java - Child 类 Java 中的向下转型参数

Question

public class Contract extends StandardEntity {
/***/
@Composition
@OnDeleteInverse(DeletePolicy.UNLINK)
@OnDelete(DeletePolicy.CASCADE)
@OneToMany(mappedBy = "contract")
protected List<Objective> objectives;
/***/

是否可以将子类中的参数目标(ContractWthDeadLines扩展Contract)从List降级为List:

public class ObjectiveWitchDeadLine extends Objective

Answer 1

使您的 Contract 类通用

public class Contract<T extends Objective> extends StandardEntity {
   protected List<T> objectives;
}

如果你扩展它，你可以改变类型

public class ContractDeadline extends Contract<ObjectiveWitchDeadLine> {
}