Java SE 8 Lambdas and Streams - Java: How to Program Early Objects - page 769

•For String s, the natural order is case sensitive, which means that "Z" is less than "a" . Passing the
predefined Comparator String.CASE_INSENSITIVE_ORDER performs a case-insensitive sort.
Section 17.5.3 Filtering String s Then Sorting Them in Case-Insensitive Descending
Order
• Functional interface Comparator 's default method reversed (p. 748) reverses an existing Com-
parator 's ordering.
Section 17.6.1 Creating and Displaying a List<Employee>
• When the instance method reference System.out::println is passed to Stream method forEach ,
it's converted by the compiler into an object that implements the Consumer functional interface.
This interface's accept method receives one argument and returns void . In this case, the accept
method passes the argument to the System.out object's println instance method.
Section 17.6.2 Filtering Employee s with Salaries in a Specified Range
• To reuse a lambda, you can assign it to a variable of the appropriate functional interface type.
•The Comparator interface's static method comparing (p. 753) receives a Function that's used to
extract a value from an object in the stream for use in comparisons and returns a Comparator object.
• A nice performance feature of lazy evaluation is the ability to perform short circuit evaluation—
that is, to stop processing the stream pipeline as soon as the desired result is available.
• Stream method findFirst is a short-circuiting terminal operation that processes the stream pipe-
line and terminates processing as soon as the first object from the stream pipeline is found. The
method returns an Optional containing the object that was found, if any.
Section 17.6.3 Sorting Employee s By Multiple Fields
• To sort objects by two fields, you create a Comparator that uses two Function s. First you call Com-
parator method comparing to create a Comparator with the first Function . On the resulting Com-
parator , you call method thenComparing with the second Function . The resulting Comparator
compares objects using the first Function then, for objects that are equal, compares them by the
second Function .
Section 17.6.4 Mapping Employee s to Unique Last Name String s
• You can map objects in a stream to different types to produce another stream with the same num-
ber of elements as the original stream.
• Stream method distinct (p. 754) eliminates duplicate objects in a stream.
Section 17.6.5 Grouping Employee s By Department
• Collectors static method groupingBy (p. 755) with one argument receives a Function that clas-
sifies objects in the stream—the values returned by this function are used as the keys in a Map . The
corresponding values, by default, are List s containing the stream elements in a given category.
• Map method forEach performs an operation on each key-value pair. The method receives an ob-
ject that implements functional interface BiConsumer . This interface's accept method has two
parameters. For Map s, the first represents the key and the second the corresponding value.
Section 17.6.6 Counting the Number of Employee s in Each Department
• Collectors static method groupingBy with two arguments receives a Function that classifies
the objects in the stream and another Collector (known as the downstream Collector ; p. 756).
• Collectors static method counting returns a Collector that counts the number of objects in
a given classification, rather than collecting them into a List .