The Value field can be one of four different types - the best design?

Question

I have a class called "DataModel" or something that basically represents a unit of data, which can be either a string, or a number, or a date or a boolean with different (identical) attributes.

What is the best way to write this model?

• Enter a value of type Object

  interface DataModel {
     Object getValue();  // cast to whatever is needed
     int getValueType(); // uses four constants
  }
  

• They have four different implementations: "StringModel", "NumberModel", etc., each with its own method, "getValue ()". This means that if you have a DataModel, you will need to specify the correct model to get the value.

  interface DataModel {
     int getValueType();
  }
  interface NumberDataModel extends DataModel {
    Integer getValue();
  }
  ...
  

• There are four different methods, each of which throws an exception if caused by the wrong type of value:

  interface DataModel {
    String getStringValue();
    Integer getIntegerValue();
    ...
    int getValueType();
  }
  

• generics. , ... , IllegalStateException , T 4 ...

  interface DataModel<T> {
    T getValue();
  }
  

• . .;)

Answer 1

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Answer 2

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Answer 3

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Answer 4

4 - . .

, , 4 2. :

interface DataModel<T> {
   T getValue();
}
interface NumberDataModel extends DataModel<Number> {
   // empty
}
class NDM implements NumberDataModel {
   Number getValue() { return ... }
}

DataModel / .

Answer 5

As a universal alternative, you can use Class Literals as Runtime tokens and use newInstance()to get data instances with a security type. This allows you to check the compilation time using general parameters and check the runtime through isAssignableFrom().