Java AnnotatedElement isAnnotationPresent()用法及代码示例

java.lang.AnnotatedElement类的isAnnotationPresent()方法用于检查实现此接口的类中是否存在指定注释类型的注释。该方法返回一个声明相同的布尔值。

用法:

public boolean isAnnotationPresent(Class<T> annotationClass)

参数：此方法接受参数注释类，它是要获取的注释的类型。

返回值：此方法返回声明相同的布尔值。

异常：该方法抛出：

NullPointerException ：如果给定的注释类为null。

下面的程序演示了isAnnotationPresent()方法。

范例1：

// Java program to demonstrate 
// isAnnotationPresent() 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 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()); 
  
        // Check if there is any annotation 
        // using isAnnotationPresent() method 
        System.out.println( 
            "If there is any annotation"
            + " in myAnnotatedElement:"
            + myAnnotatedElement 
                  .isAnnotationPresent( 
                      Annotation.class)); 
    } 
}

输出：

AnnotatedElement represented by myAnnotatedElement:class Test
If there is any annotation in myAnnotatedElement:true

范例2：

// Java program to demonstrate 
// isAnnotationPresent() method 
  
import java.util.*; 
import java.lang.reflect.*; 
import java.lang.annotation.*; 
  
// Class with no annotations 
public class Test { 
  
    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 isAnnotationPresent() method 
        System.out.println( 
            "If there is any annotation"
            + " in myAnnotatedElement:"
            + myAnnotatedElement 
                  .isAnnotationPresent( 
                      Annotation.class)); 
    } 
}

输出：

AnnotatedElement represented by myAnnotatedElement:class Test
If there is any annotation in myAnnotatedElement:false

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

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注：本文由纯净天空筛选整理自guptayashgupta53大神的英文原创作品 AnnotatedElement isAnnotationPresent() method in Java with Examples。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。