First Move (11~18) - Code, Learn, Build
🧭 Career CompassDashboardProgress
Loading...
First Move (11~18) - Code, Learn, Build

Structured, level-based technology learning paths from foundational exploration to industry mastery.

Learning Domains

  • Python Programming (Active)
  • Computer Science Core
  • Web Development
  • AI & Machine Learning

Platform Architecture

  • Level-Based Progression
  • Decoupled Content Schema
  • Modular Code Execution Engine
  • Curated Official Resources

© 2026 First Move (11~18) • CODE • LEARN • BUILD. Built with Next.js App Router.

Readability & Accessibility First

← Java Enterprise Development|Level 2: Collections, Memory Management & Advanced Java Features

9. Java Generics, Type Erasure, Wildcards & Covariance/Contravariance

Lesson 9 of 25
Saved Locally (Guest)
Progress
0%

Java Generics, Type Erasure, Wildcards & Covariance/Contravariance

Master generic classes, generic methods, compile-time Type Erasure mechanics, wildcards (`?`), bounded wildcards (`? extends T` vs `? super T`), and PECS principle.

Type Erasure & The PECS Principle

### The PECS Rule (Producer Extends, Consumer Super) - **Producer Extends (`? extends T`)**: Use when your generic parameter ONLY provides data (read-only). - **Consumer Super (`? super T`)**: Use when your generic parameter ONLY consumes data (write-only). - **Type Erasure**: Java compiler removes all generic type information during compilation, replacing parameters with Object or bound types for backward compatibility with pre-Java 5 bytecodes!
💻 Ready to test your knowledge with code?
Solve the hands-on coding exercise in the interactive code editor.