java - 我可以像参数一样引用子类吗？

Question

这个问题已经有答案了:

Create instance of generic type in Java? (29 个回答)

已关闭 4 年前。

我想在我的抽象类中引用任何潜在的子类，例如参数，以创建通用函数，例如，在不重载的情况下创建子类的新实例。

abstract class Fictional
{
  public static ArrayList<SUBCLASS_PARAM> subclassArray = new ArrayList<SUBCLASS_PARAM>();
  int i;

  private Fictional(int i) //All subclasses have to implement this constructor
  {
     this.i = i;
     //body
  }

  public static SUBCLASS_PARAM loadFromFile() //I wouldn't have to override this method
  {
     SUBCLASS_PARAM subclass = new SUBCLASS_PARAM(1); //it's not possible to make new instance of abstract class, but it would be possible with any other subclass
     subclassList.put(subclass);
     return subclass;
  }
}

class Real extends Fictional
{
//nothing here
}

class main
{
  Real r = Real.loadFromFile()
}

有什么办法可以制作这样的东西吗？

Answer 1

您可以使用泛型和子类来做到这一点，如下所示:

public abstract class Fictional<A extends Fictional> {
    public ArrayList<A> subclassArray = new ArrayList<A>();
    int i;

    public Fictional(int i) {
        this.i = i;
    }

    public A loadFromFile() //I wouldn't have to override this method
    {
        A subclass = this.build(1); //it's not possible to make new instance of abstract class, but it would be possible with any other subclass
        subclassList.put(subclass);
        return subclass;
    }

    protected abstract A build(int i);
}

class Real extends Fictional
{
    public Real(int i) {
        super(i);
    }

    @Override
    protected Fictional build(int i) {
        return new Real(i);
    }
}