🚀 Java 8 Features (Must-Know)

Java 8 didn’t just add features, it quietly rewired how Java thinks 🧠⚙️ From verbose boilerplate to sleek, functional style… it’s like switching from a typewriter to a smart IDE.

Let’s break it down in a way you can use in interviews and code immediately.

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🔹 1. Lambda Expressions

👉 Write functions like mini one-liners instead of bulky anonymous classes

List<String> list = Arrays.asList("A", "B", "C");

// Before Java 8
for (String s : list) {
    System.out.println(s);
}

// Java 8
list.forEach(s -> System.out.println(s));

🎯 Use Case

• Functional programming
• Cleaner, concise code

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🔹 2. Functional Interfaces

👉 Interface with only one abstract method

Examples:

• Runnable
• Comparator

@FunctionalInterface
interface MyFunc {
    void apply();
}

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🔹 3. Stream API

👉 Process collections like a pipeline 🛠️

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

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

🎯 Key Operations

• filter() → select
• map() → transform
• collect() → gather

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🔹 4. Default Methods (Interface Enhancement)

👉 Interfaces can now have method implementations

interface MyInterface {
    default void sayHello() {
        System.out.println("Hello");
    }
}

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🔹 5. Method References

👉 Shortcut for lambda expressions

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

Instead of:

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

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🔹 6. Optional Class

👉 Avoid NullPointerException

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

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

🎯 Key Methods

• isPresent()
• orElse()
• orElseGet()

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🔹 7. Date & Time API (java.time)

👉 Modern replacement for old Date

LocalDate today = LocalDate.now();
LocalTime time = LocalTime.now();
LocalDateTime dt = LocalDateTime.now();

🎯 Benefits

• Immutable
• Thread-safe

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🔹 8. Collectors

👉 Used with streams

List<Integer> result = list.stream()
    .filter(n -> n > 2)
    .collect(Collectors.toList());

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🔹 9. Parallel Streams

👉 Easy multithreading

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

⚠️ Use carefully (not always faster)

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🔹 10. Nashorn JavaScript Engine

👉 Run JavaScript inside Java (rarely used now)

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🎯 Interview Answer (Perfect Summary)

“Java 8 introduced major features like lambda expressions, functional interfaces, Stream API, Optional class, default methods, method references, and a new Date-Time API. These features enable functional programming, improve readability, and reduce boilerplate code.”

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🧠 Real-World Impact

Before Java 8:

for loop everywhere 😓

After Java 8:

stream().filter().map().collect() 😎

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⚠️ Common Interview Traps

• Stream is not a data structure
• Optional should not be used for fields
• Parallel stream is not always faster

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🚀 Memory Trick

Think Java 8 = FLOOD

• Functional interfaces
• Lambda
• Optional
• Operations (Streams)
• Date-Time API

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