如何从常量 java 为注解提供值
我认为这在 Java 中可能是不可能的，因为注解及其参数是在编译时解析的.我有一个界面如下，
I am thinking this may not be possible in Java because annotation and its parameters are resolved at compile time. I have an interface as follows,
public interface FieldValues {
String[] FIELD1 = new String[]{"value1", "value2"};
}
和另一个类，
@SomeAnnotation(locations = {"value1", "value2"})
public class MyClass {
....
}
我用注释标记了许多类，我想知道是否可以避免在我更喜欢使用的每个注释中指定字符串
I mark many classes with the annotation and I would like to know if I can avoid specifying the strings in every annotation I would instead prefer to use
@SomeAnnotation(locations = FieldValues.FIELD1)
public class MyClass {
....
}
但是这会产生编译错误，例如注释值应该是数组初始化器等.有人知道我如何使用 String 常量或 String[] 常量来为注释提供值吗?
However this gives compilation errors like annotation value should be an array initializer etc. Does someone know how I can use a String constant or String[] constant to supply value to an annotation?
推荐答案
编译常量只能是原语和字符串:
15.28.常量表达式
编译时常量表达式是一个表达式，表示原始类型的值或不会突然完成且仅使用以下内容组成的字符串:
A compile-time constant expression is an expression denoting a value of primitive type or a String that does not complete abruptly and is composed using only the following:
- 原始类型的文字和
String 类型的文字 - 转换为原始类型并转换为
String - [...] 运算符 [...]
- 带括号的表达式，其包含的表达式是常量表达式.
- 引用常量变量的简单名称.
- TypeName 形式的限定名称.标识符表示常量变量.
- Literals of primitive type and literals of type
String - Casts to primitive types and casts to type
String - [...] operators [...]
- Parenthesized expressions whose contained expression is a constant expression.
- Simple names that refer to constant variables.
- Qualified names of the form TypeName . Identifier that refer to constant variables.
实际上在java中没有办法保护数组中的项目.在运行时，总是有人可以执行 FieldValues.FIELD1[0]=value3"，因此如果我们更深入地观察，数组不可能是真正的常量.
Actually in java there is no way to protect items in an array. At runtime someone can always do FieldValues.FIELD1[0]="value3", therefore the array cannot be really constant if we look deeper.
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