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Java Package getAnnotation()用法及代码示例


如果此Package中存在这样的注释,则使用java.lang.Package类的getAnnotation()方法来获取指定注释类型的注释。该方法以对象的形式返回该Package。

用法:

public T getAnnotation(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:此方法返回注释包的指定对象。

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getAnnotation()方法。

范例1:

// Java program to demonstrate 
// getAnnotation() method 
  
import java.util.*; 
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 class 
        Class myClass = Test.class; 
  
        System.out.println("Class represented by myClass:"
                           + myClass.toString()); 
  
        // Get the annotation 
        // using getAnnotation() method 
        System.out.println( 
            "Annotation of myClass:"
            + myClass.getAnnotation( 
                  Annotation.class)); 
    } 
}

输出:

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

范例2:

// Java program to demonstrate 
// getAnnotation() method 
  
import java.util.*; 
import java.lang.annotation.*; 
  
// Class with no annotations 
// getAnnotation() will return null 
public class Test { 
  
    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 annotation 
        // using getAnnotation() method 
        System.out.println( 
            "Annotation of myClass:"
            + myClass.getAnnotation( 
                  Annotation.class)); 
    } 
}

输出:

Class represented by myClass:class Test
Annotation of myClass:null

参考: https://docs.oracle.com/javase/9/docs/api/java/lang/Package.html#getAnnotation-java.lang.Class-



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