Can You Pass Dynamic Values to Java Annotations?

Providing Dynamic Values to Java Annotations

Initial Attempt and Issue

In Java, you use annotations to provide metadata to classes, methods, and variables. In some scenarios, you may want to assign dynamic values to annotation attributes. However, assigning a non-constant expression, such as the result of a method call, to an annotation attribute is generally prohibited. As you experienced:

@MyInterface(aString = MyClass.GENERIC_GENERATED_NAME)

The compiler complains:

"The value for annotation attribute MyInterface.aString must be a constant expression"

Compiler Limitations

This limitation stems from the compiler's evaluation of annotation metadata for RetentionPolicy.RUNTIME annotations at compile time. The value assigned to the annotation attribute must be known at compile time.

Different Retention Policies

Java provides different retention policies for annotations:

• RetentionPolicy.SOURCE: Discarded after compile time
• RetentionPolicy.CLASS: Included in class files
• RetentionPolicy.RUNTIME: Retained throughout runtime

Resolution

Unfortunately, achieving your goal of providing dynamically-generated string values to annotations is not possible due to the compiler's limitations. Neither RetentionPolicy.SOURCE nor RetentionPolicy.RUNTIME allows for this.

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