1Z0-809 - Java SE 8 Programmer II (OCP) Certification

Based on the topics covered in Test 3 for the Oracle Certified Professional Java SE 8 Programmer exam, let's explore each of the functional interface and Stream API concepts in more detail.

Lambda Built-in Functional Interfaces

Java SE 8 introduced the java.util.function package containing a number of predefined functional interfaces. These are:

1. Predicate: Takes one argument of type T and returns a boolean.

   • Example: Predicate<String> p = s -> s.length() > 5;

2. Consumer: Accepts one argument of type T and returns no result (a void return type).

   • Example: Consumer<String> c = System.out::println;

3. Function<T,R>: Takes an input of type T and produces a result of type R.

   • Example: Function<Integer, String> f = i -> "Result of " + i;

4. Supplier: Produces a result of type T with no input arguments.

   • Example: Supplier<String> s = () -> "Hello World";

5. UnaryOperator: A specialization of Function for objects of the same type (no need to import it).

   • Example: UnaryOperator<Integer> op = i -> i + 1;

6. BinaryOperator: A specialization of BiFunction for taking two arguments and producing a single result (also no need to import it).

   • Example: BinaryOperator<String> bo = (s1, s2) -> s1 + s2;

Java Stream API

The Stream API in Java SE 8 allows you to work with sequences of elements (such as collections) without explicitly iterating through them. The stream operations are declarative and functional by nature.

• Stream Creation: You can create a Stream from any collection, or from an array, or even generate a stream of data on the fly using methods like iterate() or generate().

  • Example: List<String> list = Arrays.asList("a", "b", "c"); List<String> distilledList = list.stream().filter(s -> s.length() > 2).collect(Collectors.toList());

• Intermediate Operations: These operations transform the stream, such as filter(), map(), sorted(), etc.

  • Example: list.stream().filter(s -> s.startsWith("a")).map(String::toUpperCase);

• Terminal Operations: These operations produce a result, such as forEach(), reduce(), collect(), etc.

  • Example: list.stream().filter(s -> s.length() > 2).collect(Collectors.toList());

• Parallel Streams: You can create parallel streams to perform computations in parallel by using the parallelStream() method instead of stream().

  • Example: list.parallelStream().filter(s -> s.length() > 2).collect(Collectors.toList());

NIO.2 (New I/O)

NIO.2 (New Input/Output) is a package in Java that provides modernized file system access and advanced, efficient network socket architecture for high-throughput and scalable Internet and multicast applications.

• Path Interface: A Path represents a pathname to a file or directory. You can manipulate paths without needing a FileSystem object.

  • Example: Path path = Paths.get("path/to/folder");

• Files Class: Provides a static factory methods for file operations and metadata, such as creating, copying, deleting, moving files, and retrieving file attributes.

  • Example: Files.deleteIfExists(path);

Localization

Java provides support for localization of text through its ResourceBundle class and the Locale class. You can use these to internationalize your Java applications.

• Locale: Represents a specific geographical, political, or cultural locale.

  • Example: Locale locale = new Locale("fr", "FR");

• Properties File: Stores localized text in a way that makes it easy to manage multiple language versions of the same data.

  • Example: ResourceBundle bundle = ResourceBundle.getBundle(bundleName, locale);

Concurrency

Java concurrency is designed to enable multiple threads to execute concurrently.

• Executors: Simplify the creation and management of threads. The ExecutorService interface provides a higher level abstraction for executing tasks asynchronously.

  • Example: ExecutorService executor = Executors.newFixedThreadPool(10);

• Concurrent Collections: Classes like CopyOnWriteArrayList are thread-safe variations of their non-concurrent counterparts.

  • Example: List<String> list = new CopyOnWriteArrayList<>();

• Fork/Join Framework: A concurrency framework for exploiting multi-core processors and improving the scalability, parallel performance, and maintainability of Java applications.

  • Example: ForkJoinTask<Void> task = new ForkJoinTask<>() { /* ... */ };

• Parallel Streams: You can execute stream pipelines in parallel by using parallel() on a stream.

  • Example: list.parallelStream().filter(s -> s.length() > 2).collect(Collectors.toList());

Building Database Applications with JDBC

JDBC (Java Database Connectivity) is an API for the execution of SQL statements in a database. It provides a uniform interface to various databases, and it's used to interact with databases within Java applications.

• DriverManager: Manages database drivers and connections to databases using a JDBC URL.

  • Example: Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/mydb", "user", "password");

• Statements and ResultSets: You use Statement objects to execute SQL statements, and ResultSet objects to iterate over the results returned by querying a database.

  • Example: Statement stmt = conn.createStatement();

Understanding these core Java concepts is essential for any developer working with Java, as they provide the foundation for building robust, scalable, and maintainable applications.