Data Hiding vs Encapsulation

The two terms are often used as if they meant the same thing, and interviewers like to ask for the difference. Data hiding is one technique: making fields inaccessible from outside, usually with private. Encapsulation is the bigger idea: bundling the data with the behavior and rules that keep it valid. You can hide data and still have no real protection, as the example below shows.

Hidden but Not Protected

public class Tickets {
    static class HiddenCounter {
        private int sold;
 
        public int getSold() { return sold; }
        public void setSold(int sold) { this.sold = sold; }
    }
 
    static class EncapsulatedCounter {
        private final int capacity;
        private int sold;
 
        EncapsulatedCounter(int capacity) { this.capacity = capacity; }
 
        public int getSold() { return sold; }
 
        public boolean sell(int count) {
            if (count <= 0 || sold + count > capacity) {
                return false;
            }
            sold += count;
            return true;
        }
    }
 
    public static void main(String[] args) {
        HiddenCounter hidden = new HiddenCounter();
        hidden.setSold(-5);
        System.out.println("Hidden counter sold: " + hidden.getSold());
 
        EncapsulatedCounter show = new EncapsulatedCounter(100);
        System.out.println("Sell 60: " + show.sell(60));
        System.out.println("Sell 50: " + show.sell(50));
        System.out.println("Sell -5: " + show.sell(-5));
        System.out.println("Show sold: " + show.getSold());
    }
}

Hidden counter sold: -5
Sell 60: true
Sell 50: false
Sell -5: false
Show sold: 60

How it works

1. HiddenCounter hides its field (private), but the setter accepts anything. "-5 tickets sold" is nonsense, yet nothing stops it. That's data hiding without encapsulation.
2. EncapsulatedCounter hides the field and owns the rules: the only way to change sold is sell, which refuses overselling and negative counts.
3. The show can never be overbooked, however the class is used.

Side by Side

Common Mistakes

Calling any class with private fields "encapsulated". If every field has an unchecked setter, the rules live outside the class.

Hiding data that callers really need. Encapsulation doesn't mean "no getters"; it means controlled access.

Interview Corner

Practice

1. Easy: Turn HiddenCounter into an encapsulated class by replacing setSold with methods that make sense for a ticket counter.
2. Harder: Add a cancel(int count) method to EncapsulatedCounter. Which rules does it need?

Key Takeaways