用示例在Java中封装 isAnnotationPresent() 方法

Java.lang.Package 类的isAnnotationPresent()方法用于检查该类中是否存在指定注解类型的注解。该方法返回一个以相同开头的布尔值。

句法：

public boolean isAnnotationPresent(Class annotationClass)

参数：这个方法接受一个参数annotationClass ，它是要获取的注解的类型。
返回值：此方法返回以相同开头的布尔值。
异常：此方法抛出：

• NullPointerException：如果给定的注释类为空。

下面的程序演示了 isAnnotationPresent() 方法。
示例 1：

Java

// 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 
 

示例 2：

Java

// 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 
 

参考： https://docs.oracle.com/javase/9/docs/api/ Java/lang/Package.html#isAnnotationPresent-java.lang.Class-