How to share the same behaviour in different classes

design-patternsinheritance

I have a class called Process, which is extended by some different process types called ProcessA, ProcessB, etc.

class Process{}

class ProcessA extends Process{}
class ProcessB extends Process{}
//...
class ProcessN extends Process{}

There is also another class related to the data of A, but not the Process. I call it TempA

Now ProcessA has a method called calculate(), and TempA needs to be calculated in the same way as ProcessA. As ProcessA extends Process (and Java doesn't allow multiple inheritance), I can't make an abstract class like AbstractA, and use the calculate() method to make these two classes (ProcessA and TempA) have same calculation method.

So how do I make these two classes have the same calculation behaviour/method without copy/paste-duplication of methods?

Best Answer

Favour composition over inheritance. If ProcessA and TempA have common behaviour, abstract that behaviour out into a separate class and have both ProcessA and TempA contain a member of that class. This is also good from a testing point of view, as it means you can separately unit test the common behaviour, and (if necessary) mock it out when testing ProcessA and TempA.

Related Solutions

Design Patterns – How to Use the Same Behaviour in Different Classes

The Strategy pattern is what I would use for this (encapsulating an algorithm). How the alignment is done is something that can be configured at runtime. There are also lots of different ways of aligning elements so you encapsulate them behind an interface. The example below is one way you could use strategy pattern with your Aligner class.

class Panel
{
    UIElement[] Children;
    IAligner Aligner;

    public SetAlignment(IAligner aligner)
    {
        this.Aligner = aligner;
    }

    public void Render()
    {
        Aligner.Align(Children)
        Display(Children)
    }
}

interface IAligner
{
    void Align(UIElement[] elements)
}

class LeftAligner : IAligner
class RightAligner: IAligner
class CenterAligner: IAligner

Design – How bad is it to have two methods with the same name but different signatures in two classes

These functions both have to do with collisions, but what they do is very different, so giving them names that more clearly describe what they actually do will make it easier for future developers to understand the difference without having to look at the logic inside.

The method that checks if the object is colliding with another object could be called checkForCollision.

The method that resolves collisions of the object with other objects could be called resolveCollisions or handleCollisions.

When two functions do almost the same thing is often the best time to give them more specific names to make their difference clear.

Best Answer

Related Solutions

Design Patterns – How to Use the Same Behaviour in Different Classes

Design – How bad is it to have two methods with the same name but different signatures in two classes

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