how to design class method that returns two different return type?

Question

一个具有较小逻辑的子类，它返回布尔值true / false或错误消息，但在发生任何异常的情况下，它会陷入同一个类和错误消息中，仅是为了暗示上层类，该上层类曾在UI中显示错误消息。无法考虑如何管理子类的返回值，因为如果子类成功运行，则返回布尔值true / false，但是如果出错，则返回String错误消息，这一点我发现方法有两种不同类型的返回值问题。帮助我如何解决这个问题。

Answer 1

You have two options return an object

class Status {
   Boolean succesful;
   String errorText;
}

or throw an Exception if an error occurs

throw new Exception( errorText );

Answer 2

Why do you return String error code? Just throw your exception(maybe, wrapped in some other one) and receive it upper.

Answer 3

Your question is not very clear.
From my understanding, you should return a Boolean or an Exception.
You should set your error message in the exception (see: http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Exception.html#Exception%28java.lang.String%29 ). You can also return different exceptions if you need.

Answer 4

If you have your subclass return a variable of type Object you can check its data type higher up.

//Success
Object object = new Boolean();

//Fail
Object object = new String();

if(object instanceOf Boolean) {
//Do something
} else if(object instanceOf String) {
//Do something else
}

Answer 5

Consider using Functional Java's Either class. It is an implementation to hold one of two values.

Either