Java 8 FAQ: Top Questions

Java 8 provides several built-in functional interfaces in the java.util.function package. These interfaces represent common operations such as consuming, transforming, supplying, and testing values.

🗺️ Step-by-Step Overview:

1. Predicate<T>: Tests a value and returns a boolean.
2. Function<T, R>: Takes a value of type T and returns a value of type R.
3. Consumer<T>: Takes a value of type T and returns nothing.
4. Supplier<T>: Supplies a value of type T with no input.
5. UnaryOperator<T>: A Function where input and output types are the same.
6. BinaryOperator<T>: Takes two inputs of type T and returns a result of type T.

📥 Example Input:

Predicate isLong = str -> str.length() > 5;
Function intToStr = i -> "Value: " + i;
Consumer printer = s -> System.out.println(s);
Supplier random = () -> Math.random();

🏆 Expected Output:

true
Value: 10
[Printed String]
[Random Number]

✅ Java 8 Solution:

import java.util.function.*;

public class FunctionalInterfacesExample {
  public static void main(String[] args) {
    Predicate isLong = str -> str.length() > 5;
    System.out.println(isLong.test("Example"));

    Function intToStr = i -> "Value: " + i;
    System.out.println(intToStr.apply(10));

    Consumer printer = s -> System.out.println("Hello, " + s);
    printer.accept("World");

    Supplier random = () -> Math.random();
    System.out.println(random.get());
  }
}

📘 Detailed Explanation:

• Predicate: Used in filter() operations to test conditions.
• Function: Used in map() to transform values.
• Consumer: Used in forEach() to process each element.
• Supplier: Useful for lazy initialization or generating values on demand.
• Operator variants: Useful for arithmetic and transformation pipelines.

🛠️ Use Cases:

• Passing logic into methods like stream filters or processors.
• Creating expressive APIs with functional hooks.
• Replacing verbose anonymous inner classes in callbacks.