Java 中的类 getAnnotation()方法，带示例
原文:https://www . geesforgeks . org/class-getannotation-method-in-Java-with-examples/
java.lang.Class 类 的 getAnnotation() 方法用于获取指定注释类型的注释，如果该类中存在这样的注释。方法以对象的形式返回该类。
语法:
public T getAnnotation(Class<T> annotationClass)
参数:该方法接受一个参数标注类，即要获取的标注类型。
返回值:该方法返回标注类的指定对象。
异常:如果给定的注释类为空，该方法抛出:
- [null pointer exception: .
下面的程序演示了 getAnnotation()方法。
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)
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
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