Java 8 FAQ: Top Questions

The map() method is an intermediate operation in the Java 8 Stream API that applies a transformation function to each element of the stream. It is used to convert elements from one form to another.

🗺️ Step-by-Step Instructions:

1. Use map() to apply a function to every element in the stream.
2. Each input element is transformed individually and returns a new stream.
3. Common transformations include converting data types, applying business rules, or formatting output.

📥 Example Input:

List names = Arrays.asList("alice", "bob", "claire");

List uppercased = names.stream()
                               .map(String::toUpperCase)
                               .collect(Collectors.toList());

🏆 Expected Output:

[ALICE, BOB, CLAIRE]

✅ Java 8 Solution:

import java.util.*;
import java.util.stream.*;

public class StreamMapExample {
  public static void main(String[] args) {
    List names = Arrays.asList("alice", "bob", "claire");

    List uppercased = names.stream()
                                   .map(String::toUpperCase)
                                   .collect(Collectors.toList());

    System.out.println(uppercased);
  }
}

📘 Detailed Explanation:

• map(): Applies a transformation function to each element.
• Returns: A new stream with the transformed elements.
• Common usage: Formatting strings, converting types, applying computations.

🛠️ Use Cases:

• Converting numeric values (e.g., from int to double).
• Formatting names or data before display.
• Applying business logic transformations in a clean way.