用示例在Java中封装 getDeclaredAnnotation() 方法
Java.lang.Package 类的getDeclaredAnnotation()方法用于获取指定声明注释类型的声明注释,如果此类声明的注释存在于此类中。该方法以对象的形式返回该类。
句法:
public T getDeclaredAnnotation(Class declared annotationClass)
参数:此方法接受一个参数声明的annotationClass ,它是要获取的声明注释的类型。
返回值:该方法返回声明的注解类的指定对象。
异常:此方法抛出:
- NullPointerException:如果给定的声明注释类为空。
下面的程序演示了 getDeclaredAnnotation() 方法。
示例 1:
// Java program to demonstrate
// getDeclaredAnnotation() 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 getDeclaredAnnotation() method
System.out.println(
"DeclaredAnnotation of myClass: "
+ myClass
.getDeclaredAnnotation(
DeclaredAnnotation.class));
}
}
输出:
Class represented by myClass: class Test
DeclaredAnnotation of myClass: @DeclaredAnnotation(key=GFG, value=GeeksForGeeks)
示例 2:
// Java program to demonstrate
// getDeclaredAnnotation() 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 getDeclaredAnnotation() method
System.out.println(
"DeclaredAnnotation of myClass: "
+ myClass
.getDeclaredAnnotation(
Deprecated.class));
}
catch (Exception e) {
System.out.println(e);
}
}
}
输出:
Class represented by myClass: class Test
DeclaredAnnotation of myClass: @java.lang.Deprecated()
参考: https://docs.oracle.com/javase/9/docs/api/ Java/lang/Package.html#getDeclaredAnnotation-java.lang.Class-