Java Class getDeclaredAnnotations()用法及代碼示例

java.lang.Class類的getDeclaredAnnotations()方法用於獲取該類中存在的已聲明注釋。該方法返回存在的已聲明注釋的數組。

用法:

public DeclaredAnnotation[] getDeclaredAnnotations()

參數：此方法不接受任何參數。

返回值：此方法返回存在的已聲明注釋的數組。

下麵的程序演示了getDeclaredAnnotations()方法。

範例1：

// Java program to demonstrate 
// getDeclaredAnnotations() method 
  
import java.util.*; 
import java.lang.annotation.*; 
  
@Deprecated
public class Test { 
  
    public Object obj; 
  
    public static void main(String[] args) 
        throws ClassNotFoundException 
    { 
        try { 
            // returns the Class object for this class 
            Class myClass = Test.class; 
  
            System.out.println( 
                "Class represented by myClass:"
                + myClass.toString()); 
  
            // Get the declared annotation 
            // using getDeclaredAnnotations() method 
            System.out.println( 
                "DeclaredAnnotation of myClass:"
                + Arrays.toString( 
                      myClass.getDeclaredAnnotations())); 
        } 
        catch (Exception e) { 
            System.out.println(e); 
        } 
    } 
}

輸出：

Class represented by myClass:class Test
DeclaredAnnotation of myClass:[@java.lang.Deprecated()]

範例2：

// Java program to demonstrate 
// getDeclaredAnnotations() method 
  
import java.util.*; 
import java.lang.annotation.*; 
  
// create a custom DeclaredAnnotation 
@Retention(RetentionPolicy.RUNTIME) 
@interface DeclaredAnnotation { 
  
    // This declared annotation has two attributes. 
    public String key(); 
  
    public String value(); 
} 
  
// call DeclaredAnnotation for method 
// and pass values for declared annotation 
@DeclaredAnnotation(key = "GFG", value = "GeeksForGeeks") 
public class Test { 
  
    public Object obj; 
  
    public static void main(String[] args) 
        throws ClassNotFoundException 
    { 
  
        // returns the Class object for this class 
        Class myClass = Test.class; 
  
        System.out.println( 
            "Class represented by myClass:"
            + myClass.toString()); 
  
        // Get the declared annotation 
        // using getDeclaredAnnotations() method 
        System.out.println( 
            "DeclaredAnnotation of myClass:"
            + Arrays.toString( 
                  myClass.getDeclaredAnnotations())); 
    } 
}

輸出：

Class represented by myClass:class Test
DeclaredAnnotation of myClass:[@DeclaredAnnotation(key=GFG, value=GeeksForGeeks)]

參考： https://docs.oracle.com/javase/9/docs/api/java/lang/Class.html#getDeclaredAnnotations-

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