What is the differentiate amongst the final and abstract method in Java programming language

In the Java programming language, final methods and abstract methods represent two fundamentally different concepts that play important roles in class design and inheritance. Here are their main differences:

1. Purpose and Definition

• Final Methods: Methods marked with the final keyword cannot be overridden by subclasses. This is typically because the method's functionality is fully defined and stable, requiring no modifications or extensions. Using final methods ensures that the method's behavior remains unchanged, even within inheritance hierarchies.

  Example:

  java
  public class Vehicle {
      public final void startEngine() {
          System.out.println("Engine started");
      }
  }

• Abstract Methods: Abstract methods are declared without implementation and must be defined in abstract classes. Subclasses must override and implement these methods unless the subclass is also abstract. The purpose of abstract methods is to allow subclasses to provide specific implementation details, satisfying polymorphism requirements.

  Example:

  java
  public abstract class Animal {
      public abstract void makeSound();
  }
  
  public class Dog extends Animal {
      @Override
      public void makeSound() {
          System.out.println("Woof");
      }
  }

2. Impact on Inheritance

• Final Methods: Prevent methods from being modified by subclasses.
• Abstract Methods: Encourage subclasses to define concrete implementations, enhancing class flexibility and polymorphism.

3. Use Cases

• Final Methods: When you want the method to remain unmodified, or when the method contains critical security or consistency logic, using final methods is appropriate.
• Abstract Methods: When designing a base class that expects its subclasses to implement specific behaviors, abstract methods should be used.

4. Keyword Usage

• Final Methods: Use the final keyword.
• Abstract Methods: Use the abstract keyword, and it cannot be used with final.

In summary, final methods are used to prevent changes and maintain method consistency; while abstract methods provide a framework that must be implemented by subclasses, promoting polymorphism. Both are very useful in object-oriented design, but they have different goals and application scenarios.