How to Use Enums as Instance Variables in Java

What is the proper way to define and use enums as instance variables within a Java class?

public class Vehicle {
    public enum Type {
        CAR, MOTORCYCLE, TRUCK
    }

    private Type vehicleType;

    public Vehicle(Type vehicleType) {
        this.vehicleType = vehicleType;
    }

    public Type getVehicleType() {
        return vehicleType;
    }
}

Enums are a special data type in Java that enable a variable to be a set of predefined constants. This feature is particularly useful when working with instance variables in a class, allowing for type safety and improving code readability.

public class Vehicle {
    public enum Type {
        CAR, MOTORCYCLE, TRUCK;
        // method to get description
        public String getDescription() {
            switch (this) {
                case CAR: return "4 wheeled vehicle";
                case MOTORCYCLE: return "2 wheeled vehicle";
                case TRUCK: return "Vehicle for transporting goods";
                default: return "Unknown type";
            }
        }
    }

    private Type vehicleType;

    public Vehicle(Type vehicleType) {
        this.vehicleType = vehicleType;
    }

    public String getVehicleDescription() {
        return vehicleType.getDescription();
    }
}

Causes

• Lack of understanding about enums and how they can enhance class design.
• Not utilizing enum methods effectively, like `values()` or `valueOf()`, which can simplify object management.

Solutions

• Define your enum within the class or as a separate top-level class if it will be reused.
• Use the enum as a type for your instance variable, which helps in restricting the values and making the code less error-prone.
• Implement methods within the enum to provide additional functionality related to the type.

Mistake: Not defining enum values carefully, leading to confusion during development.

Solution: Clearly define each enum value and consider their meanings meticulously.

Mistake: Failing to use enum methods for added functionality.

Solution: Implement methods in the enum for utility functions related to its values.