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Programming Scala

Cover of Programming Scala by Dean Wampler... Published by O'Reilly Media, Inc.
  1. Programming Scala
    1. SPECIAL OFFER: Upgrade this ebook with O’Reilly
    2. A Note Regarding Supplemental Files
    3. Foreword
    4. Preface
      1. Welcome to Programming Scala
      2. Conventions Used in This Book
      3. Using Code Examples
      4. Safari® Books Online
      5. How to Contact Us
      6. Acknowledgments
    5. 1. Zero to Sixty: Introducing Scala
      1. Why Scala?
      2. Installing Scala
      3. For More Information
      4. A Taste of Scala
      5. A Taste of Concurrency
      6. Recap and What’s Next
    6. 2. Type Less, Do More
      1. In This Chapter
      2. Semicolons
      3. Variable Declarations
      4. Method Declarations
      5. Inferring Type Information
      6. Literals
      7. Tuples
      8. Option, Some, and None: Avoiding nulls
      9. Organizing Code in Files and Namespaces
      10. Importing Types and Their Members
      11. Abstract Types And Parameterized Types
      12. Reserved Words
      13. Recap and What’s Next
    7. 3. Rounding Out the Essentials
      1. Operator? Operator?
      2. Methods Without Parentheses and Dots
      3. Domain-Specific Languages
      4. Scala if Statements
      5. Scala for Comprehensions
      6. Other Looping Constructs
      7. Conditional Operators
      8. Pattern Matching
      9. Enumerations
      10. Recap and What’s Next
    8. 4. Traits
      1. Introducing Traits
      2. Stackable Traits
      3. Constructing Traits
      4. Recap and What’s Next
    9. 5. Basic Object-Oriented Programming in Scala
      1. Class and Object Basics
      2. Parent Classes
      3. Constructors in Scala
      4. Nested Classes
      5. Visibility Rules
      6. Recap and What’s Next
    10. 6. Advanced Object-Oriented Programming In Scala
      1. Overriding Members of Classes and Traits
      2. Companion Objects
      3. Case Classes
      4. Equality of Objects
      5. Recap and What’s Next
    11. 7. The Scala Object System
      1. The Predef Object
      2. Classes and Objects: Where Are the Statics?
      3. Sealed Class Hierarchies
      4. The Scala Type Hierarchy
      5. Linearization of an Object’s Hierarchy
      6. Recap and What’s Next
    12. 8. Functional Programming in Scala
      1. What Is Functional Programming?
      2. Functional Programming in Scala
      3. Recursion
      4. Tail Calls and Tail-Call Optimization
      5. Functional Data Structures
      6. Traversing, Mapping, Filtering, Folding, and Reducing
      7. Pattern Matching
      8. Partial Functions
      9. Currying
      10. Implicits
      11. Implicit Function Parameters
      12. Call by Name, Call by Value
      13. Lazy Vals
      14. Recap: Functional Component Abstractions
    13. 9. Robust, Scalable Concurrency with Actors
      1. The Problems of Shared, Synchronized State
      2. Actors
      3. Actors in Scala
      4. Traditional Concurrency in Scala: Threading and Events
      5. Recap and What’s Next
    14. 10. Herding XML in Scala
      1. Reading XML
      2. Writing XML
      3. Recap and What’s Next
    15. 11. Domain-Specific Languages in Scala
      1. Internal DSLs
      2. External DSLs with Parser Combinators
      3. Recap and What’s Next
    16. 12. The Scala Type System
      1. Reflecting on Types
      2. Understanding Parameterized Types
      3. Variance Under Inheritance
      4. Type Bounds
      5. Nothing and Null
      6. Understanding Abstract Types
      7. Path-Dependent Types
      8. Value Types
      9. Self-Type Annotations
      10. Structural Types
      11. Existential Types
      12. Infinite Data Structures and Laziness
      13. Recap and What’s Next
    17. 13. Application Design
      1. Annotations
      2. Enumerations Versus Pattern Matching
      3. Thoughts On Annotations and Enumerations
      4. Using Nulls Versus Options
      5. Exceptions and the Alternatives
      6. Scalable Abstractions
      7. Effective Design of Traits
      8. Design Patterns
      9. Better Design with Design By Contract
      10. Recap and What’s Next
    18. 14. Scala Tools, Libraries, and IDE Support
      1. Command-Line Tools
      2. Build Tools
      3. Integration with IDEs
      4. Test-Driven Development in Scala
      5. Other Notable Scala Libraries and Tools
      6. Java Interoperability
      7. Java Library Interoperability
      8. Recap and What’s Next
    19. A. References
    20. Glossary
    21. Index
    22. About the Authors
    23. Colophon
    24. SPECIAL OFFER: Upgrade this ebook with O’Reilly

Java Interoperability

Of all the alternative JVM languages, Scala’s interoperability with Java source code is among the most seamless. This section begins with a discussion of interoperability with code written in Java. Once you understand the details, they can be generalized to address interoperability with other JVM languages, such as JRuby or Groovy. For example, if you already know how to use JRuby and Java together, and you know how to use Java and Scala together, then you can generalize to using JRuby and Scala together.

Because Scala syntax is primarily a superset of Java syntax, invoking Java code from Scala is usually straightforward. Going the other direction requires that you understand how some Scala features are encoded in ways that satisfy the JVM specification. We discuss several of the interoperability issues here. [Spiewak2009a] and [Odersky2008] provide additional information.

Java and Scala Generics

We have seen many examples of Scala code that uses Java types, such as java.lang.String and various java collection classes. Instantiating Java generic types is straightforward in Scala (since Scala version 2.7.0). Consider the following very simple Java generic class, JStack:

// code-examples/ToolsLibs/

import java.util.*;

public class JStack<T> {
  private List<T> stack = new ArrayList<T>();
  public void push(T t) {
  public T pop() {
    return stack.remove(stack.size() - 1);

We can instantiate it from Scala, specifying the type parameter, as shown ...

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