How to create optional parameters for own annotations?

java annotations

Following is the annotation code

public @interface ColumnName {
   String value();
   String datatype();
 }

I would like to make datatype an optional parameter, for example

@ColumnName(value="password")

should be a valid code.

Steve Chambers

Seems like the first example in the official documentation says it all ...

/**
 * Describes the Request-For-Enhancement(RFE) that led
 * to the presence of the annotated API element.
 */
public @interface RequestForEnhancement {
    int    id();
    String synopsis();
    String engineer() default "[unassigned]"; 
    String date()     default "[unimplemented]"; 
}

i only looked at the tutorials.ie why i couldnt find this.may i know the difference between unassigned and unimplemented

There is not difference. They're just String values. They could be "peter" and "paul".

And what if my params are Class<?>s?

In that case, Java's type system still applies. For example Class<?> proxy() default Object.class

Thanks! The official documentation may have the example, but this SO post was the top hit on my Goggle search so your response and the link are helpful!

Johannes Wachter

To make it optional you can assign it a default value like that:

public @interface ColumnName {
   String value();
   String datatype() default "String";
 }

Then it doesn't need to be specified when using the Annotation.

How to create optional parameters for own annotations?

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