我如何根据公共标识符（java）实例化不同的子类

Question

I have a class for a tile.

public abstract class Tile {
    public Position pos;
    public char chr;
}

And many different classes that extend tile. Each subclass has its own identifier char. Now I have a function that receives a char and a position and needs to create and return a new instance of a tile subclass fitting the char in given position. Is there an elegant OOP way to do this other than run through all of the options?

Answer 1

So for me use of an identifier like this is a bit of a design flaw.

You could add something like the following to the abstract class:

public static Tile factory(char identifier, Position p) {
   Tile value = null;
   switch (identifier) {
      case `x`: {
        value = new XTile(p);
        break;
      }
      default {
        // throw an exception or provide a default
      }
   }
   return value
}

Effective Java (third edition) Item 21 "Prefer Class hierarchies to tagged classes" might provide an alternative to your design.