类类isAnnotationPresent()方法 (Class class isAnnotationPresent() method)

• isAnnotationPresent() method is available in java.lang package.

  isAnnotationPresent()方法在java.lang包中可用。

• isAnnotationPresent() method returns true when the annotation for the given type exists on this entity otherwise it returns false.

  当给定类型的注释存在于此实体上时， isAnnotationPresent()方法将返回true，否则将返回false。

• isAnnotationPresent() method is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.

  isAnnotationPresent()方法是一个非静态方法，仅可通过类对象访问，如果尝试使用类名访问该方法，则会收到错误消息。

• isAnnotationPresent() method: may throw an exception at the time checking present annotation.

  isAnnotationPresent()方法 ：在检查当前注释时可能会引发异常。

  NullPointerException: In this exception, when the given annotation class is null.

  NullPointerException ：在此异常中，当给定的注释类为null时。

Syntax:

句法：

    public boolean isAnnotationPresent(Class ann_class);

Parameter(s):

参数：

• Class ann_class – represents the Class object similar or correspondent to the annotation type.

  类ann_class –表示与注释类型相似或对应的Class对象。

Return value:

返回值：

The return type of this method is boolean, it returns a boolean value based on the following cases,

此方法的返回类型为boolean ，它基于以下情况返回布尔值：

• It returns true, when an annotation for the given type exists on this entity.

  当给定类型的注释存在于此实体上时，它返回true 。

• It returns false, when an annotation for the given type does not exists.

  当给定类型的注释不存在时，它返回false 。

Example:

例：

// Java program to demonstrate the example
// of boolean isAnnotationPresent(Class ann_class) method of Class
import java.security.*;
public class IsAnnotationPresentOfClass {public static void main(String[] args) throws Exception {Class ann1 = Identity.class;
Class ann2 = Deprecated.class;
// We are checking Annotation Present type of Deprecated
//class by using the method isAnnotationPresent()
boolean b1 = ann2.isAnnotationPresent(ann2);
System.out.println("is Deprecated an Annotation Present type" + " " + b1);
// We are checking Annotation Present type of Identity class
// by using the method isAnnotationPresent()
boolean b2 = ann1.isAnnotationPresent(ann1);
System.out.println("is Deprecated an Annotation Present type" + " " + b2);
}
}

Output

输出量

is Deprecated an Annotation Present type false
is Deprecated an Annotation Present type false

翻译自: https://www.includehelp.com/java/class-class-isannotationpresent-method-with-example.aspx