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)

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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.

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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:

• HackerRank - Java Collections Challenges
• LeetCode - Easy Data Structure Problems

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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.

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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?

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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.

Suggested Problems:

• Problem 1: Implement a custom ArrayList from scratch to understand the internal workings.
• Problem 2: Use a HashMap to solve a problem where you find the first non-repeating character in a string.

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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