Encapsulation

What a session covers

The tutor works through these with you, in conversation and code. A session ends when you have shown them, not when a video does.

1. Explain what an invariant is and how private fields protect it
2. Write a class that exposes behaviour instead of setters
3. Spot the generated setter that lets a caller break the invariant

In practice

A few lines that show Encapsulation doing its job.

public class Account {
    private long balanceCents;

    public void withdraw(long cents) {
        if (cents <= 0) throw new IllegalArgumentException("amount must be positive");
        if (cents > balanceCents) throw new InsufficientFundsException(balanceCents, cents);
        balanceCents -= cents;
    }

    public long balanceCents() { return balanceCents; }
}

The common mistake

What to know first

Your roadmap puts these before Encapsulation, unless you already know them.

• Records and var

How it stays learned

Once a session shows you understand Encapsulation, it comes back for review. Each review takes a minute and tells the memory model how well you still know it.

1. Day 3First recall, while it is fresh
2. Day 7Second, a week on
3. Day 18Last, when it has settled

Where it leads

Topics that build on Encapsulation.

• Threads and thread safety