Java concepts for Beginners to Advanced

Overview of Java

Java is a high-level, object-oriented programming language widely used for building platform-independent applications. It is known for its versatility, security, and performance. Java’s motto “Write Once, Run Anywhere” (WORA) ensures compatibility across different platforms, making it a top choice for enterprise-level development.

Overview of Java
Introduction to Java
History of Java
Java vs C++ vs Python
How to Download and Install Java?
Setting Up the Environment in Java
How to Download and Install Eclipse on Windows?
Java Development Kit (JDK)
JVM and its Architecture
JDK Vs JRE Vs JVM
Just In Time Compiler
JIT Vs JVM
Byte Code Vs Machine Code
Basics of Java
Java Basic Syntax
First Java Program (Hello World)
Datatypes in Java
Primitive Vs Non-Primitive Datatypes
Java Identifiers
Operators in Java
Java Variables
Java Keywords
Scope of Variables
Wrapper Classes in Java
Input/Output in Java
How to take Input from users in Java
Scanner class in Java
BufferedReader class in Java
Scanner vs BufferedReader in Java
Ways to Read Input from Console in Java
Print Output in Java
print() Vs println() in Java
Formatted Outputs in Java
Flow Control in Java
Decision making in Java
If Statement in Java
If-Else Statement in java
If-Else-If Ladder in Java
Loops in Java
For Loop
While Loop
Do While Loop
For Each Loop
Continue Statement in Java
Break Statement in Java
Return Statement in Java
Arrays in Java
Strings in Java
OOPS in Java
Classes in Java
Interfaces in Java
Methods in Java
Packages in Java
Collection Framework in Java
Memory Allocation in Java
Exception Handling in Java
Multithreading in Java
Synchronization in Java
File Handling in Java
Java Regex
Java IO
Java Networking
Java SE 8 Features
Java Date & Time
Java JDBC
Java Miscellaneous
Java 17 New Features
Core Java Interview Questions
Java Multiple Choice Questions

1. Introduction to Java

Java is a class-based, object-oriented programming language designed to have as few implementation dependencies as possible. It allows developers to build applications that can run on any platform that supports Java without needing to recompile the code.

2. History of Java

Java was developed by James Gosling at Sun Microsystems (later acquired by Oracle) and released in 1995. Initially created as a language for interactive television, it soon evolved into a general-purpose programming language. The official release of Java ushered in a new era of portability and cross-platform development.

3. Java vs C++ vs Python

Java: Known for its WORA principle, object-oriented design, and robust security features.
C++: Offers better control over system resources but lacks Java’s platform independence.
Python: A dynamically typed language with a simple syntax but slower performance compared to Java.

4. How to Download and Install Java?

Visit the official Oracle website.
Choose the appropriate version of Java for your operating system.
Download and install the JDK (Java Development Kit).
Follow the on-screen instructions for installation.

5. Setting Up the Environment in Java

After installing the JDK, set up environment variables:
1. Go to System Properties → Advanced → Environment Variables.
2. Add a new system variable named JAVA_HOME with the JDK installation path.
3. Edit the Path variable and add the path to the bin folder inside your JDK installation.

6. How to Download and Install Eclipse on Windows?

Visit the official Eclipse website.
Download the latest version for your system.
Extract and run the installer.
Choose the Eclipse IDE for Java Developers package.
Complete the installation process and launch Eclipse.

7. Java Development Kit (JDK)

The JDK includes development tools such as the compiler (javac), the Java runtime (java), and various other utilities necessary to develop and run Java applications.

8. JVM and Its Architecture

The Java Virtual Machine (JVM) is the core of Java’s cross-platform capabilities. It provides the environment for executing Java bytecode and manages system resources such as memory.

JVM Components:

ClassLoader: Loads class files.
Runtime Data Area: Divided into Heap, Stack, Method Area, etc.
Execution Engine: Executes the bytecode.
Native Interface: Allows interaction with native applications.

9. JDK Vs JRE Vs JVM

JDK (Java Development Kit): Includes JRE and development tools.
JRE (Java Runtime Environment): Contains the JVM and class libraries for running applications.
JVM (Java Virtual Machine): Executes bytecode.

10. Just In Time Compiler

The Just In Time (JIT) Compiler is part of the JVM that improves performance by compiling bytecode into native machine code at runtime.

11. JIT Vs JVM

JVM interprets bytecode into machine-specific instructions.
JIT compiles frequently executed bytecode into native code for efficiency.

12. Byte Code Vs Machine Code

Bytecode is a platform-independent intermediate code.
Machine Code is the platform-specific instructions executed by the CPU.

13. Basics of Java

Java is a high-level, object-oriented programming language that emphasizes code readability, simplicity, and maintainability. Understanding the basic syntax and constructs of Java is essential for effective programming.

14. Java Basic Syntax

Java syntax is largely influenced by C++, with a focus on simplicity and readability. Key elements include:

Classes and Methods: The basic building blocks of Java programs.
Statements: End with a semicolon (;).
Blocks: Enclosed in curly braces {}.
Comments: Single-line (//) and multi-line (/*...*/).

15. First Java Program (Hello World)

A basic Java program that outputs “Hello, World!” to the console is used to verify that the Java environment is set up correctly.

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Explanation:

public class HelloWorld: Defines a public class named HelloWorld.
public static void main(String[] args): The main method, which is the entry point of the program.
System.out.println(): Prints text to the console.

16. Datatypes in Java

Java has two categories of datatypes:

Primitive Datatypes: Basic types such as int, float, char, and boolean.
Non-Primitive Datatypes: Also known as reference types, including String, arrays, and objects.

17. Primitive Vs Non-Primitive Datatypes

Primitive Datatypes: Include int, char, float, double, boolean, byte, short, long.
- Characteristics: Stored directly in memory, not objects, and have a fixed size.
Non-Primitive Datatypes: Include String, Arrays, Classes, Interfaces.
- Characteristics: Stored as references to objects, can be of varying size, and can contain methods.

18. Java Identifiers

Identifiers are names given to variables, methods, classes, and other elements in Java. Rules for identifiers:

Must start with a letter, underscore (_), or dollar sign ($).
Can be followed by letters, digits, underscores, or dollar signs.
Cannot be a reserved keyword.

19. Operators in Java

Java operators are symbols that perform operations on variables and values. Key operators include:

Arithmetic Operators: +, -, *, /, %
Relational Operators: ==, !=, >, <, >=, <=
Logical Operators: &&, ||, !
Unary Operators: +, -, ++, --
Assignment Operators: =, +=, -=, *=, /=, %=
Bitwise Operators: &, |, ^, ~, <<, >>, >>>

20. Java Variables

Variables are containers for storing data values. In Java, a variable must be declared with a datatype before it can be used.

Types of Variables:

Local Variables: Declared within a method or block.
Instance Variables: Declared within a class but outside any method.
Static Variables: Declared with the static keyword and shared among all instances of a class.

21. Java Keywords

Keywords are reserved words in Java that have special meaning in the language. Examples include:

class: Defines a class.
public: Access modifier.
static: Defines class-level variables and methods.
void: Specifies that a method does not return a value.

22. Scope of Variables

The scope of a variable refers to the part of the program where the variable can be accessed. Java defines scope in terms of:

Local Scope: Within a method or block.
Instance Scope: Within an object of a class.
Global Scope: Across the entire class (static variables).

23. Wrapper Classes in Java

Wrapper classes in Java are used to convert primitive types into objects. Each primitive type has a corresponding wrapper class:

Integer: For int
Double: For double
Character: For char
Boolean: For boolean

24. Input/Output in Java

Java provides various methods for handling input and output operations.

Taking Input:

Scanner Class: Used for parsing primitive types and strings.

Scanner sc = new Scanner(System.in);
int num = sc.nextInt();

BufferedReader Class: Reads text from a character-based input stream.

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String str = br.readLine();

Printing Output:

print(): Outputs text without a newline.
println(): Outputs text with a newline.

Formatted Output:

System.out.printf(): Allows formatted output.

System.out.printf("Name: %s, Age: %d", name, age);

25. Flow Control in Java

Flow control statements manage the flow of execution in Java programs.

Decision Making:

If Statement: Executes a block of code if the condition is true.
```
if (condition) {
    // code
}
```
If-Else Statement: Executes one block of code if the condition is true, another if false.
```
if (condition) {
    // code
} else {
    // code
}
```

If-Else-If Ladder: Multiple conditions checked sequentially.

if (condition1) {
    // code
} else if (condition2) {
    // code
} else {
    // code
}

Loops:

For Loop: Iterates a block of code a specified number of times.
```
for (int i = 0; i < 10; i++) {
    // code
}
```
While Loop: Iterates as long as a condition is true.
```
while (condition) {
    // code
}
```
Do-While Loop: Executes the block of code at least once before checking the condition.
```
do {
    // code
} while (condition);
```

For Each Loop: Iterates over collections or arrays.

for (Type item : collection) {
    // code
}

Continue and Break Statements:

Continue Statement: Skips the current iteration and proceeds with the next iteration.
```
continue;
```
Break Statement: Exits from the current loop or switch statement.
```
break;
```

26. Arrays in Java

Arrays are used to store multiple values of the same type in a single variable.

Introduction:

Declaration and Initialization:
```
int[] arr = new int[5];
arr[0] = 10;
```

Multi-Dimensional Arrays:

2D Arrays:
```
int[][] matrix = new int[3][3];
```

Jagged Arrays:

Arrays of arrays where each row can have different lengths.

int[][] jaggedArray = new int[3][];
jaggedArray[0] = new int[2];
jaggedArray[1] = new int[3];

Final Arrays:

An array declared with the final keyword cannot be resized.
```
final int[] arr = {1, 2, 3};
```

Reflect Arrays:

java.util.Arrays Class: Provides utility methods for array operations.
```
Arrays.sort(arr);
```

27. Strings in Java

Strings in Java are objects that represent sequences of characters.

Introduction:

String Class: Provides various methods to manipulate strings.
```
String str = "Hello";
```

Why Strings Are Immutable:

Strings cannot be changed once created. Modifications create new String objects.

StringBuffer and StringBuilder:

StringBuffer: Mutable, thread-safe.
StringBuilder: Mutable, not thread-safe.

StringTokenizer and StringJoiner:

StringTokenizer: Used to break strings into tokens.

StringTokenizer st = new StringTokenizer("Hello World");

StringJoiner: Allows joining strings with a delimiter.

StringJoiner sj = new StringJoiner(", ");
sj.add("Hello").add("World");

28. OOPS in Java

Object-Oriented Programming (OOP) principles include encapsulation, inheritance, polymorphism, and abstraction.

Concepts:

Classes and Objects: Blueprints for creating objects and defining their properties and behaviors.
Inheritance: Mechanism where one class inherits the attributes and methods of

another class.

Polymorphism: Ability to perform a single action in different forms.
Encapsulation: Bundling of data and methods into a single unit (class).
Abstraction: Hiding the complex implementation details and showing only the necessary features.

29. Classes in Java

A class is a blueprint from which individual objects are created.

Syntax:

public class MyClass {
    // Fields
    int x;
    
    // Methods
    void display() {
        System.out.println(x);
    }
}

Creating Objects:

MyClass obj = new MyClass();
obj.x = 10;
obj.display();

30. Interfaces in Java

Interfaces define a contract that classes must follow. They can have abstract methods and default methods.

Syntax:

public interface MyInterface {
    void method1();
    default void method2() {
        System.out.println("Default method");
    }
}

Implementing Interfaces:

public class MyClass implements MyInterface {
    @Override
    public void method1() {
        System.out.println("Method1 implementation");
    }
}

31. Methods in Java

Methods are blocks of code that perform a specific task. They can return values or be void.

Syntax:

public returnType methodName(parameters) {
    // body
}

Method Overloading:

Multiple methods with the same name but different parameters.

public void display(int num) {}
public void display(String str) {}

Method Overriding:

Subclass provides a specific implementation of a method that is already defined in its superclass.
```
@Override
public void methodName() {
    // implementation
}
```

32. Packages in Java

Packages group related classes and interfaces together.

Creating a Package:

package com.example;
public class MyClass {}

Importing a Package:

import com.example.MyClass;

33. Collection Framework in Java

The Collection Framework provides a set of classes and interfaces for storing and manipulating groups of objects.

Core Interfaces:

List: Ordered collection, e.g., ArrayList, LinkedList.
Set: Collection with no duplicates, e.g., HashSet, TreeSet.
Map: Collection of key-value pairs, e.g., HashMap, TreeMap.

Iterating Through Collections:

for (String item : collection) {
    // process item
}

34. Memory Allocation in Java

Java manages memory through the JVM using heap and stack memory.

Heap Memory:

Used for dynamic memory allocation of objects and arrays.

Stack Memory:

Used for method calls and local variables.

Garbage Collection:

Automatic process of reclaiming memory by destroying objects that are no longer in use.

35. Exception Handling in Java

Exception handling in Java allows programs to handle runtime errors and maintain normal program flow.

Try-Catch Block:

try {
    // code that may throw an exception
} catch (ExceptionType e) {
    // code to handle the exception
}

Finally Block:

Executes regardless of whether an exception was thrown or not.

finally {
    // code that will always execute
}

Custom Exceptions:

Create your own exception by extending Exception class.

public class MyException extends Exception {
    public MyException(String message) {
        super(message);
    }
}

36. Multithreading in Java

Multithreading allows concurrent execution of two or more threads for better resource utilization.

Creating Threads:

Extending Thread Class:

public class MyThread extends Thread {
    public void run() {
        // code to be executed by thread
    }
}

Implementing Runnable Interface:

public class MyRunnable implements Runnable {
    public void run() {
        // code to be executed by thread
    }
}

Managing Threads:

Thread Lifecycle: New, Runnable, Blocked, Waiting, Timed Waiting, and Terminated.
Thread Methods: start(), sleep(), join(), yield().

37. Synchronization in Java

Synchronization ensures that only one thread accesses a resource at a time to avoid inconsistencies.

Synchronized Methods:

public synchronized void myMethod() {
    // synchronized code
}

Synchronized Blocks:

public void myMethod() {
    synchronized (lockObject) {
        // synchronized code
    }
}

38. File Handling in Java

Java provides classes and methods for reading from and writing to files.

File Reading:

FileReader Class:

FileReader fr = new FileReader("file.txt");
int ch;
while ((ch = fr.read()) != -1) {
    System.out.print((char) ch);
}
fr.close();

BufferedReader Class:

BufferedReader br = new BufferedReader(new FileReader("file.txt"));
String line;
while ((line = br.readLine()) != null) {
    System.out.println(line);
}
br.close();

File Writing:

FileWriter Class:

FileWriter fw = new FileWriter("file.txt");
fw.write("Hello, World!");
fw.close();

39. Java Regex

Regular expressions (Regex) are used for pattern matching and text manipulation.

Basic Patterns:

^: Start of a string.
$: End of a string.
.: Any character.
*: Zero or more occurrences.
+: One or more occurrences.

Example:

import java.util.regex.*;
Pattern p = Pattern.compile("^[a-zA-Z0-9_]*$");
Matcher m = p.matcher("valid_input123");
if (m.matches()) {
    System.out.println("Valid Input");
}

40. Java IO

Java IO (Input/Output) is a library used for handling input and output operations.

Key Classes:

File: Represents a file or directory.
FileInputStream and FileOutputStream: For reading and writing bytes.
FileReader and FileWriter: For reading and writing characters.

Example:

File file = new File("example.txt");
FileWriter writer = new FileWriter(file);
writer.write("Hello, Java IO!");
writer.close();

41. Java Networking

Java provides libraries for network communication, such as sockets and URLs.

Sockets:

Client-Side:

Socket socket = new Socket("localhost", 8080);
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
out.println("Hello Server!");
socket.close();

Server-Side:

ServerSocket serverSocket = new ServerSocket(8080);
Socket clientSocket = serverSocket.accept();
BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
System.out.println(in.readLine());
serverSocket.close();

URL Handling:

URL url = new URL("http://www.example.com");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
String inputLine;
while ((inputLine = in.readLine()) != null) {
    System.out.println(inputLine);
}
in.close();

42. Java SE 8 Features

Java SE 8 introduced several new features enhancing the language.

Key Features:

Lambda Expressions: Provide a clear and concise way to represent one method interface using an expression.
```
(a, b) -> a + b
```

Streams API: Allows functional-style operations on collections.

List<String> list = Arrays.asList("a1", "a2", "b1", "c2");
list.stream().filter(s -> s.startsWith("c")).forEach(System.out::println);

Default Methods: Methods in interfaces with default implementations.

interface MyInterface {
    default void myMethod() {
        System.out.println("Default Method");
    }
}

43. Java Date & Time

Java provides classes to handle date and time operations.

Key Classes:

LocalDate: Represents a date without time.
```
LocalDate date = LocalDate.now();
```
LocalTime: Represents a time without date.
```
LocalTime time = LocalTime.now();
```

LocalDateTime: Represents both date and time.

LocalDateTime dateTime = LocalDateTime.now();

DateTimeFormatter: Formats and parses date and time.

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String formattedDateTime = dateTime.format(formatter);

44. Java JDBC

Java Database Connectivity (JDBC) provides methods to interact with databases.

Basic Operations:

**Establish

ing a Connection**:

Connection connection = DriverManager.getConnection("jdbc:mysql://localhost/dbname", "user", "password");

Executing Queries:

Statement stmt = connection.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM users");
while (rs.next()) {
    System.out.println(rs.getString("username"));
}

Closing Connections:

rs.close();
stmt.close();
connection.close();

45. Java Reflection

Java Reflection provides a way to inspect and manipulate classes and objects at runtime.

Example:

Inspecting Class Information:

Class<?> clazz = Class.forName("java.util.ArrayList");
System.out.println("Class Name: " + clazz.getName());

Creating Instances Dynamically:
```
Object obj = clazz.newInstance();
```

46. Java Annotations

Annotations provide metadata about code and can be used for various purposes such as code analysis, documentation, and runtime processing.

Defining Annotations:

public @interface MyAnnotation {
    String value();
}

Using Annotations:

@MyAnnotation(value = "example")
public class MyClass {}

Accessing Annotations:

MyAnnotation annotation = MyClass.class.getAnnotation(MyAnnotation.class);
System.out.println(annotation.value());

47. Java Generics

Generics enable you to define classes, interfaces, and methods with type parameters.

Syntax:

Generic Class:

public class MyGenericClass<T> {
    private T value;
    public void setValue(T value) {
        this.value = value;
    }
    public T getValue() {
        return value;
    }
}

Using Generics:

MyGenericClass<String> stringInstance = new MyGenericClass<>();
stringInstance.setValue("Hello");
System.out.println(stringInstance.getValue());

48. Java Enums

Enums represent a fixed set of constants. They are useful for defining a collection of related values.

Syntax:

public enum Day {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY
}

Using Enums:

Day today = Day.MONDAY;
if (today == Day.MONDAY) {
    System.out.println("Start of the work week");
}

49. Java Swing

Swing is a GUI toolkit for Java that provides a set of ‘lightweight’ (all-Java language) components.

Creating a Simple Window:

import javax.swing.JFrame;
import javax.swing.JButton;

public class MySwingApp {
    public static void main(String[] args) {
        JFrame frame = new JFrame("My Swing App");
        JButton button = new JButton("Click Me");
        frame.add(button);
        frame.setSize(300, 200);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

50. JavaFX

JavaFX is another GUI framework for creating modern desktop applications.

Basic Example:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class MyJavaFXApp extends Application {
    @Override
    public void start(Stage primaryStage) {
        Button btn = new Button("Click Me");
        StackPane root = new StackPane();
        root.getChildren().add(btn);
        Scene scene = new Scene(root, 300, 250);
        primaryStage.setTitle("JavaFX Application");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

Here’s an in-depth explanation of each topic related to Java, designed to provide a comprehensive understanding for exam preparation.

1. Introduction to Java

Overview

Java is a high-level, class-based, object-oriented programming language designed to have as few implementation dependencies as possible. It was developed by Sun Microsystems in 1995 and is now owned by Oracle Corporation.

Key Features

Platform Independence: Java programs are compiled into bytecode, which can be executed on any platform with a Java Virtual Machine (JVM).
Object-Oriented: Java is designed around the concept of objects and classes.
Simple and Familiar: Java’s syntax is similar to C++ but simpler, with fewer low-level programming constructs.
Secure: Java provides a secure execution environment through its robust security model.
Robust: Java emphasizes early error checking and runtime checking.

2. Java Setup

How to Download and Install Java

Download: Visit the Oracle Java SE Downloads page and download the appropriate JDK version for your operating system.
Install: Run the installer and follow the installation wizard.
Set Up Environment Variables:
- On Windows: Set JAVA_HOME to the JDK installation path and update the PATH variable to include JAVA_HOME/bin.
- On macOS/Linux: Update .bash_profile or .bashrc with export JAVA_HOME=/path/to/jdk and export PATH=$JAVA_HOME/bin:$PATH.

Verify Installation

Run java -version and javac -version in the terminal or command prompt to verify that Java is installed correctly.

3. Basic Syntax

Structure of a Java Program

Class Declaration: Every Java application must have at least one class.
Main Method: The entry point for any Java application is the main method: public static void main(String[] args).

Syntax Rules

Statements: End with a semicolon (;).
Blocks: Enclosed in curly braces ({}).
Indentation: Not required but recommended for readability.

4. Data Types

Primitive Data Types

byte: 8-bit integer, range from -128 to 127.
short: 16-bit integer, range from -32,768 to 32,767.
int: 32-bit integer, range from -2^31 to 2^31-1.
long: 64-bit integer, range from -2^63 to 2^63-1.
float: Single-precision 32-bit IEEE 754 floating point.
double: Double-precision 64-bit IEEE 754 floating point.
char: 16-bit Unicode character.
boolean: Represents true or false.

Non-Primitive Data Types

Strings: Sequence of characters.
Arrays: Collection of elements of the same type.
Classes: Blueprints for objects.

5. Variables

Declaration and Initialization

Syntax: <data_type> <variable_name> = <value>;
Example: int age = 25;

Variable Scope

Local Variables: Declared inside methods or blocks.
Instance Variables: Declared inside a class but outside methods.
Static Variables: Declared with the static keyword; shared among all instances of a class.

6. Operators

Arithmetic Operators

Examples: +, -, *, /, %

Relational Operators

Examples: ==, !=, >, <, >=, <=

Logical Operators

Examples: &&, ||, !

Bitwise Operators

Examples: &, |, ^, ~, <<, >>, >>>

Unary Operators

Examples: +, -, ++, --, !

Assignment Operators

Examples: =, +=, -=, *=, /=, %=

Ternary Operator

Syntax: <condition> ? <true_value> : <false_value>;

7. Control Statements

Decision Making

If Statement: Executes a block of code if a condition is true.
If-Else Statement: Executes one block if the condition is true and another if false.
Switch Statement: Allows multi-way branching based on the value of an expression.

Loops

For Loop: Iterates a block of code a specified number of times.
While Loop: Repeats a block of code while a condition is true.
Do-While Loop: Similar to while, but guarantees at least one execution of the loop.

Control Flow

Break Statement: Exits from the nearest loop or switch statement.
Continue Statement: Skips the current iteration of a loop and proceeds to the next iteration.

8. Arrays

Single-Dimensional Arrays

Declaration: int[] arrayName;
Initialization: arrayName = new int[10];

Multi-Dimensional Arrays

Declaration: int[][] arrayName;
Initialization: arrayName = new int[3][4];

Jagged Arrays

Declaration: int[][] jaggedArray = new int[3][];
Initialization: jaggedArray[0] = new int[2];

Array Operations

Traversing: Use loops to access elements.
Manipulation: Sorting, searching, etc.

9. Strings

String Class

Immutable: Once created, the contents of a string cannot be changed.
Common Methods: length(), charAt(), substring(), indexOf(), concat()

StringBuffer and StringBuilder

StringBuffer: Mutable, thread-safe.
StringBuilder: Mutable, not thread-safe, generally faster than StringBuffer.

String Manipulation

Concatenation: Using + operator or concat() method.
Comparison: Using equals() and compareTo() methods.

10. OOPS Concepts

Classes and Objects

Class: Blueprint for objects. Contains fields and methods.
Object: Instance of a class.

Inheritance

Concept: Mechanism where one class inherits the fields and methods of another.
Syntax: class Child extends Parent { }

Polymorphism

Concept: Ability of a class to provide different implementations of methods based on the object.
Types: Compile-time (method overloading) and runtime (method overriding).

Encapsulation

Concept: Bundling the data (variables) and methods that operate on the data into a single unit (class).
Access Modifiers: private, protected, public

Abstraction

Concept: Hiding implementation details and showing only functionality to the user.
Abstract Classes and Interfaces: Used to achieve abstraction.

11. Interfaces

Definition

Concept: A reference type in Java that can contain only constants, method signatures, default methods, static methods, and nested types.
Syntax: interface InterfaceName { }

Functional Interface

Definition: An interface with exactly one abstract method.
Example: @FunctionalInterface annotation.

Marker Interface

Definition: An interface with no methods or fields, used to provide metadata to the JVM.

Comparator vs. Comparable

Comparable: Used to define a natural ordering of objects.
Comparator: Used to define custom ordering.

12. Methods

Method Declaration

Syntax: return_type methodName(parameters) { }

Method Overloading

Concept: Multiple methods with the same name but different parameters.

Method Overriding

Concept: Redefining a method in a subclass that is already defined in the parent class.

Static vs. Instance Methods

Static Methods: Belong to the class, not instances.
Instance Methods: Belong to individual instances of a class.

13. Packages

Definition

Concept: Namespace for organizing classes and interfaces.

Creating a Package

Syntax: package packageName;

Importing Packages

Syntax: import packageName.ClassName; or import packageName.*;

Common Packages

java.util: Contains utility classes like ArrayList, HashMap.
java.lang: Provides fundamental classes like String, Math.
java.io: Handles input and output operations.

14. Collection Framework

Interfaces and Classes

Collection Interface: Root interface for all collections.
List Interface: Ordered collection (e.g., ArrayList, `Linked

List`).

Set Interface: Unordered collection (e.g., HashSet, TreeSet).
Map Interface: Collection of key-value pairs (e.g., HashMap, TreeMap).

Common Operations

Adding Elements: add(), put()
Removing Elements: remove()
Iterating: Using iterators or enhanced for-loops.

15. Memory Management

Heap vs. Stack

Heap: Memory for object storage, managed by the garbage collector.
Stack: Memory for method calls and local variables.

Garbage Collection

Concept: Automatic memory management that reclaims memory used by objects no longer referenced.
Types: Mark-and-sweep, generational garbage collection.

Memory Leaks

Definition: When objects are not properly garbage collected due to lingering references.

16. Exception Handling

Types of Exceptions

Checked Exceptions: Must be declared in the method signature or handled (e.g., IOException).
Unchecked Exceptions: Runtime exceptions that do not need to be declared or caught (e.g., NullPointerException).

Try-Catch-Finally

Try Block: Contains code that might throw an exception.
Catch Block: Handles the exception.
Finally Block: Executes code regardless of whether an exception was thrown.

Throw vs. Throws

Throw: Used to explicitly throw an exception.
Throws: Used in method signatures to declare that a method can throw an exception.

17. Multithreading

Thread Creation

Using Thread Class: Extend Thread and override run().
Using Runnable Interface: Implement Runnable and pass it to a Thread object.

Thread Lifecycle

States: New, Runnable, Blocked, Waiting, Timed Waiting, Terminated.

Synchronization

Concept: Ensuring that multiple threads do not interfere with each other while accessing shared resources.
Keywords: synchronized, volatile

Concurrency Utilities

ExecutorService: For managing thread pools.
Future: For handling asynchronous tasks.

18. File Handling

File Operations

Reading Files: Using FileReader, BufferedReader.
Writing Files: Using FileWriter, BufferedWriter.

File Class

Concept: Represents a file or directory path.

Exception Handling

FileNotFoundException: Occurs when trying to access a file that does not exist.
IOException: General input/output exception.

19. Regular Expressions

Syntax and Usage

Pattern Matching: Using Pattern and Matcher classes.
Common Patterns: \d for digits, \w for word characters, . for any character.

Methods

Pattern.compile(): Compiles the regex into a pattern.
Matcher.find(): Finds matches in the input string.

20. Java Networking

Socket Programming

Client-Server Model: Establish connections between client and server.
Socket Class: For client-side connections.
ServerSocket Class: For server-side connections.

Protocols

TCP: Reliable, connection-oriented.
UDP: Connectionless, faster but less reliable.

21. Java SE 8 Features

Lambda Expressions

Concept: Anonymous function that can be passed around as a parameter.
Syntax: (parameters) -> expression

Streams API

Concept: Provides a high-level abstraction for processing sequences of elements.
Common Operations: filter(), map(), reduce()

Date and Time API

Classes: LocalDate, LocalTime, LocalDateTime

22. Java Date & Time

Old Date and Time Classes

Date: Represents date and time but is mutable.
Calendar: Abstract class for date and time manipulation.

New Date and Time API (Java 8+)

LocalDate: Immutable class for dates.
LocalTime: Immutable class for time.
LocalDateTime: Combines date and time.

23. JDBC (Java Database Connectivity)

Overview

Concept: API for connecting and executing queries on a database.

JDBC Components

DriverManager: Manages a list of database drivers.
Connection: Interface for database connection.
Statement: Interface for executing SQL queries.
ResultSet: Represents the result set of a query.

Common Operations

Connecting: DriverManager.getConnection()
Executing Queries: Using Statement or PreparedStatement.

24. Java Miscellaneous

Reflection

Concept: Allows inspection and manipulation of classes, methods, and fields at runtime.

JavaFX

Concept: Framework for building rich graphical user interfaces.

RMI (Remote Method Invocation)

Concept: Allows objects to invoke methods on an object located in another JVM.

Java Study Resources: Books, Websites, and Tools for Deep Learning

Here’s a streamlined list of resources for study purposes:

1. Introduction to Java

Oracle Java Tutorials: Java Tutorials
Java Programming and Software Engineering Fundamentals (Coursera): Coursera Specialization

2. Java Setup

Oracle JDK Installation Guide: Installation Guide
GeeksforGeeks Setup Guide: GeeksforGeeks Setup

3. Basic Syntax

Java Basics on W3Schools: W3Schools Java Syntax
Java Basic Syntax (TutorialsPoint): TutorialsPoint Basics

4. Data Types

GeeksforGeeks Data Types: Data Types Overview
Java Primitive Data Types (JavatPoint): Primitive Types

5. Variables

Java Variables on W3Schools: Java Variables
Java Variables and Data Types (TutorialsPoint): Variables Overview

6. Operators

Java Operators on W3Schools: Java Operators
Java Operators Guide (TutorialsPoint): Operators Guide

7. Arrays

Java Arrays on GeeksforGeeks: Arrays Overview
Java 2D Arrays (JavatPoint): 2D Arrays

8. Strings

Java Strings on W3Schools: Java Strings
String Immutability (JavatPoint): Why Strings Are Immutable

9. OOPS in Java

Object-Oriented Programming Concepts: GeeksforGeeks OOP
Java OOPS Concepts (TutorialsPoint): OOPS in Java

10. Exception Handling

Java Exception Handling (Oracle): Exception Handling Overview
Java Exceptions and Error Handling (GeeksforGeeks): Exception Handling Guide

11. Multithreading

Java Multithreading Tutorial (GeeksforGeeks): Multithreading Overview
Java Multithreading Guide (TutorialsPoint): Multithreading Guide

12. File Handling

Java File Handling Basics (W3Schools): File Handling
Java File I/O (TutorialsPoint): File I/O Guide

13. Networking

Java Networking Tutorial (Oracle): Networking Overview
Java Networking Guide (GeeksforGeeks): Networking Basics

14. Java 8 Features

Java 8 New Features (Oracle): Java SE 8 Features
Java 8 Features Overview (GeeksforGeeks): Java 8 Features

15. JDBC

Java JDBC Tutorial (Oracle): JDBC Tutorial
JDBC Basics (TutorialsPoint): JDBC Guide

Overview of Java

Table of Contents

1. Introduction to Java

2. History of Java

3. Java vs C++ vs Python

4. How to Download and Install Java?

5. Setting Up the Environment in Java

6. How to Download and Install Eclipse on Windows?

7. Java Development Kit (JDK)

8. JVM and Its Architecture

JVM Components:

9. JDK Vs JRE Vs JVM

10. Just In Time Compiler

11. JIT Vs JVM

12. Byte Code Vs Machine Code

13. Basics of Java

14. Java Basic Syntax

15. First Java Program (Hello World)

Explanation:

16. Datatypes in Java

17. Primitive Vs Non-Primitive Datatypes

18. Java Identifiers

19. Operators in Java

20. Java Variables

Types of Variables:

21. Java Keywords

22. Scope of Variables

23. Wrapper Classes in Java

24. Input/Output in Java

Taking Input:

Printing Output:

Formatted Output:

25. Flow Control in Java

Decision Making:

Loops:

Continue and Break Statements:

26. Arrays in Java

Introduction:

Multi-Dimensional Arrays:

Jagged Arrays:

Final Arrays:

Reflect Arrays:

27. Strings in Java

Introduction:

Why Strings Are Immutable:

StringBuffer and StringBuilder:

StringTokenizer and StringJoiner:

28. OOPS in Java

Concepts:

29. Classes in Java

Syntax:

Creating Objects:

30. Interfaces in Java

Syntax:

Implementing Interfaces:

31. Methods in Java

Syntax:

Method Overloading:

Method Overriding:

32. Packages in Java

Creating a Package:

Importing a Package:

33. Collection Framework in Java

Core Interfaces:

Iterating Through Collections:

34. Memory Allocation in Java

Heap Memory:

Stack Memory:

Garbage Collection:

35. Exception Handling in Java

Try-Catch Block:

Finally Block:

Custom Exceptions:

36. Multithreading in Java

Creating Threads:

Managing Threads:

37. Synchronization in Java

Synchronized Methods:

Synchronized Blocks:

38. File Handling in Java