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New and Enhanced APIs That Take Advantage of Lambda Expressions and Streams in Java SE 8

In Java SE 8, new classes have been added and existing classes have been enhanced to take advantage of lambda expressions and streams, which are described in the lesson Aggregate Operations in the Java Tutorials. You can find most of these new and enhanced classes in the following packages:

• java.util: An existing package which, in addition to the java.lang.invoke package, integrates the Java Collections Framework with streams and provides general utility functionality used by streams.
• java.util.function: A new package that contains general purpose functional interfaces that provide target types for lambda expressions and method references.
• java.util.stream: A new package that contains the majority of interfaces and classes that provide functionality to streams and aggregate operations

Many additions to existing classes take advantage of streams. Other additions include methods that accept instances of functional interfaces, which you can invoke with lambda expressions or method references.

New Packages

Modified Packages

Classes such as Boolean, Integer, and other object wrapper classes for primitive types (see Autoboxing and Unboxing) are listed here because they have been enhanced with methods that are suitable for targets of method references. For example, you can use the method Integer.sum as a method reference, as demonstrated in the following example that adds integers contained in a list:

Integer[] intArray = {1, 2, 3, 4, 5, 6, 7, 8 };
List<Integer> listOfIntegers =
    new ArrayList<>(Arrays.asList(intArray));
    System.out.println("Sum of integers: " +
        listOfIntegers
            .stream()
            .reduce(Integer::sum).get());

(Note that you can also add integers contained in a stream with the method IntStream.sum.)

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