如何在不破坏依赖注入规则的情况下创建一个包含另一个类的元素列表的类？

Question

I have class that has several fields.

public class Foo {
 int firstCoef;
 int secondCoef;

 public Foo(String args){
  this.firstCoef=Integer.parseInt(args[0]);
  this.secondCoef=Integer.parseInt(args[1]);
 }
}

The arguments are assigned this way because I create several members of this class by reading data from .csv. I have another class that manages a list of Foo instances. It creates the whole list at once by reading it from file and uses the list for calculation. When creating a list in class constructor, it uses new Foo(string) .

public class FooManager {
    protected List<Foo> allFoos = new ArrayList<Foo>();

    public FooManager(List<String[]> input) {
        String[] line;
        for (int lineNumber = 0; lineNumber < input.size(); lineNumber++) {
            line = input.get(lineNumber);
            allFoos.add(new Foo(line));
        }
    }

    public int calculate(int number) {
        int result = 0;
        for (Foo foo : allFoos) {
            result += Math.pow(number + foo.getFirstCoef(), foo.getSecondCoef());
        }
        return result;
    }
}

From what I understand, this is considered bad design because the dependencies can't be injected. Also, it is hard to test. How could I change the design without complicating the input? The only goal of both classes is to be able to perform the calculation in the end.

Answer 1

You could add another layer, by adding a class that does the translation from the List to List:

public class FooParser implements Function<String[], Foo> {

    public Foo apply(String[] input) 
        for (int lineNumber = 0; lineNumber < input.size(); lineNumber++) {
            String[] line = input.get(lineNumber);
            allFoos.add(new Foo(line));
        }
    }
}

And then use it in the constructor of FooManger:

public FooManager(FooParser parser, List<String[]> input) {
    allFoos = parser.apply(input);
}

This way you have another part of logic in separate class - and it is easier to test in isolation.