Java AnnotatedElement getDeclaredAnnotationsByType()用法及代碼示例

java.lang.AnnotatedElement類的getDeclaredAnnotations()方法用於獲取實現此接口的類中存在的指定聲明注釋類型的聲明注釋。該方法為指定的聲明的注釋類型返回聲明的注釋的數組。

用法:

public A[] getDeclaredAnnotationsByType(Class<T> declared annotationClass)

參數：此方法接受一個聲明的注釋類型的參數，該參數是要獲取的聲明注釋的類型。

返回值：此方法為指定的聲明的注釋類型返回聲明的注釋的數組。

異常：該方法拋出：

NullPointerException ：如果給定的聲明注釋類為null。

下麵的程序演示了getDeclaredAnnotationsByType()方法。

範例1：

// Java program to demonstrate 
// getDeclaredAnnotationsByType() method 
  
import java.util.*; 
import java.lang.reflect.*; 
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 myAnnotatedElement 
        AnnotatedElement myAnnotatedElement 
            = Test.class; 
  
        System.out.println( 
            "AnnotatedElement represented"
            + " by myAnnotatedElement:"
            + myAnnotatedElement.toString()); 
  
        // Get the declared annotation 
        // using getDeclaredAnnotationsByType() method 
        System.out.println( 
            "DeclaredAnnotation of myAnnotatedElement"
            + " of type DeclaredAnnotation:"
            + Arrays.toString( 
                  myAnnotatedElement 
                      .getDeclaredAnnotationsByType( 
                          DeclaredAnnotation.class))); 
    } 
}

輸出：

AnnotatedElement represented by myAnnotatedElement:class Test
DeclaredAnnotation of myAnnotatedElement of type DeclaredAnnotation:[@DeclaredAnnotation(key=GFG, value=GeeksForGeeks)]

範例2：

// Java program to demonstrate 
// getDeclaredAnnotationsByType() method 
  
import java.util.*; 
import java.lang.reflect.*; 
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 myAnnotatedElement 
            AnnotatedElement myAnnotatedElement 
                = Test.class; 
  
            System.out.println( 
                "AnnotatedElement represented"
                + " by myAnnotatedElement:"
                + myAnnotatedElement.toString()); 
  
            // Get the declared annotation 
            // using getDeclaredAnnotationsByType() method 
            System.out.println( 
                "DeclaredAnnotation of myAnnotatedElement"
                + " of type Deprecated:"
                + Arrays.toString( 
                      myAnnotatedElement 
                          .getDeclaredAnnotationsByType( 
                              Deprecated.class))); 
        } 
        catch (Exception e) { 
            System.out.println(e); 
        } 
    } 
}

輸出：

AnnotatedElement represented by myAnnotatedElement:class Test
DeclaredAnnotation of myAnnotatedElement of type Deprecated:[@java.lang.Deprecated()]

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

相關用法

注：本文由純淨天空篩選整理自guptayashgupta53大神的英文原創作品 AnnotatedElement getDeclaredAnnotationsByType() method in Java with Examples。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。