Java’s 8 Features

1. Lambda Expressions

Lambda expressions are a way to define anonymous functions (functions without a name) that can be passed as arguments to other methods. They are used primarily to implement simple instances of functional interfaces.

Syntax:

(parameters) -> expression

Example:

List<String> names = Arrays.asList("John", "Jane", "Jack", "Doe");
names.forEach(name -> System.out.println(name));

Explanation:
In the example above, name -> System.out.println(name) is a lambda expression that prints each name in the list.

2. Functional Interfaces

A functional interface is an interface with a single abstract method, and it can have multiple default or static methods. Lambda expressions are used to instantiate these interfaces.

Example:

@FunctionalInterface
interface Greeting {
    void sayHello();
}

Explanation:
Here, Greeting is a functional interface with a single abstract method sayHello.

3. Stream API

The Stream API is used to process sequences of elements (such as collections) in a functional-style. It provides methods to perform operations like filter, map, and reduce.

Example:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> evenNumbers = numbers.stream()
                                   .filter(n -> n % 2 == 0)
                                   .collect(Collectors.toList());
System.out.println(evenNumbers);

Explanation:
In the example, stream() creates a stream from the list of numbers, filter(n -> n % 2 == 0) filters out the even numbers, and collect(Collectors.toList()) collects the filtered results into a list.

4. Default Methods

Default methods are methods in an interface with a default implementation. They allow adding new methods to interfaces without breaking the implementing classes.

Example:

interface Vehicle {
    default void print() {
        System.out.println("I am a vehicle");
    }
}

class Car implements Vehicle {}

public class Main {
    public static void main(String[] args) {
        Car car = new Car();
        car.print();
    }
}

Explanation:
In the example, the Vehicle interface has a default method print. The Car class implements Vehicle and inherits the default method.

5. Optional Class

The Optional class is a container object which may or may not contain a non-null value. It is used to avoid NullPointerException and to handle null values gracefully.

Example:

Optional<String> optional = Optional.ofNullable("Hello");
optional.ifPresent(System.out::println);

Explanation:
In the example, Optional.ofNullable("Hello") creates an optional containing the string "Hello". The ifPresent method prints the value if it is present.

6. New Date and Time API

Java 8 introduced a new date and time API under the java.time package. It is more comprehensive and easier to use than the old java.util.Date and java.util.Calendar classes.

Example:

LocalDate today = LocalDate.now();
LocalDate birthday = LocalDate.of(1990, Month.FEBRUARY, 5);

Period age = Period.between(birthday, today);
System.out.println("Age: " + age.getYears());

Explanation:
In the example, LocalDate.now() gets the current date, and LocalDate.of(1990, Month.FEBRUARY, 5) creates a date for a specific birthday. Period.between(birthday, today) calculates the period between the two dates, which can be used to determine the age.

7. Nashorn JavaScript Engine

Nashorn is a JavaScript engine that allows you to run JavaScript code on the Java Virtual Machine (JVM).

Example:

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("nashorn");

try {
    engine.eval("print('Hello, Nashorn');");
} catch (ScriptException e) {
    e.printStackTrace();
}

Explanation:
In the example, ScriptEngineManager and ScriptEngine are used to evaluate and execute a JavaScript code snippet from within Java.

8. Method References

Method references provide a way to refer to methods without invoking them. They are a shorthand notation of a lambda expression to call a method.

Example:

List<String> names = Arrays.asList("John", "Jane", "Jack", "Doe");
names.forEach(System.out::println);

Explanation:
In the example, System.out::println is a method reference that refers to the println method of System.out.

9. Base64 Encoding and Decoding

Java 8 provides a Base64 class for encoding and decoding text using Base64 encoding scheme.

Example:

String originalInput = "test input";
String encodedString = Base64.getEncoder().encodeToString(originalInput.getBytes());
System.out.println(encodedString);

byte[] decodedBytes = Base64.getDecoder().decode(encodedString);
String decodedString = new String(decodedBytes);
System.out.println(decodedString);

Explanation:
In the example, Base64.getEncoder().encodeToString encodes a string into Base64 format, and Base64.getDecoder().decode decodes it back to the original string.