Day 1: Core Java Fundamentals & Collections Framework

Goal:

Refresh foundational knowledge of Java.
Understand the Collections Framework deeply.

Study Time: 5-6 hours (with breaks)

1. Java Language Features Refresher (1-1.5 hours)

Objective: Revisit important Java features that are fundamental for problem-solving and coding challenges.

Topics:

Primitive Types & Wrappers: Difference between primitive and wrapper classes, autoboxing/unboxing.
Control Structures: Loops (for, while), conditionals (if-else, switch), and iteration.
Memory Management: Stack vs. Heap, Garbage Collection.
String Handling: Immutability of Strings, StringBuilder vs. StringBuffer.

Tasks:

Reading: Go through documentation or a trusted source like Effective Java or the official Oracle Java tutorials on these topics.
Code Exercise: Write small programs to refresh your understanding.
- Example: Write a program that reverses a string using StringBuilder.
- Example: Implement basic arithmetic using primitive types, demonstrate autoboxing.

Practice:

HackerRank - Java Introduction Problems
Write a program that uses both for and while loops to iterate through a list of numbers, printing only the odd ones.

2. Collections Framework Overview (2-2.5 hours)

Objective: Deeply understand the Java Collections Framework, which is crucial for interviews. Collections provide data structures such as lists, sets, and maps, which are frequently used in coding problems.

Topics:

Collection Interfaces Overview:
- List, Set, Queue, Map.
Key Implementations:
- ArrayList, LinkedList, HashSet, TreeSet, HashMap, LinkedHashMap, TreeMap, PriorityQueue.
Common Methods & Performance:
- Add, remove, search (get(), put()), iteration, time complexity of operations.
- How different implementations handle data (e.g., HashMap vs. TreeMap).
Internal Working of Collections:
- How HashMap works (hashing, bucket storage, rehashing).
- Differences between ArrayList and LinkedList.

Tasks:

Reading: Refer to the official Java Collections documentation and read about:
- Internal working of HashMap.
- Differences between Set and List.
Hands-On Code Exercise:
- Create an ArrayList, HashSet, and HashMap, and perform basic operations like adding, removing, and iterating.
- Example 1: Write a Java program to count the frequency of characters in a string using HashMap.
- Example 2: Implement a small program using PriorityQueue to simulate a job scheduler.

Practice:

3. Understanding Generics in Java (1-1.5 hours)

Objective: Learn how to use generics with collections. This is a crucial topic as many data structures use generics for type safety.

Topics:

Generic Classes and Methods:
- How to define and use generics in Java.
- Type safety and how it eliminates ClassCastException.
Bounded Type Parameters:
- <? extends T> and <? super T> — What they mean and when to use them.

Tasks:

Reading: Go through a tutorial on Java Generics (Oracle documentation or any trusted guide).
Hands-On Code Exercise:
- Write a generic class to demonstrate the use of generics.
- Example: Create a class Box<T> that can store any type and provide methods to access it.

Practice:

Write a program to demonstrate the difference between ? extends T and ? super T using a simple example like a collection of numbers.

4. Summary & Review (30 minutes)

Objective: Wrap up the day's learning by reviewing key points and ensuring you understand the concepts.

Tasks:

Revisit the key concepts learned:
- Collections Framework, key differences between data structures.
- Core Java features and syntax.
- Importance of Generics and how they improve type safety.
Review the code you've written during the day, make sure you understand each line of code.

Reflective Questions:

What’s the internal working of HashMap? Why is HashSet faster than TreeSet for most operations?
How does ArrayList grow dynamically? What’s the cost of resizing?
How can you use Generics to write flexible code?

5. Mock Interview or Practice Problem Solving (Optional, 1 hour)

Objective: Solve 1-2 medium-level coding problems related to the topics covered today to simulate an interview.

Additional Resources:

Books:
- Effective Java by Joshua Bloch (for advanced concepts and best practices).
- Java: The Complete Reference by Herbert Schildt.
Online Courses:
- Java Collections Framework - Pluralsight
- Generics in Java - Baeldung