Closures and Higher-Order Functions

Closures and Higher-Order Functions

In this lesson — part of Advanced Features — you'll learn closures and higher-order functions in Java and why it matters in real work.

Why it matters

Functions that take or return functions unlock concise, composable code.

Key ideas

• Functions as values
• map / filter / reduce
• Callbacks
• Composition

In practice

Here's how it looks in idiomatic Java:

import java.util.List;
import java.util.stream.Collectors;

List<Integer> nums = List.of(1, 2, 3, 4, 5);
List<Integer> result = nums.stream()
        .filter(n -> n % 2 == 0)    // keep evens
        .map(n -> n * n)            // square them
        .collect(Collectors.toList());
System.out.println(result);         // [4, 16]

Java note: The Stream API is Java's idiomatic way to map/filter; streams are lazy and only execute when a terminal operation like collect runs.

Try it yourself

Exercise: In Java, use map and filter to get the squares of the even numbers.

Recap

You now understand closures and higher-order functions and can apply it in Java. Mark this lesson complete and continue to the next one.