Notesale: Turn your study into money

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VARIABLES
In Java, every variable has a type
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Here are some examples:
double salary;

//declaring a single variable salary of type double

int vacationDays;
long earthPopulation;
boolean done;
int i,j;

//declaring multiple variables

Rules for Naming Variable
A variable name must begin with a letter and must be a sequence of letters or
Digits
Java is case sensitive
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You also cannot use a Java reserved word(keyword) as a variable name
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Initializing Variables
After you declare a variable, you must explicitly initialize it by means of an
assignment statement
For Example: If variable is not initialized you get the error as below
int vacationDays;
System
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println(vacationDays); // ERROR--variable not initialized
Example :
int vacationDays; //declaring a variable called vacationDays
VacationDays = 12; // Initializing vacationDays to 12
You can both declare and initialize a variable on the same line
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Types of Variables
There are three types of variables in Java
1
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instance variable
3
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You can use
this variable only within that method and the other methods in the class aren't even aware that the
variable exists
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2) Instance Variable
A variable declared inside the class but outside the body of the method, is called an instance variable
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3) Static variable
A variable that is declared as static is called a static variable
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You can create a single
copy of the static variable and share it among all the instances of the class
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Constants
In Java, you use the keyword final to denote a constant
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Once the value is assigned, it cannot be reassigned
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14; //PI is real constant
int radius =10;
double area;
area= PI*radius*radius;

System
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println("The Area of Circle is " + area);
}
It is probably more common in Java to create a constant so it’s available to multiple methods inside a
single class
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Set up a class constant with the keywords static final
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14;
public static void main(String args[])
{
int radius =10;
double area;
area= PI*radius*radius;
System
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println("The Area of Circle is " + area);
}
}

Operators in Java
Arithmetic Operators: They are used to perform simple arithmetic operations on primitive data
types
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They are used to increment, decrement or
negate a value
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+ :Unary plus, indicates positive value
++ :Increment operator, used for incrementing the value by 1
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Post-Increment : Value is first used for computing the result and then incremented
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-- : Decrement operator, used for decrementing the value by 1
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Post-decrement : Value is first used for computing the result and then decremented
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! : Logical not operator, used for inverting a boolean value
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+=, for adding left operand with right operand and then assigning it to variable on the left
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*=, for multiplying left operand with right operand and then assigning it to variable on the left
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%=, for assigning modulo of left operand with right operand and then assigning it to variable on the left
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They return
boolean result after the comparison
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!=, Not Equal to : returns true if left hand side is not equal to right hand side
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<=, less than or equal to : returns true if left hand side is less than or equal to right hand side
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>=, Greater than or equal to: returns true if left hand side is greater than or equal to right hand side
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&& are also called short circuit operators because they are
optimized
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||, Logical OR : returns true if at least one condition is true
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It has three operands and hence the name
ternary
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Bitwise Operators
 The bitwise operators are &(bitwise AND), |(bitwise OR), ^(bitwise exclusive OR), <<(shift left)
and >>(shift right)
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 Bitwise OR (|)
 This operator is a binary operator, denoted by ‘|’
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e
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 Bitwise AND (&)
 This operator is a binary operator, denoted by ‘&’
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e, if
both bits are 1, it gives 1, else it gives 0
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 For example : a<<2 means multiply a by 2^2(i
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4) which yields 8
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 For example b>>2 means divide b by 2^2(i
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4) which yields 1

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