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Abhishek Kumar
Abhishek Kumar

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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:

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.

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.

Additional Resources:

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