Information Hiding

Part of the Object Oriented Programming section of Coddy's Java journey — lesson 12 of 87.

Information hiding is the principle of restricting direct access to an object's internal data. By combining private fields with getters and setters, you create a protective barrier around your object's state.

Consider what happens without information hiding:

public class Temperature {
    public double celsius;  // Exposed directly
}

// Anyone can set invalid values
Temperature t = new Temperature();
t.celsius = -500;  // Below absolute zero - impossible!

With information hiding, you control how data is accessed and modified:

public class Temperature {
    private double celsius;
    
    public void setCelsius(double celsius) {
        if (celsius >= -273.15) {
            this.celsius = celsius;
        }
    }
    
    public double getCelsius() {
        return celsius;
    }
}

Now invalid temperatures are rejected automatically. The internal representation is hidden - you could later change how temperature is stored internally (perhaps to Kelvin) without affecting code that uses the class.

This approach offers three key benefits: validation ensures data integrity, flexibility allows internal changes without breaking external code, and control lets you decide exactly what operations are permitted on your data.

Challenge

Easy

Let's build a Password management class that demonstrates information hiding by protecting sensitive data and enforcing security rules through controlled access.

You'll create two files to organize your code:

Password.java: Create a Password class that hides its internal data and controls how passwords can be set and accessed:
- A private password field (String) that stores the actual password
- A private minLength field (int) that defines the minimum acceptable password length
- A constructor that takes the minimum length requirement
- A setter setPassword(String password) that only accepts passwords meeting the minimum length requirement. If valid, store it and return true; if too short, don't change the password and return false
- A getter getMaskedPassword() that returns the password with all characters replaced by asterisks (*) - never expose the actual password!
- A method checkPassword(String attempt) that returns true if the attempt matches the stored password, false otherwise
- A getter getLength() that returns the length of the current password (or 0 if no password is set)
Main.java: Create a Password object with a minimum length of 6, then read two inputs: a password to set and an attempt to check. Print three lines:
- Set: true or Set: false (result of setting the password)
- Masked: ****** (the masked version of the password)
- Match: true or Match: false (result of checking the attempt)

You will receive two inputs: the password to set, and the password attempt to check.

Notice how the actual password is never directly accessible from outside the class - this is information hiding in action. The class controls exactly what information is revealed and how the password can be modified.

Cheat sheet

Information hiding restricts direct access to an object's internal data by using private fields combined with getters and setters.

Without information hiding, fields are exposed and can be set to invalid values:

public class Temperature {
    public double celsius;  // Exposed directly
}

Temperature t = new Temperature();
t.celsius = -500;  // Invalid value allowed

With information hiding, you control access and validate data:

public class Temperature {
    private double celsius;
    
    public void setCelsius(double celsius) {
        if (celsius >= -273.15) {
            this.celsius = celsius;
        }
    }
    
    public double getCelsius() {
        return celsius;
    }
}

Key benefits of information hiding:

Validation: Ensures data integrity by rejecting invalid values
Flexibility: Allows internal changes without affecting external code
Control: Lets you decide what operations are permitted on your data

Try it yourself

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        
        // Read the password to set
        String passwordToSet = scanner.nextLine();
        // Read the password attempt to check
        String passwordAttempt = scanner.nextLine();
        
        // TODO: Create a Password object with minimum length of 6
        
        // TODO: Set the password and print the result ("Set: true" or "Set: false")
        
        // TODO: Print the masked password ("Masked: ******")
        
        // TODO: Check the password attempt and print the result ("Match: true" or "Match: false")
        
    }
}