Java 8 is one of the most impactful updates to the Java programming language. It introduced several key features that fundamentally changed how developers write and structure their code.

Key Features of Java 8

• Lambda Expressions: This allows you to define anonymous functions, enhancing readability and reducing unnecessary code.

• Method References: A shorthand notation of a lambda expression to call a method. It simplifies code by allowing existing methods to be referenced directly.

            Example:

list.forEach(System.out::println);

• Functional Interfaces: Interfaces with a single abstract method. They can have multiple default or static methods.

            Example: Runnable, Callable, or custom interfaces.

• Stream API: Facilitates functional-style operations on collections, enabling efficient data processing with methods like filter, map, and reduce.

• Default Methods: Allow interfaces to have methods with a default implementation, enabling backward compatibility while adding new methods.

            Example:

interface MyInterface {
    default void defaultMethod() {
        System.out.println("Default");
    }

• Base64 Encode/Decode: Provides a way to encode and decode data in Base64 format using the java.util.Base64 class.

Example:

String encoded = Base64.getEncoder().encodeToString("Hello".getBytes());

• Static Methods in Interface: Interfaces can contain static methods that can be called independently of any instances.

Example:

interface MyInterface {
    static void staticMethod() {
        System.out.println("Static Method");
    }
}

• Optional Class: A container for optional values that helps avoid NullPointerExceptions by providing methods to handle the presence or absence of values.

Example:

Optional<String> optional = Optional.ofNullable(getValue());

• Collectors Class: Provides static methods to accumulate stream elements into collections or summarize statistics.

Example:

List<String> collected = stream.collect(Collectors.toList());

• ForEach() Method: A method in the Stream API that allows you to act as each element of the stream.

Example:

stream.forEach(System.out::println);

• Nashorn JavaScript Engine: A lightweight JavaScript engine that allows embedding JavaScript code in Java applications, replacing the older Rhino engine.

Example:

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

• Parallel Array Sorting: Introduces parallel sorting for arrays using the Arrays.parallelSort() method, which enhances performance on large datasets.

Example:

int[] array = {5, 3, 1, 2, 4};
Arrays.parallelSort(array);

• Type and Repeating Annotations: Java 8 allows for the definition of repeating annotations, enabling the same annotation to be applied multiple times to the same declaration.

Example:

@Repeatable(Schedules.class)
@interface Schedule {
    String day();
}

• IO Enhancements: New java.nio.file package for improved file handling, and the introduction of new methods in Files class for easier file I/O operations.

Example:

Path path = Paths.get("file.txt");
Files.lines(path).forEach(System.out::println);

• Concurrency Enhancements: Introduces new classes and methods for better handling of concurrent programming, including the CompletableFuture for asynchronous programming.

Example:

CompletableFuture.supplyAsync(() -> {
    // asynchronous task
    return result;
});

• JDBC Enhancements: Enhancements to JDBC include the introduction of the java.sql package, providing new methods for improved database operations.

Example: New Connection methods to manage SQL features like connection pooling.

Here, are the top Java 8 coding interview questions for freshers and experienced 2024:

1. Write a Java 8 program using a lambda expression to add two integers.

import java.util.function.BiFunction;

public class LambdaAddition {
    public static void main(String[] args) {
        BiFunction<Integer, Integer, Integer> add = (a, b) -> a + b;
        System.out.println(add.apply(5, 3)); // Output: 8
    }
}

2. Write a Java 8 program to filter and print even numbers from a list.

import java.util.Arrays;
import java.util.List;

public class FilterEvenNumbers {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
        numbers.stream()
               .filter(n -> n % 2 == 0)
               .forEach(System.out::println); // Output: 2 4 6
    }
}

3. Write a Java 8 program to map integers to their squares and print results.

import java.util.Arrays;
import java.util.List;

public class MapToSquares {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4);
        numbers.stream()
               .map(n -> n * n)
               .forEach(System.out::println); // Output: 1 4 9 16
    }
}

4. Write a Java 8 program to find and print the maximum value from a list.

import java.util.Arrays;
import java.util.List;

public class FindMaxValue {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
        int max = numbers.stream()
                         .max(Integer::compare)
                         .get();
                          System.out.println(max); // Output: 5
    }
}

5. Write a Java 8 program to count and print the number of elements in a list.

import java.util.Arrays;
import java.util.List;

public class CountElements {
    public static void main(String[] args) {
        List<String> words = Arrays.asList("apple", "banana", "pear");
        long count = words.stream().count();
        System.out.println(count); // Output: 3
    }
}

6. Write a Java 8 program to reduce a list of integers to their sum.

import java.util.Arrays;
import java.util.List;

public class ReduceToSum {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3);
        int sum = numbers.stream().reduce(0, Integer::sum);
        System.out.println(sum); // Output: 6
    }
}

7. Write a Java 8 program to print the lengths of strings in a list.

import java.util.Arrays;
import java.util.List;

public class PrintLengths {
    public static void main(String[] args) {
        List<String> words = Arrays.asList("Java", "Python", "JavaScript");
        words.forEach(word -> System.out.println(word.length())); // Output: 4 6 10
    }
}

8. Write a Java 8 program to print distinct elements from a list of integers.

import java.util.Arrays;
import java.util.List;

public class DistinctElements {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 2, 3, 4, 4);
        numbers.stream()
               .distinct()
               .forEach(System.out::println); // Output: 1 2 3 4
    }
}

9. Write a Java 8 program to print names sorted in alphabetical order from a list.

import java.util.Arrays;
import java.util.List;

public class SortedOrder {
    public static void main(String[] args) {
        List<String> names = Arrays.asList("Charlie", "Alice", "Bob");
        names.stream()
             .sorted()
             .forEach(System.out::println); // Output: Alice Bob Charlie
    }
}

10. Write a Java 8 program using Optional to check if a value is present.

import java.util.Optional;

public class OptionalExample {
    public static void main(String[] args) {
        Optional<String> name = Optional.of("Java");
        name.ifPresent(System.out::println); // Output: Java
    }
}

11. Write a Java 8 program to group strings by their lengths and print the groups.

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class GroupByLength {
    public static void main(String[] args) {
        List<String> words = Arrays.asList("a", "bb", "ccc", "dd");
        Map<Integer, List<String>> grouped = words.stream()
                                                  .collect(Collectors.groupingBy(String::length));
        System.out.println(grouped); // Output: {1=[a], 2=[bb, dd], 3=[ccc]}
    }
}

12. Write a Java 8 program to collect squares of numbers into a new list.

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class CollectToList {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3);
        List<Integer> squares = numbers.stream()
                                        .map(n -> n * n)
                                        .collect(Collectors.toList());
        System.out.println(squares); // Output: [1, 4, 9]
    }
}

13. Write a Java 8 program to limit and skip elements in a list, then print.

import java.util.Arrays;
import java.util.List;

public class LimitAndSkip {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
        numbers.stream()
               .limit(3)
               .forEach(System.out::println); // Output: 1 2 3
    }
}

14. Write a Java 8 program to find and print the first element in sorted order.

import java.util.Arrays;
import java.util.List;

public class FindFirst {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(5, 3, 1, 4, 2);
        int first = numbers.stream()
                           .sorted()
                           .findFirst()
                           .get();
        System.out.println(first); // Output: 1
    }
}

15. Write a Java 8 program to create a custom functional interface for addition.

@FunctionalInterface
interface MyFunction {
    int apply(int a, int b);
}

public class CustomFunctionalInterface {
    public static void main(String[] args) {
        MyFunction add = (a, b) -> a + b;
        System.out.println(add.apply(10, 20)); // Output: 30
    }
}

16. Write a Java 8 program using flatMap to print characters from lists of strings.

import java.util.Arrays;
import java.util.List;

public class FlatMapExample {
    public static void main(String[] args) {
        List<List<String>> list = Arrays.asList(
                Arrays.asList("A", "B"),
                Arrays.asList("C", "D"));
        list.stream()
            .flatMap(List::stream)
            .forEach(System.out::println); // Output: A B C D
    }
}

17. Write a Java 8 program using peek to print processed elements during a stream operation.

import java.util.Arrays;
import java.util.List;

public class PeekExample {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4);
        numbers.stream()
               .peek(n -> System.out.println("Processing: " + n))
               .map(n -> n * n)
               .forEach(System.out::println); // Output: Processing: 1, Processing: 2, ...
    }
}

18. Write a Java 8 program to create and print result from a CompletableFuture asynchronously.

import java.util.concurrent.CompletableFuture;

public class CompletableFutureExample {
    public static void main(String[] args) {
        CompletableFuture<Integer> future = CompletableFuture.supplyAsync(() -> 1 + 2);
        future.thenAccept(System.out::println); // Output: 3
    }
}

19. Write a Java 8 program using reduce to calculate the product of a list.

import java.util.Arrays;
import java.util.List;

public class CustomReduce {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3, 4);
        int prod = numbers.stream().reduce(1, (a, b) -> a * b);
        System.out.println(prod); // Output: 24
    }
}

20. Write a Java 8 program to check if any number in a list is even.

import java.util.Arrays;
import java.util.List;

public class AnyMatchExample {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.asList(1, 2, 3);
        boolean haseven = numbers.stream().anyMatch(n -> n % 2 == 0);
        System.out.println(haseven); // Output: true
    }
}

In conclusion, while preparing for Java 8 coding interviews, it’s crucial to focus on a variety of topics. Practice questions often involve writing code to manipulate collections using the Stream API. Solving Java 8 programming questions will sharpen your problem-solving skills and reinforce your understanding of modern Java features. Overall, consistent practice with Java 8 coding questions will help you excel in technical interviews.

1. What are some common Java 8 coding questions for experienced professionals?

Common questions include those related to Stream API, lambda expressions, and functional programming concepts. They may also involve practical coding challenges to test problem-solving skills.

2. How can I practice Java 8 coding problems?

You can practice by solving problems on coding platforms like LeetCode, and HackerRank, or by working on personal projects that include Java 8 features.

3. What is the importance of the Stream API in Java 8?

The Stream API significantly simplifies data manipulation and enhances performance through parallel processing and functional programming techniques.

4. Are there any resources for Java 8 programming interview questions?

Yes, many online platforms, books, and coding challenge websites offer extensive resources on Java 8 interview questions and coding exercises.