🧩 Week 2 – Assignment

Student Management System (Collections + Exceptions Integration)

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🎯 Objective

Enhance your existing Student Management System (created in Week 1) by:

• Using appropriate Collections
• Preventing duplicates
• Using Map for efficient lookup
• Applying Streams for filtering
• Implementing custom exceptions
• Handling errors properly

This assignment simulates real backend service-layer logic.

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📌 Problem Statement

You are building a basic in-memory backend system for managing students.

You must design a StudentService class that performs operations on students using proper data structures and exception handling.

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🏗 Requirements

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1️⃣ Student Class

Create a Student class with:

• int id
• String name
• int marks

Constraints:

• id must be unique
• marks must be between 0 and 100

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2️⃣ Data Storage Strategy (Important)

Inside StudentService, use:

• List<Student> → to store all students
• Map<Integer, Student> → for fast lookup by id
• Set<Integer> → to ensure unique IDs

⚠️ You must justify in comments why you are using each collection.

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🧠 Functional Requirements

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1️⃣ Add Student

Method:

addStudent(Student student)

Rules:

• If ID already exists → throw DuplicateStudentException
• If marks < 0 or > 100 → throw InvalidMarksException

• Otherwise:

  • Add to List
  • Add ID to Set
  • Add to Map

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2️⃣ Get Student by ID

Method:

getStudentById(int id)

Rules:

• If student not found → throw StudentNotFoundException

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3️⃣ Remove Student

Method:

removeStudent(int id)

Rules:

• If not found → throw exception

• Remove from:

  • List
  • Map
  • Set

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4️⃣ Get All Students

Return all students as List.

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5️⃣ Get Top Scorers

Method:

getTopScorers(int threshold)

Requirements:

• Use Stream API
• Return students with marks > threshold
• Sort descending by marks

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6️⃣ Get Average Marks

Method:

getAverageMarks()

Use Streams.

If no students exist:

• Throw custom exception OR return 0 (justify decision).

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🚨 Custom Exceptions (Mandatory)

Create:

• DuplicateStudentException
• StudentNotFoundException
• InvalidMarksException

All should extend RuntimeException.

Each must:

• Accept meaningful message
• Be used appropriately

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🔎 Exception Handling

In your main() method:

• Wrap calls inside try-catch
• Print meaningful error messages
• Do NOT swallow exceptions silently

Example pattern:

try {
    service.addStudent(student);
} catch (DuplicateStudentException e) {
    System.out.println(e.getMessage());
}

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📊 Edge Case Handling

You must handle:

• Adding duplicate ID
• Removing non-existing student
• Getting student from empty list
• Filtering when no students match
• Null student input (optional advanced)

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🧪 Manual Testing Required

In main():

1. Add 5 students
2. Attempt duplicate insert
3. Attempt invalid marks
4. Retrieve existing student
5. Retrieve non-existing student
6. Print top scorers
7. Remove student
8. Print final list

Document your test scenarios in comments.

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🏆 Evaluation Criteria

Criteria	Weight
Correct collection usage	20%
Proper exception handling	20%
Stream usage	15%
Clean code structure	15%
Edge case handling	15%
Code readability	15%

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📁 Expected Structure

Student.java
StudentService.java
DuplicateStudentException.java
InvalidMarksException.java
StudentNotFoundException.java
Main.java

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🧠 Design Thinking Questions (To Be Answered in Comments)

Answer these in comments inside your code:

1. Why use Map in addition to List?
2. Why not use only List?
3. Why is Set used?
4. Why are custom exceptions better than returning null?
5. Why use Stream instead of loop for filtering?

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🚀 Bonus (Optional)

If you want to go further:

• Use Optional<Student> in some method
• Add logging instead of System.out
• Write a basic unit test
• Make Student immutable
• Use Comparator separately

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🎯 Learning Outcome

After completing this assignment, you should be able to:

✔ Choose correct collection types ✔ Understand hashing behavior ✔ Design service-layer logic ✔ Throw meaningful domain exceptions ✔ Use Streams in real scenario ✔ Think like backend engineer

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🔥 Mentor Note (For Review Session)

During review, you should be able to:

• Explain your data structure choices
• Explain exception design
• Walk through one method confidently
• Handle edge case questions

This assignment is not about syntax. It is about backend reasoning.

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