = = 5) && (b > a)
|| OR (a = = 5) || (b > a)
! NOT ! (a = = 5)
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Expressions
Combination of operands andoperatorsArithmetic expression
a = b + 10;Relational expression
a
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Type Casting
Type Casting refers to changingan entity of one data type intoanother. This is important for thetype conversion in developingany application. If you will storea int value into a byte variabledirectly, this will be illegal
operation. For storing yourcalculated int value in a bytevariable you will have to change
the type of resultant data which
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