✅ 1. OOP Concepts (1-minute memory)

• Encapsulation → wrap data + methods → private fields, getters/setters
• Inheritance → parent → child
• Polymorphism
  • Overload = same name, diff params
  • Override = child replaces parent method
• Abstraction → hide complexity → interfaces + abstract classes

✅ 2. Java Keywords

• final → cannot change
• static → belongs to class
• this → current object
• super → parent reference

✅ 3. String Notes

• String immutable
• StringBuilder → fast, non-thread-safe
• StringBuffer → thread-safe, slow

✅ 4. Collections Cheatsheet

List

• ArrayList → fast read