Java Syntax

Java Program Structure
Java program structure / Java Syntax   
> Download Java Software (JDK) and Install

> Set Environment (Path) Variable to access Java Run -time Environment from any directory in C drive.

> Download Eclipse software

C:\Program Files\Java\jdk1.8.0_40\bin - Java path

C:\Users\G C Reddy\Desktop\eclipse -Eclipse

How Eclipse communicates with Java Run-time Environment

Using Path Environment variable
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Java Programming
Java Project
    -> Packages
        -> Classes, Interfaces etc...


> Create Java Project in Eclipse

> Create a package

> Create a Class
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Sample Java Program
1) Package Declaration statement
Ex:
package abcd;
----------------------
2) Import Statements
We can import built in and User defined Libraries using import keyword.

Examples for Built in packages

io, jxl, sql etc...

import java.io.Console;

import java.lang.*;

import is java keyword to import Libraries

java - Project

io - package

Console - Class

lang.* - all classes from lang package
-----------------------------
3) Class declaration statement
Ex:
public class Sample {

public - Access Modifier

class - java keyword to declare a class

Sample - Name of the class
---------------------------------
4) Comments section

// This is a Sample Java Program

5) main method statement - Program execution starts from main method
(* It is the mandatory statement in every Java program)

public static void main (String [] args){

public - Access Modifier

static - use main method without invoking any object

void - returns nothing

main method name

6) Declarations
We can declare variables and constants
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System.out.println ("Addition of a, b, c is: "+ (a+b+c));

System - Class

out - Object

println - method

"Addition of a, b, c is: " - Message / Details

+ - Concatenation

a, b, c, d -Variables

Conditional statements
Loop statements
Built in and user defined methodsOperators etc....
------------------------------
Writing Normal statements - every statement should end with ;

Writing blocks - Statements of the block enclosed {}
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Java Program Example:


package abcd;

import java.io.Console;
import java.lang.*;
public class Sample {
    // This is a Sample Java Program
public static void main (String [] args){
    int a = 10, b, c; // Declartion of Variables
    b= 20; // Initialization
        System.out.println (a+b);
    a = 50;
    final int MONEY = 100; // declaring constant
    // MONEY = 200;
    System.out.println ("Addition of a, b, is: "+ (a+b));

    if (b > a){
        System.out.println ("B is a Big Number");
        }
    else
    {
        System.out.println ("A is a Big Number");
    }
for (c=1; c <= 10; c++){
    System.out.println (c);
}   
}
}
--------------------------------------------
Java Comments
Comments are English word, can be used for code documentation.

Purpose of Comments:
a) To make the code Readable

b) To make the code disable from execution

Comments Syntax in Java:
Use // for Single line comment

Use /*....
......
.....
*/ for multiple lines comment
--------------
Ex:

int a = 10, b, c; // Declaration of Variables

// public static void main (String [] args){

----------
/* if (b > a){
        System.out.println ("B is a Big Number");
        }
    else
    {
        System.out.println ("A is a Big Number");
    }
    */

Usage of Comments in Test Automation:
a) To write Test headers

b) To write method headers

c) To explain complex logic

d) To explain resource usage
Etc...
--------------------------------
Java Data Types


What is Data Type?


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

Ex: character, integer, float etc....

> Java supports explicit declaration of Data types.
(we need to specify the data type before declaring the Variable)

Syntax:data_type variable_name;

data_type variable_name = value;

Example:int a;

int a = 100;
----------------------
Two types of Data types in java
a) Primitive Data types

b) Non-primitive Data types / Reference Data types
-----------------------------------
a) Primitive Data types8 primitive data types

Integer types
1) byte (8 bits)

Ex:

byte a =100;

2) short (16 bits)

short a = 10000;

3) int (32 bits)

int a = 100000;

4) long (64 bits)

long a = 100000L
------------------
Rational types (Numbers with decimal places)
5) float (32 bits)

float a = 1.2;

6) double (64 bits)
ex:
double a = 19.3456;
---------------------
Characters
7) char (16 bits)

Ex:

char a ='Z'
------------------------
Conditional
8) boolean (undefined, depends on JVM)

Ex:
boolean a = true
---------------------------------
b) Non-primitive / Reference data types 

Non-primitive data types in Java are Objects and Arrays.

Note:

Reference types are not passed value, passed by reference

Ex:

Button a = new Button("OK")
-----------------------------------------------
Java Variables
 

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 etc...
-------------------------
2) Declaration of Variables
Java Supports explicit declaration of variables

Syntax:

dataType VariableName;

Ex:

int a;
---------------
dataType variable1, variable2, variable3;

Ex:

int a, b, c;
------------------------
dataType VariableName = value;

Ex:

int a =100;
--------------------------
3) Assigning values to variables
a) Initialization

int a;
a=10; // Initialization
--------------
int a=10; // Initialization
----------------
b) Reading
    using Input devices
    from files(text/excel)
    from databases
    from Application objects
-------------------------
4) Types of Variables
a) Instance Variable
A variable that is declared inside the class but outside the method

b) Local variable
A variable that is declared inside the method

c) Static variables
A Variable that is declared as static, It cannot be local.
----------------------
5) Naming Conventions
> Java Variables are case sensitive, monkey is not the as Monkey or MONKEY.

char monkey, Monkey, MONKEY

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

Ex:
myvar
MYVAR
$myvar
_myvar
myvar1
myvar_1
----------
1myvar - invalid
----------------------
> Variable names cannot be equal to java reserved words

Ex:

int
for
import

> Must be unique in the scope of declaration.
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