Java Tutorial

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1. Lambdas and Functional Interfaces:

Java 8 introduced lambda expressions and functional interfaces, allowing you to write more concise and expressive code. Here's an example:


```java

// Functional interface with a single abstract method

@FunctionalInterface

interface Calculator {

    int calculate(int a, int b);

}


public class LambdaExample {

    public static void main(String[] args) {

        // Lambda expression using the Calculator functional interface

        Calculator addition = (a, b) -> a + b;

        System.out.println(addition.calculate(2, 3)); // Output: 5


        Calculator subtraction = (a, b) -> a - b;

        System.out.println(subtraction.calculate(5, 3)); // Output: 2

    }

}

```


2. Streams and Stream API:

Java 8 also introduced the Stream API, which provides a functional programming approach for processing collections of data. Here's an example:


```java

import java.util.Arrays;

import java.util.List;


public class StreamExample {

    public static void main(String[] args) {

        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);


        // Use stream to filter and map elements

        List<Integer> squaredEvenNumbers = numbers.stream()

                .filter(n -> n % 2 == 0)

                .map(n -> n * n)

                .collect(Collectors.toList());


        System.out.println(squaredEvenNumbers); // Output: [4, 16]

    }

}

```


3. Multithreading and Concurrency:

Java provides robust support for multithreading and concurrency. Here's an example using threads and synchronized blocks:


```java

public class Counter {

    private int count = 0;


    public synchronized void increment() {

        count++;

    }


    public static void main(String[] args) throws InterruptedException {

        Counter counter = new Counter();


        Runnable task = () -> {

            for (int i = 0; i < 1000; i++) {

                counter.increment();

            }

        };


        Thread thread1 = new Thread(task);

        Thread thread2 = new Thread(task);


        thread1.start();

        thread2.start();


        thread1.join();

        thread2.join();


        System.out.println(counter.count); // Output: 2000

    }

}

```


4. Generics:

Generics allow you to create reusable code that can work with different types. Here's an example using a generic class and method:


```java

public class Box<T> {

    private T content;


    public void add(T item) {

        content = item;

    }


    public T get() {

        return content;

    }


    public static void main(String[] args) {

        Box<String> stringBox = new Box<>();

        stringBox.add("Hello");

        String content = stringBox.get();

        System.out.println(content); // Output: Hello


        Box<Integer> integerBox = new Box<>();

        integerBox.add(42);

        int value = integerBox.get();

        System.out.println(value); // Output: 42

    }

}

```


5. Optional Class:

The Optional class helps avoid null pointer exceptions by providing a way to represent optional values. Here's an example:


```java

import java.util.Optional;


public class OptionalExample {

    public static void main(String[] args) {

        Optional<String> optionalValue = Optional.of("Hello");


        // Check if value is present

        if (optionalValue.isPresent()) {

            String value = optionalValue.get();

            System.out.println(value); // Output: Hello

        }


        // Use


 a default value if the optional value is empty

        String defaultValue = optionalValue.orElse("Default");

        System.out.println(defaultValue); // Output: Hello


        // Transform the optional value

        Optional<Integer> transformedValue = optionalValue.map(String::length);

        System.out.println(transformedValue.orElse(0)); // Output: 5

    }

}

```


These examples cover some advanced features of Java. 

Keep exploring the vast Java ecosystem and the official documentation to deepen your knowledge and leverage the full potential of the language.

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