Today a written test was conducted at Payilagam

1) What is compiler and interpreter

Compiler:
A compiler is a software application that follows the grammar rules of programming languages to translate source code into machine code.

Interpreter (JVM):
An interpreter is computer software that converts programs statements into machine code. Scripts already compiled code and source code all include program statements.
Checks line by line.

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2) Features of Java

Simple

Object oriented

Platform independent

Secure

Robust

Portable

Multithreaded

High performance

Distributed

Dynamic & extensible

Architecture neutral

Interpreted & compiled

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3) What is class and objects.

Class:

A class is a blueprint / template for creating objects.

It defines properties (variables) and behaviors (methods).

Example: Think of a class as a car design.

Object:

An object is an instance of a class.

It is created from a class and represents a real-world entity.

Example: A real BMW car or Audi car made from the design.

Example:
Student = Class

class Student {
String name;
int age;

void display() {
    System.out.println("Name: " + name);
    System.out.println("Age: " + age);
}

}

Main class

public class Main {
public static void main(String[] args) {

    Student s1 = new Student();
    s1.name = "Kiruba";
    s1.age = 20;

    Student s2 = new Student();
    s2.name = "Manoj";
    s2.age = 22;

    s1.display();
    s2.display();
}

}
Student=class

S1,s2=object

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(4) What is Identifiers

All Java variables must be identified with unique names.

These unique names are called identifiers.

Identifiers can be short names (like x and y)

Or more descriptive names (age, sum, totalVolume).

Good:

int minutesPerHour = 60;

Ok, but not so easy to understand:

int m = 60;

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(5) What is Declaration and Initialization

Declaration:

Telling the compiler that a variable exists and its type.

You are reserving memory for it, but not giving it a value yet.

Example:

int num; // declaration (num is an integer variable)

Initialization:

Assigning the first value to a declared variable.

Without initialization, the variable has no defined value.

Example:

num = 10; // initialization (assigning value 10 to num)

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1. What is ASCII and UNICODE?

ASCII

(American Standard Code for Information Interchange)

Old character encoding system

Uses 7 bits (0–127) → 128 characters

Covers only English letters, digits, symbols

Eg.:

A = 65

a = 97

0 = 48

UNICODE

Modern encoding system, developed to represent all world languages

Uses 16 bits or more → can represent 65,536+ characters

Supports English + all languages + emojis + symbols

Eg.:

A = U+0041

a = U+0061

☺ = U+1F600

7.Program (Hierarchical Inheritance)

Super class → Employee

Sub classes → Manager and Developer

1 method → calculateSalary() that returns salary

class Employee {
String name;
int id;

double calculateSalary() 
{
    return 0;
}

}

class Manager extends Employee {
double calculateSalary() {
return 40000; // fixed salary
}
}

class Developer extends Employee {
double calculateSalary() {
return 35000; // fixed salary
}
}

public class Company {
public static void main(String[] args) {
Manager m = new Manager();
m.name = "karan";
m.id = 101;

    Developer d = new Developer();
     d.name = "manoj";
     d.id = 103;

    System.out.println("manager "+ m.name + " (ID: " + m.id + ") Salary: " + m.calculateSalary());
    System.out.println("Employee "+ d.name + " (ID: " + d.id + ") Salary: " + d.calculateSalary());
}

}