Intermediate 25 min read

Encapsulation

By the end of this lesson, you'll be able to:

Define encapsulation as bundling data with the logic that protects it
Explain why encapsulation reduces bugs caused by invalid state
Refactor a class with exposed fields into one with proper encapsulation

Prerequisites: Module 10: "Classes and Objects"

Naming what Module 10 already previewed

The private balance + public getBalance() pattern from Module 10's Access Modifiers lesson has a name: encapsulation. It's the first of the four core object-oriented principles this module covers — encapsulation, inheritance, polymorphism, and (via composition) code reuse without inheritance.

A real business example: Fleet Management

public class DeliveryVehicle {
    private Decimal fuelLevel;

    public DeliveryVehicle(Decimal startingFuel) {
        this.fuelLevel = startingFuel;
    }

    public void refuel(Decimal amount) {
        if (amount > 0) {
            fuelLevel += amount;
        }
    }

    public Decimal getFuelLevel() {
        return fuelLevel;
    }
}

fuelLevel can never go directly negative or be corrupted from outside — every change is forced through refuel(), which can enforce rules like "only positive amounts count." A fleet system with hundreds of vehicles stays trustworthy because no code anywhere can bypass this.

What breaks without encapsulation

public class DeliveryVehicle {
    public Decimal fuelLevel; // no protection at all
}

DeliveryVehicle van = new DeliveryVehicle();
van.fuelLevel = -9999; // perfectly legal, completely nonsensical

With a public field, literally any code anywhere in the org can set fuelLevel to anything, including impossible values — and there's no single place to add a rule later, because every caller touches the field directly instead of going through shared logic.

Exercise

Refactor this class so odometerReading is private, only increases through a method addDistance(Decimal km) that ignores negative input.

Show hint

private Decimal odometerReading; public void addDistance(Decimal km) { if (km > 0) { odometerReading += km; } }

APEX

Encapsulation Quiz

1. What does encapsulation protect against?

Outside code putting an object's data into an invalid state Slow-running methods Governor limit errors Compilation errors only

My Notes

Questions about this lesson

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Summary

Encapsulation means bundling an object's data together with the methods that are allowed to change it, so nothing outside the class can put that data into an invalid state.

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