Java Programming - Lecture 38

Java Programming

Lecture 38: Generics in Java

GTU Diploma in Computer Engineering

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Learning Objectives

After this lecture, you will be able to:

  • Understand the concept and benefits of Generics in Java
  • Create generic classes, interfaces, and methods
  • Work with bounded type parameters and wildcards
  • Implement type erasure concepts
  • Use generic collections effectively
  • Apply generic programming best practices

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Lecture Overview

  1. Introduction to Generics
  2. Generic Classes and Interfaces
  3. Generic Methods
  4. Bounded Type Parameters
  5. Wildcards in Generics
  6. Type Erasure
  7. Generic Collections
  8. Best Practices
  9. Hands-on Exercises

What are Generics?

Generics enable type safety at compile time and eliminate the need for casting.

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Benefits of Generics

  1. Type Safety: Compile-time type checking
  2. Elimination of Casting: No explicit casting needed
  3. Code Clarity: Code is more readable and self-documenting
  4. Performance: No boxing/unboxing overhead

Generic Classes

Generic classes allow you to create classes that work with different types.

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Multiple Type Parameters

Classes can have multiple generic type parameters.

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Generic Interfaces

Interfaces can also be generic.

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Generic Methods

Methods can be generic independently of their class.

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Generic Method Usage

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Bounded Type Parameters

You can restrict the types that can be used as type arguments.

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Multiple Bounds

A type parameter can have multiple bounds.

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Wildcards in Generics

Wildcards represent unknown types in generics.

Unbounded Wildcard (?)

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Upper Bounded Wildcards

Use ? extends Type for reading from a generic collection.

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Lower Bounded Wildcards

Use ? super Type for writing to a generic collection.

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PECS Principle

Producer Extends, Consumer Super - A guideline for using wildcards.

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Type Erasure

Java implements generics through type erasure - generic type information is removed at runtime.

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Generic Collections in Practice

Using generics with Java Collections Framework.

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Advanced Generic Collections

Working with nested generics and complex types.

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Generic Best Practices

1. Use Meaningful Type Parameter Names

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2. Favor Generic Types Over Raw Types

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More Best Practices

3. Use Bounded Wildcards for Flexibility

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4. Eliminate Unchecked Warnings

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5. Prefer Lists to Arrays for Type Safety

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Real-World Generic Example: Repository Pattern

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Repository Implementation Example

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Using the Generic Repository

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Hands-on Exercise 1: Generic Stack Implementation

Create a generic Stack class with the following requirements:

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Test your implementation with different data types.

Hands-on Exercise 2: Generic Utility Methods

Implement the following generic utility methods:

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Create test cases for each method with different data types.

Hands-on Exercise 3: Generic Cache Implementation

Create a generic LRU (Least Recently Used) cache:

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Test your cache with different key-value types and verify LRU behavior.

Exercise Solutions: Generic Stack

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Exercise Solutions: Generic Utilities

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Performance Considerations

Generic Collections Performance

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Common Generic Pitfalls

1. Generic Array Creation

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2. Static Context and Generics

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Summary

Key Concepts Covered

  1. Generic Classes and Interfaces: Type-safe containers and contracts
  2. Generic Methods: Methods that work with different types
  3. Bounded Type Parameters: Restricting generic types
  4. Wildcards: Flexible type handling with ?, extends, and super
  5. Type Erasure: Runtime behavior of generics
  6. PECS Principle: Producer Extends, Consumer Super
  7. Best Practices: Writing clean, safe generic code

Benefits of Generics

  • Type Safety: Compile-time error detection
  • Code Reusability: Same code works with different types
  • Performance: Elimination of casting overhead
  • Clarity: Self-documenting code

When to Use Generics

  • Collections and data structures
  • Utility methods that work with multiple types
  • APIs that need type safety
  • Framework and library development

Next Lecture Preview

Lecture 39: Lambda Expressions and Functional Interfaces

  • Introduction to Functional Programming in Java
  • Lambda Expression Syntax
  • Method References
  • Built-in Functional Interfaces
  • Custom Functional Interfaces
  • Functional Programming Patterns

Preparation

  • Review interfaces and anonymous classes
  • Practice with generic collections
  • Understand the concept of functions as first-class objects

Thank You!

Questions and Discussion

  • How do generics improve code safety and maintainability?
  • When would you choose wildcards over specific type parameters?
  • What are the trade-offs between generic collections and arrays?

Resources for Further Learning

  • Oracle Java Generics Tutorial
  • Effective Java by Joshua Bloch (Chapter on Generics)
  • Practice generic programming with different data structures

Next: Lambda Expressions and Functional Programming