Java Program Structure and Java Syntax


Java Program Structure and Java Syntax

i) Java Program Structure

ii) A Sample Java Program

iii) Comments in Java

iv) Java Data Types
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Java Environment Setup
 

> Download Java (JDK) Software and Install

> Set Environment Variable (Path variable)

> Download Eclipse IDE and Extract.
--------------------------
Create Java project
    > Create Java Package
        Create Java Class /Program
-----------------------------------------
i) Java Program Structure
 

1) Documentation Section

2) Package declaration Statement

Ex: package xyza;

3) Import Statements

We import built in and User defined libraries using import keyword

Ex:

import java.io.Console;
import java.lang.*;

import - It is a Java keyword to import Libraries.

java -Project

io -Package

Console - Class

lang.*; - import all classes from lang package.
--------------------------------------
4) Class declaration Statement

public class Sample {

}

public - Access Modifier

class - Java keyword to declare a class

Sample - it is the Class name (You can use any meaningful name)
----------------------------------------------
5) main Method (Java 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 - Non-Access Modifier (use main method without invoking any object)

void - Returns nothing

main- method name
-----------------------------------
6) Declarations

We can Declare Variables and Constants.

Other Statements

System.out.println("Hello Selenium");

System - Class (Pre-defined)

out - Object

println - method

"Hello Selenium" - Message
--------------------------------
7) Code blocks

Condition blocks

Loop blocks

Method blocks (method declaration before the main method, but we access methods after main method)
etc...
-------------------------------------
> Every normal statement/step ends with semi colon

> Every code block enclosed with {}
-----------------------------------------
ii) A Sample Java Program
 

//Documentation

package xyza;

import java.io.Console;
import java.lang.*;

public class Sample {

//Create a Method(User defined)
public int multiply(int a, int b, int c){
int result = a * b * c;
return result;
}

public static void main (String [] args){
// This is a sample Program

int a = 10, b, c; //Variables Declaration   
b = 20; c = 30; //Initialization

final int money =100;//Constant Declaration

System.out.println("Addition of a, b is " + (a + b));//Addition of a, b is 30
System.out.println(money);//100
System.out.println(c);//30

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

//Loop block

for (int d=1; d <=10; d++){
    System.out.println(d);
}
//Create Object and access Methods
Sample obj = new Sample();
int x = obj.multiply(10, 25, 50);
System.out.println(x);
}
}
-----------------------------------------
iii) Comments in Java
 

Comments are English words 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

Example:
package xyza;

public class Sample2 {

public static void main (String [] args){
//This is a Sample Program
int a, b, c; //Declaration of variables
a=10; b=20;c=30;
       
/*if (a > b){
System.out.println("A is a Big Number");
}
else {
System.out.println("B is a Big Number");   
}*/

System.out.println(c);
}
}
------------------------------------
Usage of Comments in Test Automation

a) To write Test Case header

b) To write Method header

c) To explain complex logic etc...
-----------------------------------------
iv) Java Data Types
 

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

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

Java Supports Explicit Declaration of Data Types.
(we need to specify the data type before declaring the a Variable or constant etc....)

Syntax:

dataType variableName;

dataType variableName =value;

dataType variable1Name, variable2Name, variable3Name;

Example:

int a;

char b ='A';

int a, b, c;
-----------------------------
Two Types of data Types in Java

a) Primitive Data Types

b) Non-primitive Data Types / Reference Data Types
--------------------------------
a) Primitive Data Types (8 data types)

i) Integer Types
----------------
1) byte (8 bits)

byte a =10;

2) short (16 bits)

short a =10000;

3) integer(32 bits)

int a = 100000;

4) long (64 bits)

long a =100000000000000;
------------------------
ii) Relational types (Numbers with decimal places)

5) float (32 bits)

float a = 1.23;

6) double (64 bits)

double a =123.345654322;
-------------------------------
iii) Characters

7) character

char a ='Z'
----------------------------
iv) Conditional

8) Boolean

boolean a = true;
------------------------------
b) Non-primitive Data Types / Reference Data Types

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

ex:

Button a = new Button("OK")
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