Java - reduce code duplication - General coding question

Question

I'm looking for a way to reduce duplication in my code.

I have these 2 classes with same methods and ONLY difference private final House number; and private final NewHouse number; :

public class Building {

    private final UUID id;
    private final House number;
    private final HouseType houseType;

    Building(UUID Id, House number, HouseType houseType) {
        this.id = id;
        //....//
    }

    public House getNumber() {
        return number;
    }

    //get/set
    //other methods

}

public class NewBuilding {

    private final UUID id;
    private final NewHouse number;
    private final HouseType houseType;

    NewBuilding(UUID id, NewHouse number, HouseType houseType) {
        this.id = id;
        //....//
    }

    public NewHouse getNumber() {
        return number;
    }

    //get/set
    //other methods
}

Is there some way that I can combine this two classes in one and reduce duplication in my code?

Is there some design pattern that I can use? Should I create some 3rd class with common functionality?

This question should be on codereview.stackexchange.com not here. Please consider posting there. — Zohaib Amir
– Zohaib Amir, Commented Jul 24, 2019 at 11:46
Secondly, what is the difference between your House and NewHouse class? — Zohaib Amir
– Zohaib Amir, Commented Jul 24, 2019 at 11:53

Semyon Evgrafov · Accepted Answer · 2019-07-24 11:51:25Z

2

Just use parametrized types

public class Building<T> {

private final UUID id;
private final T number;
private final HouseType houseType;

Building(UUID Id, T number, HouseType houseType) {
    this.id = Id;
    this.number = number;
    this.houseType = houseType;
}

public T getNumber() {
    return number;
}

//get/set
//other methods

}

So you can use the following syntax

 Building<House> building = new Building<>(UUID.randomUUID(), new House(), new HouseType());
 Building<NewHouse> newHouse = new Building<>(UUID.randomUUID(), new NewHouse(), new HouseType());

answered Jul 24, 2019 at 11:51

Semyon Evgrafov

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1 Comment

Luis Iñesta Over a year ago

Also, if House and NewHouse share a common ancestor or interface (let's say IHouse), you'd better use Building<T extends IHouse> to restrict the accepted types.

Valijon · Accepted Answer · 2019-07-24 12:01:26Z

2

YES.

You can create single class with Generic Type + Inheritance extend new classes.

Let's say:

public class Structure<T> {

    private final UUID id;
    private final T number;
    private final HouseType houseType;

    Structure(UUID Id, T number, HouseType houseType) {
        this.id = id;
        //....//
    }

    public T getNumber() {
        return number;
    }

    //get/set
    //other methods
}

Your House class:

public class Building extends Structure<House> {

    //number attribute instanceof House 
    //get/set
    //other methods
}

Your NewHouse class:

public class NewBuilding extends Structure<NewHouse> {

    //number attribute instanceof NewHouse 
    //get/set
    //other methods

}

edited Jul 24, 2019 at 12:01

answered Jul 24, 2019 at 11:44

Valijon

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2 Comments

Luis Iñesta Over a year ago

Surely it's just a typo, but the constructor of Structure should be Structure, not Building

Valijon Over a year ago

Thanks. Copy + paste issue :-)

diginoise · Accepted Answer · 2019-07-24 11:45:48Z

0

Create third class which will be a parent to the 2 existing siblings:

public class GenericBuilding {
  private final UUID id;
  private final HouseType houseType;
  //...
}

public class Building extends GenericBuilding {
  private final House number;
  //...
}

public class NewBuilding extends GenericBuilding {
  private final NewHouse number;
  //...
}

answered Jul 24, 2019 at 11:45

diginoise

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Comments

swithen colaco · Accepted Answer · 2019-07-24 11:47:48Z

-3

You can create an Abstract class (say Construction) containing all the common variables and methods. Then have the two class Building and NewBuilding extend the Abstract class(Construction)

Link explaining abstraction

answered Jul 24, 2019 at 11:47

swithen colaco

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1 Comment

Zohaib Amir Over a year ago

If you create abstract class and exclude the House and NewHouse which are not common, what will rest of the functions do without these important variables? Your abstract class would have no implementation which would make it just like an interface. And even in that scenario code will be duplicated.

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