用示例将 getDeclaredAnnotation()方法打包到 Java 中
原文:https://www . geesforgeks . org/package-getdeclaredannotation-method-in-Java-with-examples/
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,如果该类中存在这样的声明注释。方法以对象的形式返回该类。
语法:
public T getDeclaredAnnotation(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:该方法返回声明的标注类的指定对象。
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 getDeclaredAnnotation()方法。
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:
由 myClass 表示的类:class Test DeclaredAnnotation of my class:@ DeclaredAnnotation(键=GFG,值=GeeksForGeeks)
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:
由 myClass 表示的类:class Test DeclaredAnnotation of my class:@ Java . lang .弃用()
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