Java 继承。父母有父母的名单，孩子必须有孩子的名单。如何？

Question

我正在努力实现下一个：

家长：

public class Animal {
    private List<Animal> relatives;

    public List<Animal> getRelatives() {
        return relatives;
    }

    public void setRelatives(List<Animal> relatives) {
        this.relatives = relatives;
    }
}

孩子：

public class Dog extends Animal {
    private List<Dog> relatives;

    public List<Dog> getRelatives() {
        return relatives;
    }

    public void setRelatives(List<Dog> relatives) {
       this.relatives = relatives;
    }
}

但由于某种原因，我收到方法冲突的错误。这甚至可以通过继承而不使用泛型类型吗？

Answer 1

您实际上不需要覆盖/复制子类中的任何内容。

class Animal<Relative extends Animal<?>> {
  private List<? extends Relative> relatives;

  public List<? extends Relative> getRelatives() {
    return relatives;
  }

  public void setRelatives(List<? extends Relative> relatives) {
    this.relatives = relatives;
  }
}

class Dog extends Animal<Dog> {}

Answer 2

您可以在父类中使用泛型并持有relatives。此外，您应该注意持有意外修改：

public class Animal<T extends Animal<?>> {

    private final List<T> relatives = new ArrayList<>();

    public final List<T> getRelatives() {
        return relatives.isEmpty() ? Collections.emptyList() : Collections.unmodifiableList(relatives);
    }

    public final void addRelative(T relative) {
        Objects.requireNonNull(relative);
        relatives.add(relative);
    }
}

public class Dog extends Animal<Dog> {

    // just for test
    public List<Dog> getRelativesDogs() {
        return super.getRelatives();
    }

    // just for test
    public void addRelativeDog(Dog dog) {
        super.addRelative(dog);
    }

}