Java Tutorial 2

(Comments in Java, Java Data Types, Java Modifiers, Java Variables and Operators in Java)

I) Comments in Java

Comments are English words, can be used for code documentation.

Purpose of Comments:
a) To make the code Readable

b) To make the code disable form execution

Comments Syntax in Java:
Use // for single line Comment or partial line as comment

Use /* statements
———-
———–
———-
*/ for multiple lines comment

Or
In Eclipse

Select statements
Source menu -> Add Block Comment

Uncomment:
Select Comment block
Source menu -> Remove comment block
————————————-
Usage of Comments in Test Automation
a) To write Test case headers

b) To write Method headers

c) To explain complex logic

d) To explain resource usage
——————————
Example:
public class Comments {

public static void main (String [] args){
int a = 10, b, c; // Declaration of Variables
// It is a Sample Program
System.out.println(a);// 10
b = 50;
c = 2;
/*if (a > b) {
System.out.println(“A is a Big Number”);
}
else {
System.out.println(“B is a Big Number”);
}*/
}
}
—————————————

II) Java Data Types

Data type is a classification of the type of data that a variable or object can hold in Computer programming.

Example:

Character, Integer, String, float etc…

Java supports explicit declaration of Data types.
(We need to specify the data type before declaration of variables.)

Syntax:

dataType VariableName

Example:

int a;
or
int a = 100;
————————————-
In Java we have two types of Data types.

i) Primitive Data types

ii) Non -primitive Data types
——————————
i) Primitive Data types (8 data types)
Integer Data types
———————
1) byte (8 bits)
Example:

byte a = 10;

2) short (16 bits)

Ex:

short b = 10000;

3) int (32 bits)

int c = 100000;

4) long (64 bits)

Ex:

long d = 100000L
—————————–
Rational Data types (Numbers with decimal places)

5) float (32 bits)
Ex:

float a = 1.2;

6) double (64 bits)

Ex:

double b = 19.234567;
———-
Characters

7) char (16 bits)

Ex:

char a = ‘Z’
——————-
Conditional

8) Boolean

Ex:

boolean a = true;
——————————–
ii) Non -primitive Data types
Non -primitive Data types in Java are objects and Arrays.

Ex:

Button = new Button(“OK”)
——————————————–
III) Java Modifiers

Modifiers are keywords that we add to those definitions to change their meanings.

Two types of modifiers in Java:

i) Access Modifiers

ii) Non Access Modifiers
——————————-
i) Access Modifiers
We use Access modifiers to define Access control for classes, methods and variables.

There are 4 types of Access modifiers in Java

1) Private

The private access modifier is accessible only within class.

Ex:

class Abc {
private int a = 100;
.
.
.
}
————————–
2) default

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

Ex:
class Sample{
int a = 10;
.
.
}
———————————–
3) protected

The protected access modifier is accessible within package and out side of the package but
through Inheritance only.
—————————–
4) public

public access modifier is accessible everywhere.

Ex:

public class Abc{
.
.
}
————————————————–
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
———————————————————————————
ii) Non Access modifiers

1) static

static modifiers are used to create class variable and class methods which can be accessed without instance of a class.

Ex:

class A {
static String name = “Selenium”;
}
———————
2 final
final modifier for finalizing the implementation of classes, methods and variables.

class A {
int a = 10;
final int b = 20;
.
.
a = 30;
b = 50;//Incorrect
}
——————–
3) abstract

abstract modifier is to create abstract classes and abstract methods.

Ex:

abstract sample {
Statements
——–
———
——
}
——————
4) synchronized
——————————–

IV) Variables in Java

1) What is Variable?
A named memory location to store or hold the data.

Two types of memory in computer environment:

i) Primary memory – RAM

ii) Secondary memory -ROM

Ex: CD, DVD, HDD, USB drive etc…
———————
2) Declaration of Variables
Syntax:

dataType variableName;

Ex:

int a;
—————–
dataType varaible1, variable2, varaible3;

ex:

int a, b, c;
———————-
dataType variableName = value;

Ex:

int a = 100;
————————–
3) Assigning values to variables
i) Initialization

Ex:
int a;
a = 100;

ii) Reading
using input devices
from files (text, excel)
from databases
from Application objects
——————————–
4) Types of Variables
In Java we have 3 types of variables.

i) Instance variables
A variable that is declared inside the class but outside the method.

ii) Local variables
A variable that is declared inside the Method.

iii) Static / class variables
A variable that is declared as static, It cannot be local.
——————————
5) Naming Restrictions

i) Java variables are case sensitive, monkey is not the as MONKEY or Monkey.

ii) Java variable name must start with a letter or $ or _
Embedded periods can’t be used.

Example:

myvar
MYVAR
$myvar
_myvar
myvar1
myvar_1
———–
my var
my.var
1myvar
*myvar
my-var
———————–
iii) Variable names cannot be equal to Java reserved words.

Ex:
int
for
import
——————-
iv) Must be unique in the scope of declaration.
——————————————–
Variables example:

public static void main (String [] args){
// Variable Declaration
int a;
a = 10; // Initialization
// Declaration of multiple variables in a statement
int b, c, d;
b = 20;
c = 30;
d = 40;
// Declaration of multiple variable and Assigning values.
int e = 50, f=60, g = 70;
char x =’A’;
double y = 2.345;
String z = “Selenium123”;
System.out.println(a);
System.out.println(b);
System.out.println(c);
System.out.println(d);
System.out.println(e);
System.out.println(f);
System.out.println(g);
System.out.println(x);
System.out.println(y);
System.out.println(z);
}
}
———————————————–
V) Java Operators

Operators are used to perform mathematical, Comparison and Logical operations.

Important categories of Operators:

i) Assignment Operators

ii) Arithmetic operators

iii) Relational operators

iv) Logical Operators
etc…
————————————-
i) Assignment Operators
1) Assignment operator =

a = 10;

2) Add and Assign Operator +=

a = 10;

a += 20;

3) Subtract and Assign -=

a = 10;

a -= 5;

4) Multiply and Assign *=

a = 10

a *= 5;
————————————–
Example:
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 *= 5;
System.out.println(a);//50
}
}
————————————–
ii) Arithmetic Operators
Arithmetic Operators return value based Result.

1) Addition + (for Addition and String concatenation)

2) Subtraction – (for Subtraction and negation)

3) Multiplication *

4) Division /

5) Modules %

6) Increment ++

7) Decrement —
——————————-
Example:

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(“Concatenation of c, d is: ” + (c+d)); //Concatenation of c, d is: Selenium Testing

System.out.println(“Subtraction of a, b is: ” + (a-b)); // 5
System.out.println(“Multiplication of a, b is: ” + (a*b)); // 50
System.out.println(“Divison of a, b is: ” + (a/b)); //2
System.out.println(“Modulas of a, b is: ” + (a%b)); //0

a = ++b;
System.out.println(a); //6
b = 5;
a = –b;
System.out.println(a);//4
b =5;
a = b+4;
System.out.println(a); //9
b = 5;
a = b-4;
System.out.println(a);//1
}
}
—————————————
iii) Relational Operators
Relational operators return boolean or logical result (true or false)

1) ==

2) !=

3) >

4) >=

5) <

6) <=
——————————
Example:
public class OperatorsExample {
public static void main (String [] args){
int a = 10, b = 20;
System.out.println(“a > b is ” + (a>b)); //False
System.out.println(“a >= b is ” + (a >= b)); //False

System.out.println(“a < b is ” + (a<b)); //True
System.out.println(“a <= b is ” + (a <= b)); //True

System.out.println(“a == b is ” + (a == b)); //False
System.out.println(“a != b is ” + (a != b)); //True
}
}
——————————————
iv) Logical Operators
1) Logical Not operator !

2) Logical And Operator &&

3) Logical Or operator ||
——————————–
Result Criteria for Not operator
Operand 1 Operand 2 Result
—————————————-
true true false
true false true
false true true
false false true
—————————————–
Result Criteria for Add operator
Operand 1 Operand 2 Result
—————————————-
true true true
true false false
false true false
false false false
—————————————–
Result Criteria for Or operator
Operand 1 Operand 2 Result
—————————————-
true true true
true false true
false true true
false false false
—————————————–
Example 1:
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
}
}
———————————-
Example 2:
public class OperatorsExample {
public static void main (String [] args){
int a = 100, b = 500, c = 700;
if ((a > b) && (a > c)) {
System.out.println(“A is a Big Number”);
}
else
{
System.out.println(“A is Not a Big Number”);
}
}
}
—————————————–
public static void main (String [] args){
int a = 100, b = 500, c = 700;
if (!(a > b) && !(a > c)) {
System.out.println(“A is a Big Number”);
}
else
{
System.out.println(“A is Not a Big Number”);
}
}
—————————
public static void main (String [] args){
int a = 100, b = 50;
if (! (a > b)) {
System.out.println(“A is a Big Number”);
}
else
{
System.out.println(“B is a Big Number”);
}
}
————————————————
Java Flow Control statements
Conditional statements
Loop statements
————————————-
VI) Java Conditional Statements