Java 中的类 getDeclaredAnnotationsByType()方法，示例
原文:https://www . geesforgeks . org/class-getdeclaredannotationbytype-method-in-Java-with-examples/
java.lang.Class 类 的getdeclaredannotationbytype()方法用于获取该类中存在的指定声明注释类型的声明注释。方法返回指定声明注释类型的声明注释数组。
语法:
public A[] getDeclaredAnnotationsByType(Class<T> declared annotationClass)
参数:该方法接受一个参数声明的注释类，它是要获取的声明注释的类型。
返回值:这个方法为指定的声明注释类型返回一个声明注释的数组。
*异常:*此方法抛出:
- *NullPointRexception:*如果给定的声明注释类为空。
下面的程序演示了 getDeclaredAnnotationsByType()方法。
*例 1:*
// Java program to demonstrate
// getDeclaredAnnotationsByType() 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 getDeclaredAnnotationsByType() method
System.out.println(
"DeclaredAnnotation of myClass of type DeclaredAnnotation: "
+ Arrays.toString(
myClass
.getDeclaredAnnotationsByType(
DeclaredAnnotation.class)));
}
}
*输出:*
由 myClass 表示的类:class Test DeclaredAnnotation 类型的 myClass 的 DeclaredAnnotation:[@ DeclaredAnnotation(key = GFG，value=GeeksForGeeks)]
*例 2:*
// Java program to demonstrate
// getDeclaredAnnotationsByType() 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 getDeclaredAnnotationsByType() method
System.out.println(
"DeclaredAnnotation of myClass of type Deprecated: "
+ Arrays.toString(
myClass
.getDeclaredAnnotationsByType(
Deprecated.class)));
}
catch (Exception e) {
System.out.println(e);
}
}
}
*输出:*
由 myClass 表示的类:class Test DeclaredAnnotation 类型的 myClass 已弃用:[@java.lang.Deprecated()]
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