DEV Community

Abhishek Gupta
Abhishek Gupta

Posted on • Edited on

πŸš€ Java Crash Course (CIITM Dhanbad BCA 4th Sem) β€” From Zero to Exam Ready

Prepared from previous year papers of MCU.

Based on:

  • 2022 Previous Year Paper
  • 2023 Previous Year Paper
  • 2025 Previous Year Paper

These notes are:

  • Beginner friendly
  • Exam focused
  • Previous-year based
  • Easy English
  • Long answer + short answer style
  • Important question tagged

πŸ”– TAG LEGEND

Tag Meaning
⭐⭐⭐⭐ Very Very Important (Repeated in exams)
⭐⭐⭐ Important
πŸ”₯ High chance for this year
⚠️ Common Viva Question
πŸ’» Important Program
πŸ“ Theory Question
❓ Frequently Asked Question

🚨 Didn’t study Java all semester?

This guide will take you from zero β†’ exam-ready β†’ confident pass in a few days.

🎯 HOW TO USE THIS

Day Topics
Day 1 Unit 1
Day 2 Unit 2
Day 3 Unit 3
Day 4 Unit 4 + Unit 5
Day 5 Full Revision + Programs

πŸ‘‰ Focus mainly on:

  • ⭐⭐⭐⭐ Topics
  • Previous year questions
  • Important programs

🧠 UNIT I β€” JAVA BASICS

βœ… Introduction to Java πŸ”₯β­β­β­β­πŸ“

Definition

Java is a:

  • High-level
  • Object-oriented
  • Secure
  • Platform-independent programming language.

Developed by James Gosling at Sun Microsystems.

βœ… Features of Java πŸ”₯β­β­β­β­πŸ“

Important Features

  1. Platform Independent
  2. Object Oriented
  3. Secure
  4. Robust
  5. Portable
  6. Multithreaded
  7. Distributed
  8. Dynamic

βœ… Difference Between Java and C++ πŸ”₯⭐⭐⭐⭐❓

C++ Java
Platform dependent Platform independent
Uses pointers No pointers
Manual memory management Automatic garbage collection
Faster Slightly slower
Supports operator overloading No operator overloading
Uses compiler only Uses JVM

βœ… Can C++ Program Run in Java Environment? πŸ”₯❓

Answer

No.

Reason:

  • C++ creates machine code.
  • Java creates bytecode.
  • Java programs require JVM.

βœ… History of Java β­β­β­πŸ“

Important Points

  • Developed in 1995
  • Created by James Gosling
  • Original name: Oak
  • Later renamed to Java

βœ… Java Editions ⭐⭐⭐

Edition Work
Java SE Desktop Applications
Java EE Enterprise Applications
Java ME Mobile Applications

βœ… Java Environment πŸ”₯β­β­β­β­πŸ“

Component Full Form Work
JDK Java Development Kit Development
JRE Java Runtime Environment Execution
JVM Java Virtual Machine Runs bytecode

βœ… JVM (Java Virtual Machine) πŸ”₯⭐⭐⭐⭐❓

Definition

JVM is a virtual machine that executes Java bytecode.

Functions of JVM

  1. Executes bytecode
  2. Makes Java platform independent
  3. Memory management
  4. Garbage collection
  5. Security

JVM Architecture ⭐⭐⭐⭐ 

Java Source Code
        ↓
Compiler (javac)
        ↓
Bytecode (.class)
        ↓
JVM
        ↓
Machine Code
        ↓
Output
Enter fullscreen mode Exit fullscreen mode

βœ… JIT Compiler ⚠️⭐⭐⭐

Definition

JIT (Just In Time) compiler converts bytecode into machine code quickly during execution.

βœ… Bytecode ⚠️⭐⭐⭐

Definition

Intermediate code generated by Java compiler.

Extension:

.class
Enter fullscreen mode Exit fullscreen mode

βœ… Java Program Structure πŸ”₯β­β­β­β­πŸ’» 

class Main {

    public static void main(String args[]) {

        System.out.println("Hello Java");
    }
}
Enter fullscreen mode Exit fullscreen mode

Explanation

Part Work
class Defines class
main() Entry point
System.out.println() Prints output

βœ… Tokens β­β­β­πŸ“

Definition

Smallest unit of Java program.

Types

  • Keywords
  • Identifiers
  • Literals
  • Operators
  • Separators

βœ… Data Types ⭐⭐⭐

Type Example
int 10
float 10.5
char 'A'
boolean true

βœ… Variables and Constants ⭐⭐⭐

Variable

Value changes.

int a = 10;
Enter fullscreen mode Exit fullscreen mode

Constant

Uses final keyword.

final int a = 10;
Enter fullscreen mode Exit fullscreen mode

βœ… Type Casting ⭐⭐⭐ 

int a = (int)10.5;
Enter fullscreen mode Exit fullscreen mode

βœ… Operators πŸ”₯⭐⭐⭐

Types

  • Arithmetic
  • Relational
  • Logical
  • Assignment
  • Unary
  • Bitwise

βœ… Decision Making ⭐⭐⭐

if Statement 

if(x > 0) {
    System.out.println("Positive");
}
Enter fullscreen mode Exit fullscreen mode

switch Statement ⭐⭐⭐ 

switch(day) {

    case 1:
        System.out.println("Monday");
        break;
}
Enter fullscreen mode Exit fullscreen mode

βœ… Loops πŸ”₯β­β­β­β­πŸ’»

for Loop 

for(int i=0;i<5;i++) {

    System.out.println(i);
}
Enter fullscreen mode Exit fullscreen mode

while Loop 

while(i<5) {

    i++;
}
Enter fullscreen mode Exit fullscreen mode

do-while Loop 

do {

    i++;

} while(i<5);
Enter fullscreen mode Exit fullscreen mode

βœ… Jump Statements ⭐⭐⭐

  • break
  • continue
  • return

βœ… Labeled Loop ⭐⭐⭐ 

outer:
for(int i=0;i<3;i++) {

    for(int j=0;j<3;j++) {

        break outer;
    }
}
Enter fullscreen mode Exit fullscreen mode

🧠 UNIT II β€” OOP IN JAVA

βœ… OOP Concepts πŸ”₯β­β­β­β­πŸ“

  1. Class
  2. Object
  3. Inheritance
  4. Polymorphism
  5. Encapsulation
  6. Abstraction

βœ… Class and Object πŸ”₯β­β­β­β­πŸ’»

Definition

Class is blueprint of object.

Object is instance of class.

Example 

class Student {

    int age;
}
Enter fullscreen mode Exit fullscreen mode

βœ… Constructor πŸ”₯β­β­β­β­πŸ’»

Definition

Special method used to initialize objects.

Types of Constructor

  1. Default Constructor
  2. Parameterized Constructor
  3. Copy Constructor (conceptual)

Example 

class Demo {

    Demo() {

        System.out.println("Constructor");
    }
}
Enter fullscreen mode Exit fullscreen mode

βœ… this Keyword ⭐⭐⭐πŸ”₯

Definition

Used to refer current object.

this.variable;
Enter fullscreen mode Exit fullscreen mode

βœ… Method Overloading πŸ”₯β­β­β­β­πŸ’»

Definition

Same method name with different parameters.

Example 

class Demo {

    void add(int a,int b) {}

    void add(int a,int b,int c) {}
}
Enter fullscreen mode Exit fullscreen mode

βœ… Static Members ⭐⭐⭐

Shared by all objects.

static int count;
Enter fullscreen mode Exit fullscreen mode

βœ… Inheritance πŸ”₯β­β­β­β­πŸ“

Definition

Acquiring properties of parent class.

Types of Inheritance ⭐⭐⭐⭐

  1. Single Inheritance
  2. Multilevel Inheritance
  3. Hierarchical Inheritance
  4. Hybrid Inheritance
  5. Multiple Inheritance (through interface)

Example 

class A {}

class B extends A {}
Enter fullscreen mode Exit fullscreen mode

Advantages of Inheritance ⭐⭐⭐

  • Code reuse
  • Easy maintenance
  • Reduces duplication

βœ… Constructor in Inheritance πŸ”₯⭐⭐⭐

Parent constructor executes first.

βœ… super Keyword ⭐⭐⭐πŸ”₯

Used to call parent constructor or method.

super();
Enter fullscreen mode Exit fullscreen mode

βœ… Method Overriding πŸ”₯β­β­β­β­πŸ’»

Definition

Child class modifies parent class method.

Difference Between Overloading and Overriding πŸ”₯⭐⭐⭐⭐

Overloading Overriding
Same class Different class
Different parameters Same parameters
Compile time Runtime

βœ… final Keyword πŸ”₯⭐⭐⭐⭐

final Variable

Cannot change value.

final Method

Cannot override.

final Class

Cannot inherit.

βœ… Abstract Class πŸ”₯β­β­β­β­πŸ“

Definition

Class declared using abstract keyword.

Features

  • Cannot create object
  • Contains abstract methods
  • Used for abstraction

βœ… Visibility Control ⭐⭐⭐⭐

Modifier Access
public Everywhere
private Within class
protected Package + subclass
default Within package

🧠 UNIT III β€” ARRAYS, STRINGS, INTERFACES, PACKAGES

βœ… Arrays πŸ”₯β­β­β­β­πŸ’»

Definition

Stores multiple values of same datatype.

One Dimensional Array 

int arr[] = {1,2,3};
Enter fullscreen mode Exit fullscreen mode

Two Dimensional Array πŸ”₯⭐⭐⭐ 

int arr[][] = {

    {1,2},
    {3,4}
};
Enter fullscreen mode Exit fullscreen mode

Difference Between 1D and 2D Array ⭐⭐⭐

1D 2D
Single row Rows and columns
One index Two indexes

βœ… Strings ⭐⭐⭐⭐ 

String s = "Java";
Enter fullscreen mode Exit fullscreen mode

Important String Methods ⭐⭐⭐

Method Work
length() Length
toUpperCase() Uppercase
charAt() Character access
equals() Compare strings

βœ… Vector πŸ”₯β­β­β­β­πŸ“

Definition

Vector is a dynamic array.

Features

  • Dynamic size
  • Synchronized
  • Stores objects

Difference Between Vector and Array πŸ”₯⭐⭐⭐⭐

Vector Array
Dynamic Fixed size
Slow Fast
Synchronized Not synchronized

βœ… Wrapper Classes πŸ”₯⭐⭐⭐⭐

Definition

Convert primitive datatype into objects.

Primitive Wrapper
int Integer
double Double
char Character

Wrapper Class vs Interface ⭐⭐⭐πŸ”₯

Wrapper Class Interface
Converts datatype into object Used for abstraction
Example: Integer Example: Runnable

βœ… Interfaces πŸ”₯β­β­β­β­πŸ“

Definition

Collection of abstract methods.

Syntax 

interface A {

    void show();
}
Enter fullscreen mode Exit fullscreen mode

Advantages

  • Multiple inheritance
  • Abstraction
  • Security

Defining vs Extending Interface πŸ”₯⭐⭐⭐⭐

Defining Interface Extending Interface
Creates interface Inherits interface
Uses interface keyword Uses extends keyword

βœ… Packages πŸ”₯β­β­β­β­πŸ“

Definition

Collection of related classes and interfaces.

Types of Package

  1. System Package
  2. User Defined Package

System Package Examples 

java.lang
java.util
java.io
Enter fullscreen mode Exit fullscreen mode

User Defined Package 

package mypackage;
Enter fullscreen mode Exit fullscreen mode

Advantage of System Package over User Defined Package πŸ”₯⭐⭐⭐⭐

System Package User Defined Package
Predefined Created by programmer
Secure Less secure
Tested User managed

🧠 UNIT IV β€” THREADS

βœ… Thread πŸ”₯β­β­β­β­πŸ“

Definition

Thread is a lightweight process used for multitasking.

Advantages of Thread ⭐⭐⭐

  • Faster execution
  • Better CPU usage
  • Multitasking

Creating Thread πŸ”₯β­β­β­πŸ’» 

class A extends Thread {

    public void run() {

        System.out.println("Thread");
    }
}
Enter fullscreen mode Exit fullscreen mode

Runnable Interface πŸ”₯⭐⭐⭐ 

class A implements Runnable {

    public void run() {

        System.out.println("Thread");
    }
}
Enter fullscreen mode Exit fullscreen mode

Thread Life Cycle πŸ”₯⭐⭐⭐⭐

  1. New
  2. Runnable
  3. Running
  4. Waiting
  5. Dead

Synchronization πŸ”₯⭐⭐⭐⭐

Controls multiple threads accessing same resource.

🧠 UNIT V β€” APPLETS

βœ… Applet πŸ”₯β­β­β­β­πŸ“

Definition

Applet is a small Java program that runs inside browser.

Features of Applet ⭐⭐⭐

  • GUI based
  • Event driven
  • Browser execution

Local Applet vs Remote Applet πŸ”₯⭐⭐⭐⭐

Local Applet Remote Applet
Stored locally Downloaded from internet

Applet vs Application πŸ”₯⭐⭐⭐⭐

Applet Application
Runs in browser Runs standalone
Needs HTML No HTML
Less secure More powerful

Applet Life Cycle πŸ”₯⭐⭐⭐⭐

  1. init()
  2. start()
  3. paint()
  4. stop()
  5. destroy()

Applet Example πŸ’»β­β­β­β­ 

import java.applet.Applet;
import java.awt.Graphics;

public class Demo extends Applet {

    public void paint(Graphics g) {

        g.drawString("Hello Applet",100,100);
    }
}
Enter fullscreen mode Exit fullscreen mode

Applet Tag ⭐⭐⭐ 

<applet code="Demo.class" width="300" height="300">
</applet>
Enter fullscreen mode Exit fullscreen mode

Passing Parameters in Applet ⭐⭐⭐

Uses HTML parameters.

Getting Input in Applet ⭐⭐⭐

Using:

  • TextField
  • Button
  • Label

🧠 EXTRA IMPORTANT TOPICS (MISSED BY MANY STUDENTS)

βœ… Garbage Collection πŸ”₯⭐⭐⭐⭐

Definition

Automatic memory cleanup process.

Example 

System.gc();
Enter fullscreen mode Exit fullscreen mode

βœ… Exception Handling πŸ”₯β­β­β­β­πŸ“

Definition

Handling runtime errors.

Keywords

  • try
  • catch
  • finally
  • throw
  • throws

Example 

try {

    int a = 10/0;
}

catch(Exception e) {

    System.out.println(e);
}
Enter fullscreen mode Exit fullscreen mode

βœ… Multithreading vs Multitasking ⭐⭐⭐

Multithreading Multitasking
Multiple threads Multiple programs
Inside process Multiple applications

βœ… API ⚠️⭐⭐⭐

Application Programming Interface.

Collection of predefined classes and methods.

πŸ”₯ MOST IMPORTANT THEORY QUESTIONS

  1. Difference Between Java and C++ ⭐⭐⭐⭐
  2. JVM Architecture ⭐⭐⭐⭐
  3. Java Program Structure ⭐⭐⭐⭐
  4. Constructor ⭐⭐⭐⭐
  5. Method Overloading ⭐⭐⭐⭐
  6. Method Overriding ⭐⭐⭐⭐
  7. Inheritance ⭐⭐⭐⭐
  8. Interface ⭐⭐⭐⭐
  9. Abstract Class ⭐⭐⭐⭐
  10. Arrays ⭐⭐⭐⭐
  11. Vector vs Array ⭐⭐⭐⭐
  12. Applet Life Cycle ⭐⭐⭐⭐
  13. Thread Life Cycle ⭐⭐⭐⭐
  14. Package in Java ⭐⭐⭐⭐
  15. Wrapper Classes ⭐⭐⭐⭐
  16. Exception Handling ⭐⭐⭐⭐
  17. Garbage Collection ⭐⭐⭐⭐

πŸ”₯ VERY IMPORTANT PROGRAMS πŸ’»

  1. Factorial Program ⭐⭐⭐⭐
  2. Prime Number ⭐⭐⭐⭐
  3. Fibonacci Series ⭐⭐⭐⭐
  4. Palindrome Number ⭐⭐⭐⭐
  5. Array Program ⭐⭐⭐⭐
  6. Constructor Program ⭐⭐⭐⭐
  7. Inheritance Program ⭐⭐⭐⭐
  8. Thread Program ⭐⭐⭐⭐
  9. Applet Program ⭐⭐⭐⭐
  10. Method Overloading Program ⭐⭐⭐⭐

πŸš€ FINAL EXAM STRATEGY

Theory Paper

βœ… Write definition first
βœ… Draw diagrams
βœ… Use headings
βœ… Underline keywords
βœ… Write syntax
βœ… Add examples

Practical Paper

Practice:

  • Arrays
  • Constructors
  • Threads
  • Applets
  • Inheritance
  • Exception handling
  • Overloading
  • Overriding

πŸš€ FINAL MESSAGE

You do not need full semester study now.

You need:

  • Smart revision
  • Important topics
  • Previous year focus
  • Program practice

Top comments (0)