Getter and Setter Methods

Part of the Object Oriented Programming section of Coddy's Java journey — lesson 11 of 87.

Getters and setters are methods that provide controlled access to private fields. A getter retrieves a field's value, while a setter modifies it.

The naming convention follows a standard pattern: prefix get or set followed by the field name with its first letter capitalized.

public class Product {
    private String name;
    private double price;
    
    // Getter for name
    public String getName() {
        return name;
    }
    
    // Setter for name
    public void setName(String name) {
        this.name = name;
    }
    
    // Getter for price
    public double getPrice() {
        return price;
    }
    
    // Setter with validation
    public void setPrice(double price) {
        if (price >= 0) {
            this.price = price;
        }
    }
}

The real power of setters is the ability to add validation logic. In the example above, setPrice only accepts non-negative values, protecting the object from invalid data.

For boolean fields, getters typically use the prefix is instead of get:

private boolean active;

public boolean isActive() {
    return active;
}

You can also create read-only fields by providing only a getter, or write-only fields by providing only a setter. This gives you fine-grained control over how external code interacts with your object's data.

Challenge

Easy

Let's build a Temperature converter that demonstrates the power of getters and setters with validation logic.

You'll create two files to organize your code:

Temperature.java: Define a Temperature class that stores a temperature value in Celsius. The class should have:
- A private celsius field (double)
- A private valid field (boolean) that tracks whether the temperature is physically possible
- A getter getCelsius() that returns the celsius value
- A setter setCelsius() that only accepts values at or above absolute zero (-273.15). If the value is valid, set valid to true; otherwise, don't change celsius and set valid to false
- A getter isValid() for the boolean field (remember: boolean getters use is prefix)
- A getter getFahrenheit() that converts and returns the temperature in Fahrenheit using the formula: (celsius * 9/5) + 32
Main.java: Create a Temperature object, read a celsius value as input, use the setter to set it, then print whether the temperature is valid and its Fahrenheit equivalent. Format your output as two lines:
- Valid: true or Valid: false
- Fahrenheit: X.X (showing one decimal place)

You will receive one input: a double value representing a temperature in Celsius.

For formatting the Fahrenheit output to one decimal place, you can use String.format("%.1f", value).

Cheat sheet

Getters and setters are methods that provide controlled access to private fields. A getter retrieves a field's value, while a setter modifies it.

The naming convention follows a standard pattern: prefix get or set followed by the field name with its first letter capitalized.

public class Product {
    private String name;
    private double price;
    
    // Getter for name
    public String getName() {
        return name;
    }
    
    // Setter for name
    public void setName(String name) {
        this.name = name;
    }
    
    // Getter for price
    public double getPrice() {
        return price;
    }
    
    // Setter with validation
    public void setPrice(double price) {
        if (price >= 0) {
            this.price = price;
        }
    }
}

Setters can include validation logic to protect objects from invalid data. In the example above, setPrice only accepts non-negative values.

For boolean fields, getters use the prefix is instead of get:

private boolean active;

public boolean isActive() {
    return active;
}

You can create read-only fields by providing only a getter, or write-only fields by providing only a setter.

Try it yourself

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double celsiusInput = scanner.nextDouble();
        
        // TODO: Create a Temperature object
        
        // TODO: Use the setter to set the celsius value
        
        // TODO: Print whether the temperature is valid (format: "Valid: true" or "Valid: false")
        
        // TODO: Print the Fahrenheit equivalent (format: "Fahrenheit: X.X")
        // Hint: Use String.format("%.1f", value) for one decimal place
    }
}