Welcome back! In this course, we delve into Class Attributes and Methods in Java. These define an object's properties and behaviors. Our goal is to master the definition and application of these within a class. Through the construction of a CellPhone class, we will navigate this exciting journey!

Class attributes symbolize an object's properties. For instance, the attributes of a CellPhone might be its brand and model:

public class CellPhone {
    public String brand; // Brand of the phone
    public String model; // Model of the phone
}

Sometimes, attributes remain constant after initial set-up. The final keyword aids in creating such attributes. Let's add a chargerType attribute, which will be constant:

public class CellPhone {
    public String brand;
    public String model;
    public final String chargerType = "Type-C"; // A constant attribute
}

Methods are a class's behaviors, while attributes are its properties. For our CellPhone, a callDial method might be used to start a phone call:

public class CellPhone {
    public String brand = "iPhone";
    public String model = "15 Pro Max";
    public final String chargerType = "Type-C";

    public void callDial(String phoneNumber) {
        // Calling the given phone number, including class attributes
        System.out.println("Dialing " + phoneNumber + " from my " + brand + " " + model);
    }
}

Just as we humans can perform various tasks, our objects can possess more than one method. For instance, let's add another method, hangUp:

public void hangUp() {
    // Call has ended
    System.out.println("Call ended.");
}

To run this code, we can instantiate a class and call a method for the created instance:

CellPhone cellPhone = new CellPhone();
cellPhone.callDial("+1-212-456-7890"); // Prints: Dialing +1-212-456-7890 from my iPhone 15 Pro Max
cellPhone.hangUp(); // Prints: Call ended.

Methods can interact with and modify class attributes. This can be illustrated with an updateModel method that updates the model:

public void updateModel(String newModel) {
    // Updating the model attribute
    this.model = newModel;
    System.out.println("Model updated to " + newModel);
}

Here, the this keyword refers to the current instance of the class object. It means that we are setting the model field in the current CellPhone class object to newModel.