Functions, Anonymous Inner Classes, and Lambdas/Procs in Font

Printing Data Matrix 2d barcode in Font Functions, Anonymous Inner Classes, and Lambdas/Procs

The Java construct to pass units of computation as parameters to methods is anonymous inner classes. The use of anonymous inner classes was popularized with the Swing UI libraries. In Swing, most UI events are handled by interfaces that have one or two methods on them. The programmer passes the handlers by instantiating an anonymous inner class that has access to the private data of the enclosing class. Scala s functions are anonymous inner classes. Scala functions implement a uniform API with the apply method being the thing that s invoked. The syntax for creating functions in Scala is much more economical than the three or four lines of boilerplate for creating anonymous inner classes in Java. Additionally, the rules for accessing variables in the local scope are more flexible in Scala. In Java, an anonymous inner class can only access final variables. In Scala, a function can access and mutate vars.

Ruby has a collection of overlapping features that allow passing blocks, Procs, and lambdas as parameters to methods. These constructs have subtle differences in Ruby, but at their core, they are chunks of code that reference variables in the scope that they were created. Ruby also parses blocks such that block of code that are passed as parameters in method calls are syntactically identical to code blocks in while and if statements. Scala has much in common with Ruby in terms of an object model and function passing. Scala has much in common with Java in terms of uniform access to the same code libraries and static typing. It s my opinion that Scala has taken the best of both Java and Ruby and blended these things together in a very cohesive whole.

Summary

We ve covered a lot of ground in this chapter. We looked at how to build and run Scala programs. We walked through a bunch of Scala programs that demonstrated various aspects of Scala. We did an overview of Scala s syntax and basic constructs. In the next chapter, we re going to explore a bunch of Scala s data types that allow you to write powerful programs in very few lines of code with very few bugs.

n this chapter, we re going to explore Scala s collections classes and how to use them. Most Scala collection classes are immutable, meaning that once they are instantiated, the instances cannot be changed. You re used to immutability, as Java Strings are immutable. The conjunction of collections being immutable and providing powerful iteration features leads to more concise, higher-performance code that does extremely well in multicore, multithreaded concurrency situations.

In Java, the most commonly used types are immutable. Once an instance is created, it cannot be changed. In Java, String, int, long, double, and boolean are all immutable data types. Of these, String is a subclass of Object. Once a String is created, it cannot be changed. This has lots of benefits. You don t have to synchronize access to a String, even if it is shared by many threads, because there s no chance that it will be modified while another thread is accessing it. You don t have to keep a private copy of a String in case another method modifies it out from under you. When you pass String and other immutable types around in a Java program, you don t have to be defensive about using the instance. You can store it without fear that another method or thread will toLowerCase it. Using immutable data structures means less defensive programming, fewer defects, and, in most cases, better performance. So, you ask, why doesn t Java have a lot more immutable data structures There are two ends of the programming spectrum: the how end and the what end. Assembly language is at the far end of the how part of the spectrum. When you program in assembly language, you direct the CPU to move bytes around memory, perform arithmetic operations and tests, and change the program counter. These directions imperatives if you will direct the computer s operation (in other words, we tell it how to do its tasks). C is a thin layer on top of assembly language and continues to be a language oriented toward directing the steps that the CPU will take.