Java AnnotatedElement getAnnotationsByType()用法及代碼示例

java.lang.AnnotatedElement類的getAnnotationsByType()方法用於獲取實現此接口的類中存在的指定注釋類型的注釋。該方法返回指定注釋類型的注釋數組。

用法:

public A[] getAnnotationsByType(Class<T> annotationClass)

參數：此方法接受參數注釋類，它是要獲取的注釋的類型。

返回值：此方法返回指定注釋類型的注釋數組。

異常：該方法拋出：

NullPointerException ：如果給定的注釋類為null。

下麵的程序演示了getAnnotationsByType()方法。

範例1：

// Java program to demonstrate 
// getAnnotationsByType() method 
  
import java.util.*; 
import java.lang.reflect.*; 
import java.lang.annotation.*; 
  
// create a custom Annotation 
@Retention(RetentionPolicy.RUNTIME) 
@interface Annotation { 
  
    // This annotation has two attributes. 
    public String key(); 
  
    public String value(); 
} 
  
// call Annotation for method 
// and pass values for annotation 
@Annotation(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 annotation 
        // using getAnnotationsByType() method 
        System.out.println( 
            "Annotation of myAnnotatedElement"
            + " of type Annotation:"
            + Arrays.toString( 
                  myAnnotatedElement 
                      .getAnnotationsByType( 
                          Annotation.class))); 
    } 
}

輸出：

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

範例2：

// Java program to demonstrate 
// getAnnotationsByType() 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 annotation 
            // using getAnnotationsByType() method 
            System.out.println( 
                "Annotation of myAnnotatedElement"
                + " of type Deprecated:"
                + Arrays.toString( 
                      myAnnotatedElement 
                          .getAnnotationsByType( 
                              Deprecated.class))); 
        } 
        catch (Exception e) { 
            System.out.println(e); 
        } 
    } 
}

輸出：

AnnotatedElement represented by myAnnotatedElement:class Test
Annotation 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-

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