🔍 Advanced Java Concepts (Q11–Q20)

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11. 🧩 Interface vs Abstract Class in Java

🔹 Interface

• A collection of abstract methods and static constants.
• Can include default and static methods (since Java 8).
• A class can implement multiple interfaces.

🔸 Abstract Class

• Can have both abstract and concrete methods.
• A class can extend only one abstract class.

Feature	Interface	Abstract Class
Methods	Abstract (default), static, default	Abstract + Concrete
Multiple Inheritance	Yes (via implements)	No (only single inheritance)
Constructor	Not allowed	Allowed

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12. 🔐 Access Modifiers in Java

Modifier	Scope
public	Accessible from anywhere
protected	Accessible within same package and subclasses
default	Accessible within same package only
private	Accessible within the same class only

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13. 📦 Encapsulation in Java

Encapsulation is the process of wrapping data and methods into a single unit (class).

✅ Implementation:

1. Declare variables as private.
2. Provide public getter and setter methods.

class Person {
  private String name;
  public String getName() { return name; }
  public void setName(String name) { this.name = name; }
}

14. 🗂️ Packages in Java

Packages are namespaces that group related classes and interfaces.

✅ Benefits:

• Avoids name conflicts
• Improves code organization
• Supports modular development

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15. ⚙️ Static Variables and Methods

• Static Variable: Shared across all instances of a class.
• Static Method: Belongs to the class, not instances.

class Example {
  static int count = 0;
  static void display() {
    System.out.println("Count: " + count);
  }
}

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16. 🔄 Thread Lifecycle in Java

State	Description
New	Thread is created
Runnable	Ready to run
Running	Actively executing
Blocked	Waiting for a resource
Terminated	Execution completed

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17. ⚠️ Exception Handling in Java

Java handles runtime errors using:

try {
  // risky code
} catch (Exception e) {
  // handle error
} finally {
  // cleanup code
}

Keywords:

• try, catch, throw, throws, finally

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18. 🧨 throw vs throws

Keyword	Purpose
throw	Used to explicitly throw an exception
throws	Declares exceptions a method might throw

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19. ✅ Checked vs Unchecked Exceptions

Type	Checked at	Examples
Checked	Compile-time	IOException, SQLException
Unchecked	Runtime	NullPointerException, ArithmeticException

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20. 🔒 Synchronization in Java

Synchronization ensures that only one thread accesses a critical section at a time.

synchronized void updateBalance() {
  // critical section
}

📌 What’s Next?

👉 Explore detailed answers, code samples, use cases, and illustrations in upcoming parts of this series:

• Part 1: Object-Oriented Basics & Language Features
• Part 0: All 50 Questions
• Part 3: Collections, Hashing & Generics
• Part 4: Functional APIs, Exceptions & Final Keywords
• Part 5: Advanced Concepts, Concurrency & Modularity