How do you define an abstract class?

An abstract class is a type of class in object-oriented programming that cannot be instantiated, meaning you cannot create an object from it directly. Instead, other classes must inherit from the abstract class. Here are the steps to define an abstract class:

1. Declare the class using the keyword abstract. This keyword indicates that the class is abstract.

public abstract class AbstractClass {
    // class body
}

2. Inside the abstract class, you can define abstract methods and non-abstract methods. Abstract methods are declared without an implementation.

public abstract class AbstractClass {
    public abstract void abstractMethod(); // Abstract method

    public void nonAbstractMethod() { // Non-abstract method
        // method body
    }
}

3. Abstract methods do not have a body and are marked with the keyword abstract.

4. Subclasses of the abstract class must provide implementations for the abstract methods.

public class SubClass extends AbstractClass {
    public void abstractMethod() {
        // method body
    }
}

5. You can also have non-abstract methods in an abstract class, which can have a default implementation or can be overridden by the subclass if needed.

Remember, you cannot create an instance of an abstract class. Its purpose is to be extended by other classes.