What are the key features introduced in Java 8? Provide examples of lambda expressions and functional programming in Java.
Java 8 introduced several key features that significantly enhanced the language and opened up new possibilities for developers. Here's an in-depth answer explaining some of the key features introduced in Java 8, including lambda expressions and functional programming:
1. Lambda Expressions:
Lambda expressions are a powerful feature introduced in Java 8 that enables functional programming in Java. They provide a concise way to represent anonymous functions, allowing developers to write more compact and expressive code. Lambda expressions are primarily used in functional interfaces, which are interfaces with a single abstract method. Some key points about lambda expressions include:
* Syntax: Lambda expressions consist of a set of parameters, an arrow operator (`->`), and a body. The parameters represent the input to the function, the arrow operator separates the parameters from the body, and the body contains the code to be executed.
* Compactness: Lambda expressions eliminate the need to write verbose anonymous inner classes, reducing the code size and improving readability.
* Functional Interfaces: Lambda expressions are most commonly used in conjunction with functional interfaces, which provide the target type for the lambda expression.
* Example: Here's an example of a lambda expression that squares an integer:
```
java`Function<Integer, Integer> square = x -> x * x;`
```
In this example, the lambda expression `x -> x * x` represents an anonymous function that takes an integer `x` as input and returns its square.
2. Functional Interfaces:
Java 8 introduced the `java.util.function` package, which includes a set of predefined functional interfaces that facilitate functional programming in Java. Functional interfaces represent single abstract methods and are designed to be used with lambda expressions. Some commonly used functional interfaces include:
* `Predicate<T>`: Represents a function that takes an argument of type `T` and returns a boolean value.
* `Function<T, R>`: Represents a function that takes an argument of type `T` and returns a result of type `R`.
* `Consumer<T>`: Represents a function that takes an argument of type `T` and performs an action without returning a result.
* `Supplier<T>`: Represents a function that does not take any arguments but produces a result of type `T`.
3. Stream API:
Java 8 introduced the Stream API, which provides a fluent and functional way to process collections of data. Streams allow for concise and efficient manipulation of data using operations such as filtering, mapping, reducing, and more. Some key features of the Stream API include:
* Pipelining: Streams allow you to chain multiple operations together to form a pipeline. Each operation is applied to the stream elements, one by one, in a sequential or parallel manner.
* Lazy Evaluation: Streams employ lazy evaluation, meaning that the operations are executed only when needed. This allows for optimized performance by avoiding unnecessary computations.
* Example: Here's an example that demonstrates the use of the Stream API to filter and transform a list of integers:
```
java`List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
List<Integer> evenSquares = numbers.stream()
.filter(n -> n % 2 == 0)
.map(n -> n * n)
.collect(Collectors.toList());`
```
In this example, the stream is created from the list of numbers. The `filter` operation selects only the even numbers, and the `map` operation squares each number. Finally, the `collect` operation collects the results into a new list.
These are just a few of the key features introduced in Java 8. The addition of lambda expressions, functional interfaces, and the Stream API has made Java more expressive, concise, and capable of embracing functional programming paradigms. These