Access Modifiers in Java

What are access modifiers

Access modifiers control who can use a class, field or method. They let you hide internal details and expose only what should be public. Java has four levels, from fully open (public) to fully closed (private). They are the foundation of encapsulation.

The four modifiers

• public — accessible from anywhere.
• private — accessible only within the same class.
• protected — accessible in the same package and by subclasses.
• default (no keyword) — accessible only within the same package.

You choose the most restrictive level that still lets your code work — this keeps data safe.

private and encapsulation

class Account {
    private double balance = 0;   // hidden data
}
// Account a = new Account();
// a.balance = -500;   // ERROR: balance is private

Making balance private stops outside code from changing it directly — for example setting a negative balance. This is encapsulation: the field is hidden and protected.

Getters and setters

class Account {
    private double balance = 0;

    public double getBalance() {      // getter
        return balance;
    }
    public void deposit(double amt) { // controlled setter
        if (amt > 0) balance += amt;  // validation!
    }
}

Public methods give controlled access to a private field. The deposit method validates the amount before changing balance — something you cannot enforce with a public field.

protected and default

• protected — used when subclasses (even in other packages) need access, but the public should not.
• default — written by using no modifier; the member is visible only inside its own package.

These middle levels are less common than public and private, but useful for package and inheritance design.

Quick comparison

Common mistakes

• Making all fields public. Keep fields private and expose them via methods.
• Confusing default with public. No modifier means package-private, not public.
• Overusing protected. Use it only when subclasses genuinely need access.
• Skipping validation in setters. The point of a setter is to check values before setting.

Summary

• Access modifiers control who can use a class member.
• public is open everywhere; private is same-class only.
• protected adds subclasses; default is package-only.
• Keep fields private and expose them through getters/setters — encapsulation.
• Setters can validate values before changing private data.

Next, revise data hiding with classes and objects, or learn the static keyword.