How to Define Abstract Variables and Methods in Java?

How can I properly define abstract variables and methods in Java, ensuring that Eclipse prompts me to implement them in subclasses?

public abstract class clsAbstractTable {
    // Abstract variable without a modifier
    public static final String TABLENAME = null;  
    public abstract void init();
}

In Java, abstract classes are meant to define a base class that other classes can extend. When you want to enforce specific properties or behaviors in subclasses, you can define abstract variables (fields) and methods. However, Java does not allow abstract fields to have values assigned, and they can't be declared directly as abstract. Instead, you can implement a design that achieves your goal using a combination of abstract methods and static final variables.

public abstract class clsAbstractTable {
    public abstract String getTableName(); // Abstract method
    public abstract void init();
}

public class clsContactGroups extends clsAbstractTable {
    // Implementing the abstract method
    @Override
    public String getTableName() {
        return "contactgroups";
    }
    
    @Override
    public void init() {
        // Initialization code
    }
}

public class clsContacts extends clsAbstractTable {
    @Override
    public String getTableName() {
        return "contacts";
    }
    
    @Override
    public void init() {
        // Initialization code
    }
}

Causes

• Using the `abstract` modifier on variables (fields) is not allowed in Java.
• Wanting to ensure that subclasses provide their own implementation or value for certain variables.

Solutions

• Define abstract methods to be implemented in subclasses rather than abstract fields.
• Use static final fields with specific naming conventions and implement them in subclasses through static methods or directly within the class.

Mistake: Declaring abstract variables directly in the abstract class.

Solution: Use abstract methods instead to enforce subclasses to provide their own values.

Mistake: Forgetting to implement the abstract methods in subclasses, leading to compilation errors.

Solution: Ensure all subclasses implementing the abstract class include the required abstract methods.