What is a hook method?

Question

I am studying some design standards and came across this method, however, its concept was not clear to me.
What the method does and how it relates to the Template Method?
I’d like an example in java. Part I didn’t understand:

hook methods are methods that allow extension. The superclass has a public primary method that is invoked by its customers. This method delegates part of its execution to the hook method, which is an abstract method that must be implemented by the subclass...

Answer 1

These methods hook cited are used in the Template pattern. Just as the excerpt you quoted mentions, there is an abstract class A that delegates parts of its functionality to abstract methods. A concrete class B that inherits from this class need to implement these methods so that the code Compile. See an example:

public abstract class MinhaClasseAbstrata {
    public abstract int porcaoPersonalizada(String parametro);

    public int acaoPrincipal(String parametro) {
        return parametro.length() + porcaoPersonalizada(parametro);
    }
}

public MinhaClasseConcreta extends MinhaClasseAbstrata {

    public int porcaoPersonalizada(String parametro) {
        return parametro.length() + 55; // um cálculo qualquer específico para esse caso
    }

}


public MinhaOutraClasseConcreta extends MinhaClasseAbstrata {

    public int porcaoPersonalizada(String parametro) {
        return parametro.length() + 23; // um cálculo qualquer específico para esse caso
    }

}

That way, you know you can call acaoPersonalizada in any copy of the class MinhaClasseAbstrata that there will be a guaranteed return, based on the definition of porcaoPersonalizada of the specific type of the object in question.

Answer 2

The "Hook Method" acts as a placeholder within "Template Method".

This means that it is a method declared in the base class, but is only defined in the derived classes.

Take a closer look at this link, which explains about the Template Method Pattern: https://sourcemaking.com/design_patterns/template_method