Jump-Starting Lambda Programming

Stuart Marks introduces the concept of lambda expressions in Java, explaining them as anonymous functions that allow treating code as data. He contrasts this introductory presentation to more complex ones by Brian Goetz, focusing on the basics of lambda, its integration in Java 8, and its impact on programming style. Lambda expressions enable parameterizing behavior, which is a significant shift from Java 7's capabilities. The talk promises a practical exploration of lambda through an example program, demonstrating its application in everyday tasks and complex programming scenarios like parallel programming.

The paragraph delves into practical use cases of lambda expressions for filtering and selecting data based on certain criteria. It uses the example of a 'Person' object and a list of persons to illustrate how lambda can be used to select individuals based on attributes like age and sex. The discussion includes scenarios like selecting eligible drivers, voters, and individuals of legal drinking age, highlighting the flexibility of lambda for various programming tasks. It also touches on the problem of duplicated code and the solution of parameterizing values to streamline the process.

This section discusses the enhancement of programming flexibility through parameterized methods using lambda expressions. It explains how to refactor methods to accept parameters that define the behavior of the method, such as age limits for different use cases. The paragraph also addresses the complexity introduced by meta-information and the challenges of value parameterization when every value is potentially legal. The solution presented is to use lambda expressions to parameterize behavior instead of values, leading to cleaner and more maintainable code.

The speaker introduces the concept of functions in Java, distinguishing them from Java's traditional approach to method invocation. Functions are defined as pieces of computation that take parameters and return values. The paragraph explains the notation used to describe functions and provides examples of different kinds of functions. It also discusses 'functional interfaces' — interfaces with a single method, which are key to utilizing lambda expressions in Java. The concept of a 'predicate' is highlighted as a common case for functions that take an object and return a boolean.

The paragraph demonstrates the practical application of lambda expressions in Java by refactoring the robocalling example. It shows how to use lambda expressions to replace anonymous inner classes, making the code more concise and easier to understand. The use of lambda expressions allows the caller to parameterize behavior directly within the method call, which is more efficient than creating separate methods or classes for each behavior. The paragraph also emphasizes the importance of functional interfaces in enabling this feature of Java 8.

This section explores how lambda expressions can be used to streamline code by eliminating boilerplate code associated with anonymous inner classes. It discusses the concept of 'expression lambdas' and 'statement lambdas,' showing how they can be used to create more expressive and flexible code. The paragraph also explains how lambda expressions are converted into instances of functional interfaces by the Java compiler, which performs type inference to determine the types of parameters.

The speaker continues to refactor the example code, introducing functional interfaces like 'Block' and 'Mapper' to further parameterize behavior. The paragraph explains how these interfaces can be used to create more generic and reusable code. It also discusses the concept of a 'pipeline' of operations, where a stream of objects is filtered, mapped, and then processed by a block of code. The paragraph emphasizes the flexibility and power of this approach, allowing for easy rearrangement and extension of code.

The paragraph introduces the Stream API in Java, which represents a stream of values and allows for the creation of a pipeline of operations that can be executed in parallel. It explains how to convert a list into a stream and how to apply filter, map, and for-each operations within a pipeline. The paragraph also discusses the ease of introducing parallelism into the pipeline by simply changing a stream call to a parallel stream, highlighting the simplicity of writing parallel programs with lambda expressions.

This section discusses the considerations that need to be taken into account when writing parallel programs using lambda expressions and the Stream API. It introduces the 'Prime Directive Against Non Interference,' which states that lambda expressions must not have side effects or dependencies on the order of execution. The paragraph also mentions the importance of using thread-safe data structures when writing parallel code and provides a recap of the new features introduced in Java 8 for functional programming and parallelism.

The final paragraph wraps up the presentation by summarizing the key points about lambda expressions and the new APIs introduced in Java 8. It emphasizes the power and flexibility that lambda brings to Java, allowing for expressive and powerful programming, as well as the ease of writing parallel programs. The speaker also provides references for further information, including talks by Brian Goetz and resources related to the lambda project. The paragraph concludes by inviting questions from the audience.