LESSON 628 OF 671 · OBJECT-ORIENTED PROGRAMMING

Access Modifiers in Java

Lesson

TL ; DR:

An access modifier controls who can see a member of a class. The two you'll use most are public (anyone) and private (only this class).

Make data private so callers can't break invariants. Expose what they need through public methods (often called getters and setters):

class Dog {
    private String name;

    public Dog(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

Outside the class, rex.name is a compile error. Use rex.getName() instead.

Full lesson:

So far every field we wrote was public. That's convenient, but leaks internals. If you later decide to validate or compute the value differently, every caller in the codebase breaks.

Encapsulation

Encapsulation is the idea that an object's data should be hidden behind methods. The class controls how it's read and written; outside code only sees the API.

class Account {
    private double balance;

    public void deposit(double amount) {
        if (amount < 0) throw new IllegalArgumentException();
        balance += amount;
    }
}

The four Java modifiers

`public`	Visible everywhere.
`private`	Visible only inside the same class.
`protected`	Same package + subclasses.
(no modifier)	Package-private — only the same package.

For now, focus on public and private.

Your task

The Dog class's name field is now private. Add a public String getName() method that returns it.

Dog's name: Rex

STEP 1 OF 2

Guided

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