Java继承。父级有父级列表，子级必须有子级列表。如何？

Question

我正在努力实现下一个目标：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。这是否可以通过继承而不使用泛型类型来实现？

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

您可以使用泛型并保留relatives在父类中。此外，您应该注意保留意外的修改：

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);

    }

}