Java Syntax and Program Structure
Java Syntax and Program Structure, Java Environment setup, Java Language Fundamentals, Writing Java statements, Java coding standards, and Java code blocks.
Java Syntax
1. Java is a case sensitive language
Note: All Java keywords and reserved words are small letters
(if, for, public, main, true, false, null…)
2. First letter of the Java class name should be in upper case
sample //Incorrect
Sample //Correct
Firstprogram //Correct
FirstProgram ////Correct
3. Java Method names should start with lower case
Example:
adminLogin()
4. Java program file name should exactly match with the class name
5. Java program execution starts from main method, which is mandatory in every Java program
6. Every statement /step should end with a semicolon (;)
7. Code blocks (conditional, Loop, Method, etc.) enclosed with {},
8. Java supports Explicit declaration of Data Types
In Java,
int sno =123;//Correct
int x;//Correct
char a=’A’; //Correct
boolean y=true;
abc =100; //Incorrect
In VBScript
Dim city
city =100
.
city =”India”
.
city=1.23
.
city=#10/10/2010#
9. Java supports Explicit declaration of Variables
In Java:
int a, b;
a=10;
b=20;
c=30;//Incorrect
In VBScript
Dim a
a=100
b=200 ‘Correct
Java Syntax and Program Structure
Java Program Structure
1. Documentation Section
It includes comments to tell the program’s purpose, it improves the readability of the Program
2. Package Statement
package abcd;
3. Import statement/s
We import predefined and user-defined libraries using “import” keyword
Example:
import java.util.Scanner;
java – Project
util – Package
Scanner – Class
import java.util.*; // Importing all classes from a package
4. Class Definition
Ex:
public class Sample{
}
5. Interface Section
In this section, we create/declare Static variables, and create/declare Methods
6. main() Method
Java program execution starts from main() method, which is mandatory in every Java program.
public static void main (String [] args){
//Code
}
public – Access Modifier
static – Non Access Modifier (use main method without invoking an object)
void – Returns Nothing
main – Predefined Identifier(Method name)
——————————————-
//Within Main method
main method{
//Main Program
Creating Object/s
ClassName objectName = new ClassName();
Comments
Declarations….(Variable with Data Types, Constants/Final Variables)
Normal Statements
int a;//Declaration
a=100;//Initialization
int b=a;//Reading
System.out.println(10+20); //Print Statement
final int x=100;
if (){ //Condition Code Block
.
}
for (){ //Loop Code Block
.
}
}
Java Syntax and Program Structure
Sections of Java Program
1. Documentation Section – Optional
2. Package Statement – Mandatory
3. Import Statement/s – Depends on our program requirement
4. Class Definition { //Mandatory
5. Interface Section //Depends on our program requirement
6. main method(){
//Main Program contains normal statements and code blocks
Object Creation //Depends on our program requirement
Declarations/Initialization/Reading – normal statements
Operations, Display statements, etc…
Code Blocks, Conditions/Decision-making blocks, Loop Blocks, Constructor Block., Etc…
}
Interface Section //Depends on our program requirement
}
Core Java Step by Step Tutorial
Java Program Example
//This program is for explaining Java Syntax and program Structure.
package abcd;
import java.util.Scanner;
public class Sample {
//Create a Non static method with arguments and return a value
public int add(int a, int b) {
int result;
result=a+b;
return result;
}
//Create a Non static method without arguments and returns Nothing
public void sub() {
int x=100;
int y=50;
System.out.println(x-y);
}
//Create a Static method with arguments and return a value
public static int multiply(int num1, int num2) {
int result= num1*num2;
return result;
}
//Create a Static method without arguments and returns Nothing
public static void comparision() {
int x=100, y=50;
if (x>y) {
System.out.println(“X is Big Number”);
}
else {
System.out.println(“Y is Big Number”);
}
}
public static void main (String [] args){
Scanner scan = new Scanner (System.in);
System.out.println(“Enter Your Name”);
String myName = scan.nextLine();
System.out.println(“My Name is: ” + myName);
int a; //Variable Declaration
a=100;
int b=200; // Variable Declaration with Initialization
char x=’Y’;
String myCountry = “India”;
int c, d, e; //Declaring multiple variables
int f=20, g=40, h=60; //Declaring multiple variables with Initialization
final int price=100;
if (a>b)
{
System.out.println(“A is Big Number”);
}
else
{
System.out.println(“B is Big Number”);
}
System.out.println(“”);
for (int i=1; i<=10; i++)
{ // Print 1 to 10 Numbers
System.out.println(i);
}
System.out.println(“”);
int i=1;
while (i<=5) {
System.out.println(i);
i++;
}
System.out.println(“My Output”);
//Print 1 to 5 Numbers except 4
for (int j=1; j<=5; j++) {
if (j!=4) {
System.out.println(j);
}
}
//Create Object and call nonstatic methods
Sample obj = new Sample();
int val = obj.add(100, 200);
System.out.println(val);//300
System.out.println(obj.add(10, 20));//30
obj.sub();//50
//Call Static methods
val = multiply(10, 40);
System.out.println(val);//400
comparision();//X is Big Number
}
}
