Java 8 Features

March 4, 2026

Short Overview:
Java 8 introduced functional programming features, Stream API, Lambda expressions, and many enhancements that changed how Java is written.

Major Java 8 Features

Lambda Expressions
Functional Interfaces
Stream API
Default & Static Methods in Interface
Method References
Optional Class
Date and Time API
forEach() Method
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1️⃣ Lambda Expressions

Short: Enables functional programming.

List list = Arrays.asList("Java","Spring");

list.forEach(s -> System.out.println(s));

Reduces boilerplate code.

2️⃣ Functional Interface

Short: Interface with exactly one abstract method.

@FunctionalInterface
interface MyInterface {
    void show();
}

Built-in examples: Runnable, Comparator, Predicate.

3️⃣ Stream API

Short: Process collections functionally.

List list = Arrays.asList(1,2,3,4);

list.stream()
    .filter(n -> n % 2 == 0)
    .forEach(System.out::println);

Operations:

filter()
map()
sorted()
collect()

4️⃣ Default & Static Methods in Interface

Short: Allows method implementation inside interface.

interface Test {
    default void show() {
        System.out.println("Default Method");
    }

    static void display() {
        System.out.println("Static Method");
    }
}

5️⃣ Method References

Short: Shortcut for lambda.

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

Types:

Class::staticMethod
Object::instanceMethod
Class::new

6️⃣ Optional Class

Short: Avoid NullPointerException.

Optional name = Optional.ofNullable(null);

System.out.println(name.orElse("Default"));

7️⃣ New Date and Time API

Short: Modern date/time handling.

LocalDate date = LocalDate.now();
LocalDateTime time = LocalDateTime.now();

Classes:

LocalDate
LocalTime
LocalDateTime
ZonedDateTime

8️⃣ forEach() Method

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

Frequently Asked Interview Questions (With Answers)

1️⃣ What is Lambda Expression?

Anonymous function that provides implementation of functional interface.

2️⃣ What is Functional Interface?

Interface with one abstract method.

3️⃣ Difference between map() and flatMap()?

map() transforms elements; flatMap() flattens nested structures.

4️⃣ What is Optional used for?

To avoid NullPointerException.

5️⃣ Difference between default and static methods in interface?

Default method can be overridden; static cannot.

6️⃣ What is Stream?

Sequence of elements supporting functional operations.

7️⃣ What is method reference?

Short form of lambda using :: operator.

Advanced Interview Points

Streams are lazy in nature.
Intermediate vs Terminal operations.
Parallel streams improve performance.
Optional is container object.
Functional programming introduced in Java 8.

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