类是 Java 中的 notationPresent()方法，带有示例
原文:https://www . geesforgeks . org/class-is notationpresent-method-in-Java-with-examples/
java.lang.Class 类 的is notationpresent()方法用于检查该类中是否存在指定注释类型的注释。方法返回一个表示相同内容的布尔值。
语法:
public boolean isAnnotationPresent(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:该方法返回布尔值表示相同。
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 isAnnotationPresent()方法。
例 1:
// Java program to demonstrate
// isAnnotationPresent() 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());
// Check if there is any annotation
// using isAnnotationPresent() method
System.out.println(
"If there is any annotation in myClass: "
+ myClass.isAnnotationPresent(
Annotation.class));
}
}
输出:
Class represented by myClass: class Test
If there is any annotation in myClass: true
例 2:
// Java program to demonstrate
// isAnnotationPresent() method
import java.util.*;
import java.lang.annotation.*;
// Class with no annotations
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 isAnnotationPresent() method
System.out.println(
"If there is any annotation in myClass: "
+ myClass.isAnnotationPresent(
Annotation.class));
}
}
输出:
Class represented by myClass: class Test
If there is any annotation in myClass: false
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