註釋參數 - 的String []類型的參數設置爲字符串字面

Question

閱讀How to set String Array in Java Annotation

我有一個查詢，爲下面的代碼：

@Unfinished("Just articleware") 
public @interface Unfinished { 
    public enum Priority {LOW, MEDIUM, HIGH} 
    String value(); 
    String[] owners() default ""; 
    Priority priority() default Priority.MEDIUM; 
} 

期待語法String[] owners() default {}。 Java編譯器如何允許字符串文字語法（""）爲String[]類型參數（owners）？

Answer 1

如註釋中所標記的，註釋密鑰owners的默認值""將創建一個數組，其元素爲空字符串。你也可以把一個字符串"default"在那裏，以及這將導致只是爲了如果需要爲空數組創建僅值「默認」的數組

OR

{}。

---

爲了測試這一點，你可以標記與運行時保留策略註解爲：

@Unfinished("Just articleware") 
@Retention(RetentionPolicy.RUNTIME) // mark with Runtime retention policy 
public @interface Unfinished { 
    enum Priority {LOW, MEDIUM, HIGH} 

    String value(); 

    String[] owners() default ""; 

    Priority priority() default Priority.MEDIUM; 
} 

註釋本

@Unfinished(value = "") 
public class AnnotatedClass { 

    public static void main(String[] args) { 
     System.out.println(""); 
    } 
} 

，然後使用反射來獲取的值的類Unfinished的密鑰爲：

public static void main(String[] args) throws Exception { 
    System.out.println("Testing..."); 
    Class<AnnotatedClass> obj = AnnotatedClass.class; 
    if (obj.isAnnotationPresent(Unfinished.class)) { 
     Annotation annotation = obj.getAnnotation(Unfinished.class); 
     Unfinished unfinished = (Unfinished) annotation; 
     System.out.println(Arrays.toString(unfinished.owners())); 
    } 
}