Lesson 24: Nested & Inner Classes

Inner classes tie tightly to their enclosing instance — useful when a helper type only makes sense in the context of its outer class.

Real-time example

A LinkedList implementation defines a private Node inner class — nobody outside the list should ever construct a Node directly.

class TaskQueue {
    private class Task {
        String name;
        Task(String name) { this.name = name; }
    }
    private List<Task> tasks = new ArrayList<>();
    void add(String name) { tasks.add(new Task(name)); }
    int size() { return tasks.size(); }
}

What's happening

Task is private to TaskQueue — it literally cannot leak outside, which is the encapsulation win of inner classes.

Use a static nested class instead if the inner type doesn't need access to the outer instance's fields.