Code Smell 11 - Subclassification for Code Reuse

Code Smell 11 - Subclassification for Code Reuse

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Code reuse is good. But subclassing generates a static coupling.

TL;DR: Favor composition over inheritance. Always. Period.

Problems

  • Coupling

  • Maintainability

Solutions

  • Favor composition.

Exceptions

  • If hierarchy follows the principle behaves like then it is safe.

Sample Code

Wrong

public class Rectangle {

    int length;
    int width;

    public Rectangle(int length, int width){
        length = length;
        width = width;
    }

    public int area(){
        return length * width;
    }
}

public class Square extends Rectangle {

     public Square(int size){
        super(size, size); 
    }

    public int area(){
        return length * length;
    }
}

public class Box extends Rectangle{    

}
abstract public class Shape{

    abstract public int area();
}

public final class Rectangle extends Shape {

    int length;
    int width;

    public Rectangle(int length, int width){
        length = length;
        width = width;
    }

    public int area(){
        return length * width;
    }
}

public final class Square extends Shape {

     int size;

     public Square(int size){
        size = size; 
    }

    public int area(){
        return size * size;
    }
}

public final class Box {

    Square shape;

    public Box(int size){
        shape = new Square(size); 
    }

    public int area(){
        return shape.area();
    }
}

Detection

  • Overriding can issue warnings when subclassing concrete methods.
  • Deep Hierarchies (more than 3 levels) are also a clue of bad subclassing.

Tags

  • Composition

Conclusion

In legacy systems is very common to have Deep Hierarchies and method overriding, we need to refactor them and subclass by essential reasons and not implementative ones.

Relations

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Credits

Photo by Brandon Green on Unsplash


This article is part of the CodeSmell Series.

Last update: 2021/06/15

 
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