将子类的集合作为超类的集合传递

Question

我有一个或多或少看起来像这样的 POJO：

public class Action {
    private String eventId;
    private List<ActionArgument> arguments;
    //action to perform when this action is done
    private List<Action> onCompleteActions;

    public Action() {
    }

    public Action(String eventId, List<ActionArgument> arguments, List<Action> onCompleteActions) {
        this.eventId = eventId;
        this.arguments = arguments;
        this.onCompleteActions = onCompleteActions;
    }

    public String getEventId() {
        return eventId;
    }
    public void setEventId(String eventId) {
        this.eventId = eventId;
    }
    public List<ActionArgument> getArguments() {
        return arguments;
    }
    public void setArguments(List<ActionArgument> arguments) {
        this.arguments = arguments;
    }
    public List<Action> getOnCompleteActions() {
        return onCompleteActions;
    }
    public void setOnCompleteAction(List<Action> onCompleteActions) {
        this.onCompleteActions = onCompleteActions;
    }
}

我有一个扩展类，如下所示：

public class UserDefinedAction extends Action {
    //for reordering actions with the default actions
    private String doBefore;
    private String doAfter;
    private String doAfterComplete;

    public String getDoBefore() {
        return doBefore;
    }

    public void setDoBefore(String doBefore) {
        this.doBefore = doBefore;
    }

    public String getDoAfter() {
        return doAfter;
    }

    public void setDoAfter(String doAfter) {
        this.doAfter = doAfter;
    }

    public String getDoAfterComplete() {
        return doAfterComplete;
    }

    public void setDoAfterComplete(String doAfterComplete) {
        this.doAfterComplete = doAfterComplete;
    }
}

在其他地方，我有一项服务，我想这样做：

...
UserDefinedAction udAction = new UserDefinedAction();
udAction.setOnCompleteAction(new ArrayList<UserDefinedAction>());

我认为这应该有效，因为是一个UserDefinedAction是Action因为它扩展了它吗？

Answer 1

List<UserDefinedAction> 不是List<Action>even if UserDefinedActionextends的子类Action。为了您可以将 a 传递List<UserDefinedAction>给您的服务，请将UserDefinedAction#setOnCompleteAction方法更改为接收 a List<? extends Action>，现在您可以将new ArrayList<UserDefinedAction>().

更多信息：

• 泛型：通配符