Search⌘ K
AI Features
Home
Courses
Modern Java: From Fundamentals to Advanced Architecture

Encapsulation and Access Control

Explore how encapsulation safeguards object data in Java by using private access modifiers and public getter and setter methods. Understand how these controls prevent invalid state changes and promote reliable, maintainable code. This lesson helps you design well-encapsulated classes, balancing data hiding with controlled access to keep objects safe and consistent.

We'll cover the following...

Imagine a robot. We do not interact with its internal wires or battery cells directly. Instead, we use a control panel or specific buttons to give it commands. This outer casing protects the delicate internals from damage and ensures we don't accidentally short-circuit the system.

In Java, objects also need protection. Allowing any part of the code to modify an object's internal data directly can put it in an invalid state. For example, setting a robot's battery level to -50%. Encapsulation bundles data with protection mechanisms, ensuring objects stay safe, predictable, and valid.

The problem with uncontrolled access

Previously, we defined classes with public fields. While this is simple, it is also dangerous because it gives the outside world unrestricted access to modify an object's state.

Let's look at a Robot class that stores a battery level. Since the field is public, nothing stops us from assigning a nonsensical value.

For convenience, we are defining our class and our main method in the same file so you can see the code usage easily.

Java 25
class Robot {
    // Public field: accessible by anyone
    public int batteryLevel;
}
public class Main {
    public static void main(String[] args) {
        Robot bot = new Robot();
        
        // We can assign a negative battery level directly
        bot.batteryLevel = -50; 
        
        System.out.println("Battery Level: " + bot.batteryLevel + "%");
    }
}

  • Lines 1–3: We define a Robot class with a public integer field named batteryLevel.

  • Line 9: Because batteryLevel is public, the main method accesses it directly and assigns ...