Java 8 Tutorial:
Lambda Expressions, Streams, and More
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Following is a series of tutorials on the key new features of Java 8. Since each section includes exercises and exercise solutions, this can also be viewed as a self-paced Java 8 training course. These tutorials assume that you already know Java 5 or later; they focus on Java 8 topics that would not be understandable to those without at least
moderate knowledge of interfaces, inner classes, and collections.
If you don't already know the Java language, please see
the Java programming tutorial series. All the slides, source code, exercises, and exercise solutions are free for unrestricted use.
Although lambda expressions are not quite real functions, they are close enough for most purposes, and have very
succinct syntax that looks like Scala anonymous functions (minus the type declarations). Although it hardly makes
Java into Lisp, lambdas support a definite functional programming style that is long overdue in Java.
Streams are wrappers around collections that use lambdas pervasively. They support many operations that use lambdas, including "map", "reduce", "filter", and "forEach". They also support lazy evaluation, so if you map firstName over Employees, filter ones that start with "P", then choose the first, it really only maps and filters until the
first match. Streams can also be parallel, so that the operations are automatically done concurrently, without any explicit multithreading code.
Taken together, lambdas and streams result in by far the biggest change to Java programming since at least 2004, when generics and annotations were added to the language.
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