Most Commonly Java Interview Question in Java 8: What is Optional in Java 8?

 

Optional in Java 8:

In Java 8, Optional is a container object introduced in the java.util package. It is used to represent a value that can either be present (non-null) or absent (null). It provides a way to avoid NullPointerException (NPE) and improve code readability when dealing with nullable values.

Key Characteristics of Optional:

1. Avoids Null Checks: Provides methods to handle nullable values without explicit null checks.
2. Immutable: The Optional object is immutable, meaning its value cannot be changed once set.
3. Improves Readability: It reduces boilerplate code and enhances readability when handling optional or nullable values.

Common Methods in Optional:

1. Creating an Optional:
• Optional.of(T value): Creates an Optional with a non-null value. Throws NullPointerException if the value is null.
• Optional.ofNullable(T value): Creates an Optional that can hold a null or non-null value.
• Optional.empty(): Returns an empty Optional.
2. Checking for Value:
• isPresent(): Returns true if a value is present, otherwise false.
• isEmpty(): Returns true if no value is present, otherwise false.
3. Retrieving the Value:
• get(): Returns the value if present; otherwise, throws NoSuchElementException.
• orElse(T other): Returns the value if present; otherwise, returns the provided default value.
• orElseGet(Supplier<? extends T> supplier): Returns the value if present; otherwise, invokes the supplier and returns its result.
• orElseThrow(Supplier<? extends X> exceptionSupplier): Returns the value if present; otherwise, throws an exception provided by the supplier.
4. Processing the Value:
• ifPresent(Consumer<? super T> action): Executes the given action if a value is present.
• map(Function<? super T, ? extends U> mapper): Applies a mapping function if a value is present and returns a new Optional.
• flatMap(Function<? super T, Optional<U>> mapper): Similar to map but avoids nested Optional.

Example Usage:

1.       Basic Usage

Optional<String> optional = Optional.ofNullable("Hello, World!");

 

if (optional.isPresent()) {

    System.out.println(optional.get()); // Output: Hello, World!

} else {

    System.out.println("No value present.");

}

2. Using orElse and ifPresent

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

 

// Using orElse

String result = optional.orElse("Default Value");

System.out.println(result); // Output: Default Value

 

// Using ifPresent

optional.ifPresent(value -> System.out.println("Value: " + value)); // Does nothing

 

3.      Using map and flatMap

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

 

Optional<Integer> lengthOptional = optional.map(String::length);

lengthOptional.ifPresent(System.out::println); // Output: 5

 

Benefits of Optional:

1. Eliminates the risk of NullPointerException.
2. Promotes functional programming by using methods like map, flatMap, and ifPresent.
3. Makes the code more expressive and easier to understand.

 

Java Interview Question : JAVA Collection vs. Collections

 

java.util.Collection 

What it is: Collection is an interface that represents the root of the collection hierarchy in the Java Collections Framework. It defines the common behavior for a group of objects, known as its elements.

Purpose: It acts as a blueprint for all concrete collection types (like Lists, Sets, and Queues) that store individual elements. It specifies the basic operations that all collections should support.

import java.util.*;

public class CollectionExample {

    public static void main(String[] args) {

        Collection<String> names = new ArrayList<>(); // ArrayList implements List, which extends Collection

        names.add("Akshay");

        names.add("Ajay");

        names.add("Abhay");

        System.out.println("Collection elements: " + names); // Output: [Akshay, Ajay, Abhay]

       

        names.remove("Akshay");

        System.out.println("After removing Akshay: " + names); // Output: [Ajay, Abhay]

        System.out.println("Size: " + names.size()); // Output: 2

    }

}

java.util.Collections 

What it is: Collections is a utility class that provides static methods that operate on or return collections. It's like a helper class for the Collection interfaces and their implementations.

Purpose: It offers various polymorphic algorithms and utility methods that can be applied to Collection objects (or their sub-interfaces like List and Set). These methods include sorting, searching, shuffling, reversing, and creating thread-safe or unmodifiable versions of collections.

import java.util.*;

public class CollectionsExample {

    public static void main(String[] args) {

        List<Integer> numbers = new ArrayList<>();

        numbers.add(5);

        numbers.add(2);

        numbers.add(8);

        numbers.add(1);

        System.out.println("Original List: " + numbers); // Output: [5, 2, 8, 1]

        // Using Collections.sort()

        Collections.sort(numbers);

        System.out.println("Sorted List: " + numbers); // Output: [1, 2, 5, 8]

        // Using Collections.reverse()

        Collections.reverse(numbers);

        System.out.println("Reversed List: " + numbers); // Output: [8, 5, 2, 1]

        // Using Collections.max()

        System.out.println("Maximum element: " + Collections.max(numbers)); // Output: 8

        // Creating an unmodifiable list

        List<String> immutableList = Collections.unmodifiableList(List.of("apple", "banana"));

        // immutableList.add("orange"); // This would throw UnsupportedOperationException

        System.out.println("Immutable List: " + immutableList); // Output: [apple, banana]

    }

}

Java 8 Stream API MCQ for Interview

 Question: Which of the following operations is a terminal operation in Java 8 Stream API?

Options:

A. map()

B. filter()

C. collect()

D. flatMap()

Answer:

C. collect()

Explanation:

The collect() method is a terminal operation in the Stream API, used to transform the elements of a stream into a collection, list, or another data structure. Terminal operations produce a result or a side-effect and close the stream.

Master the Java 8 Stream API concepts to stand out in your interviews!

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