Java Modifiers, Variables and Operators

Java Modifiers, Variables and Operators

i) Modifiers in Java

ii) Java Variables

iii) Java operators
—————————–
i) Modifiers in Java
Modifiers are keywords that we add to those definitions to change their meaning.

a) Access Modifiers

b) Non-Access Modifiers
————————–
a) Access Modifiers
We use access modifiers to define access control for classes, methods and variables.

Four Access Modifiers

i) private
The private access modifier is accessible only within class.

Ex:

private int a =100;

2) default
If we don’t specify any modifier then it is treated as default, this can be accessible only within package.

class Sample{
.
.
}

3) protected
The protected access modifier is accessible within package, outside of the package but through Inheritance only.

protected class Sample{
.
.
}

4) public
public access modifier is accessible everywhere.

public class Sample {
.
.
}
—————————————————
Modifier
Within Class
Within Package
Outside of the Package
(By Sub Class)
Outside of the Package
private
Y
N
N
N
default
Y
Y
N
N
protected
Y
Y
Y
N
public
Y
Y
Y
Y

b) Non Access Modifiers
1) static
static modifier is used create classes, methods and variables.

Ex:

static int a =10;

static void int add(){
.
.
}

2) final
final modifier for finalizing of classes, methods and variables.

Ex:
final int a =100;
.
.
.
a=200; //Error
—————
int a =100;
.
.
.
.
a =200;
——————
3) abstract
abstract modifier is to create abstract classes, abstract methods

ex:

abstract class Sample{
.
.
}
——————————-
ii) Java Variables
1) What is Variable?
A named memory location to store the temporary data within a program.

Two types of memories in Computer environment

a) Primary memory (RAM)

b) Secondary memory (HDD, DVD, USB drive etc…)
—————————-
2) Declaration of Variables
Java supports Explicit declaration of Variables.

Syntax and Examples:

dataType variableName;

int a;
————-
dataType variablename=value;

int b=20;
—————
dataType variable1, Variable2, variable3;

int a, b, c;
—————–
dataType variable1=value; variable2=value; varible3=value;

int a=10; b=20; c=30;
————————————
3) Assign values to variables
a) Initialization

b) Reading

Ex:

int a=100; //Initialization

int a=10;
int b;
b=a; //Reading
———————————
4) Variable Naming Restrictions
> Java variables are case sensitive,

> Java variable name should start with a letter or $ or _

Ex:

myvar(Correct)
MYVAR
$myvar
_myvar
myvar_1
————–
1myvar(Incorrect)
*myvar
—————-
> Variable names should not match with Java keywords/Reserved words.

> Must be unique in the scope of declaration.

> Variable names Must not exceed 255 characters.
——————————————-
5) Types of Variables
Three types of variables in Java
a) Local variable(Local variable is declared in methods or blocks.)

b) Instance variable(Instance variables are declared in a class but outside of a method or any block)

c) Class/Static variableA Variable that is declared as static, It cannot be local.
———————————-
Example:

package xyza;

public class VariablesExample {
//a Variable is a Class/Static variable
static int a =100;

//mysalary variable is a Local variable.
public int salary(){
int mysalary =10000+2000+1500;
mysalary=mysalary + a;
return mysalary;
}

public static void main (String[]args){
//Instance variable
int b =200;
System.out.println(a);//100
System.out.println(b); //200

VariablesExample obj= new VariablesExample();
System.out.println(obj.salary());
// i is a Local Variable
for (int i=1; i<=5; i++){
System.out.println(i);
System.out.println(a);
System.out.println(b);
}
}
}
———————————-
iii) Java Operators
Important Categories of Operators

a) Arithmetic Operators

b) Relational Operators

c) Assignment Operators

d) Logical Operators
——————————-
a) Arithmetic Operators
1) Addition + (for Addition, String concatenation)

2) Subtraction – (for Subtraction, Negation)

3) Multiplication *

4) Division /

5) Modules %

6) Increment ++

7) Decrement —
—————————
Example:

public class OperatorsExample {
public static void main (String [] args){
int a =10, b=5;
String c =”Selenium”, d= “Testing”;

System.out.println(“Addition of a, b is: “+ (a+b));//Addition of a, b is: 15
System.out.println(“Subtraction of a, b is: “+ (a-b));
System.out.println(“Multiplication of a, b is: “+ (a*b));
System.out.println(“Division of a, b is: “+ (a/b));
System.out.println(“Modules of a, b is: “+ (a%b));

b=10;
a = ++b;
System.out.println(a);//11

b=10;
a = –b;
System.out.println(a);//9
}
}
—————————————
b) Relational Operators
1) ==

2) !=

3) >

4) >=

5) <

6) <=
———————————-
Note: Relational Operators return Boolean / Logical result

Example:

public class OperatorsExample {
public static void main (String [] args){
int a =10, b=20;
System.out.println((a>b));//false
System.out.println((a>=b));//false
System.out.println((a==b));//false

System.out.println((a<b));//true
System.out.println((a<=b));//true
System.out.println((a!=b));//true
}
}
————————————————
d) Logical Operators
1) Logical Not Operator !

2) Logical And Operator &&

3) Logical Or Operators ||

Result Criteria

Not operator
————–
Operand1 Operand2 Result
————————————–
true true false
true false true
false true true
false false true
————————————–
And operator
————–
Operand1 Operand2 Result
————————————–
true true true
true false false
false true false
false false false
————————————–
Or Operator

Operand1 Operand2 Result
————————————–
true true true
true false true
false true true
false false false
————————————–
Example:

public class OperatorsExample {
public static void main (String [] args){
boolean a =true, b=false;
System.out.println(!(a && b));//true
System.out.println((a && b));//false
System.out.println((a || b));//true
}
}
————————————–
public class OperatorsExample {
public static void main (String [] args){
int a =1000, b=500, c=7000;

if ((a>b) && (a>c)){
System.out.println(“A is a Big Number”);
}
else{
System.out.println(“A is Not a Big Number”);
}
}
}
————————————–
c) Assignment Operators
1) Assignment Operator

=

a=10;

2) Add and Assign +=

3) Subtract and assign

4) Multiple and assign
——————————-
Example:
public class OperatorsExample {
public static void main (String [] args){
int a =10;

System.out.println(a);//10
a+=10;
System.out.println(a);//20

a-=10;
System.out.println(a);//10

a*=10;
System.out.println(a);//100
}
}
————————————-
Bitwise Operators
> Java defines several bitwise operators, which can be applied to the integer types, Bitwise operator works
on bits and performs bit-by-bit operation.

i) The bitwise & operator performs a bitwise AND operation.

ii) The bitwise ^ operator performs a bitwise exclusive OR operation.

iii) The bitwise | operator performs a bitwise XOR operation.
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