Template Method

The Template Method refers to a behavioral design pattern that outlines the basic structure of an algorithm within a base class, while allowing subclasses to modify certain steps of the algorithm without altering its overall structure.

Benefits of the Template Method Pattern

The Template Method pattern is useful when you have a series of steps in an algorithm, and the overall order of the steps should remain the same, but individual steps may need to be varied or extended in subclasses.

Problems Solved by the Template Method Pattern

The Template Method design pattern is particularly useful in the following scenarios:

1. Code Reusability and Reduction of Duplication: When different variations of an algorithm are required, the common steps can be implemented once in a base class and reused by different subclasses. This reduces code duplication.

2. Subclassing and Overriding: The pattern allows subclasses to redefine certain steps of an algorithm without changing the algorithm’s structure. This provides flexibility in the behavior of an algorithm.

3. Control over Subclasses: The pattern offers a way to enforce certain steps of an algorithm, by defining those steps in a base class method that cannot be overridden by subclasses.

4. Code Organization: The pattern provides a clear structure for complex algorithms, where each step is a separate method. This makes the code easier to understand and maintain.

For example, consider a software build process where the steps might include code validation, compilation, testing, and packaging. While the order of these steps would remain the same, the details of each step could vary based on the programming language or the specific project requirements. By using the Template Method pattern, you can define the overall structure of the build process in a base class and allow subclasses to provide their own implementation of each step.

--- Python example of a Template method implementation ---

 from abc import ABC, abstractmethod

 class AbstractTemplateClass(ABC):
     def template_method(self):
         self.base_operation1()
         self.required_operations1()
         self.base_operation2()
         self.hook1()
         self.required_operations2()
         self.base_operation3()
         self.hook2()

     def base_operation1(self):
         print("Base operation1")

     def base_operation2(self):
         print("Base operation2")

     def base_operation3(self):
         print("Base operation3")

     @abstractmethod
     def required_operations1(self):
         pass

     @abstractmethod
     def required_operations2(self):
         pass

     def hook1(self):
         pass

     def hook2(self):
         pass

 class ConcreteClass1(AbstractTemplateClass):
     def required_operations1(self):
         print("ConcreteClass1 says: Implemented Operation1")

     def required_operations2(self):
         print("ConcreteClass1 says: Implemented Operation2")

 class ConcreteClass2(AbstractTemplateClass):
     def required_operations1(self):
         print("ConcreteClass2 says: Implemented Operation1")

     def required_operations2(self):
         print("ConcreteClass2 says: Implemented Operation2")

     def hook1(self):
         print("ConcreteClass2 says: Overridden Hook1")

Here’s a simple example in Java:

abstract class AbstractTemplateClass {
    final void templateMethod() {
        baseOperation1();
        requiredOperation1();
        baseOperation2();
        hook1();
        requiredOperation2();
        baseOperation3();
        hook2();
    }

    void baseOperation1() {
        System.out.println("Base operation1");
    }

    void baseOperation2() {
        System.out.println("Base operation2");
    }

    void baseOperation3() {
        System.out.println("Base operation3");
    }

    abstract void requiredOperation1();

    abstract void requiredOperation2();

    void hook1() {}

    void hook2() {}
}

class ConcreteClass1 extends AbstractTemplateClass {
    @Override
    void requiredOperation1() {
        System.out.println("ConcreteClass1 says: Implemented Operation1");
    }

    @Override
    void requiredOperation2() {
        System.out.println("ConcreteClass1 says: Implemented Operation2");
    }
}

class ConcreteClass2 extends AbstractTemplateClass {
    @Override
    void requiredOperation1() {
        System.out.println("ConcreteClass2 says: Implemented Operation1");
    }

    @Override
    void requiredOperation2() {
        System.out.println("ConcreteClass2 says: Implemented Operation2");
    }

    @Override
    void hook1() {
        System.out.println("ConcreteClass2 says: Overridden Hook1");
    }
}

In this example, AbstractTemplateClass has a method called templateMethod() that contains a series of steps (methods). Some of these methods are implemented in AbstractTemplateClass (baseOperation1(), baseOperation2(), baseOperation3()) and some are abstract methods (requiredOperation1(), requiredOperation2()) that subclasses (ConcreteClass1, ConcreteClass2) are required to implement. The hook1() and hook2() methods are optional and can be overridden by subclasses if needed.