如果存在这样的注释,则使用Constructor类的getAnnotation()方法为指定的类型获取此构造函数对象注释,否则为null。指定的类型作为参数传递。
用法:
public <T extends Annotation> T getAnnotation(Class<T> annotationClass)
参数:此方法接受单个参数注解类,该参数表示与注解类型相对应的Class对象。
返回值:如果此元素上存在指定的注释类型,则此方法返回该元素的注释,否则返回null。
异常:如果给定的注释类为null,则此方法引发NullPointerException。
以下示例程序旨在说明getAnnotation()方法:
示例1:
// Java program to demonstrate
// Constructor.getAnnotation() method
import java.lang.annotation.Annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.AnnotatedType;
import java.lang.reflect.Constructor;
public class GFG {
public static void main(String... args)
throws NoSuchMethodException
{
// Create Constructor Object
Constructor[] constructors
= Demo.class.getConstructors();
// Create annotation object
Annotation annotation
= constructors[0]
.getAnnotation(PathVar.class);
if (annotation instanceof PathVar) {
PathVar customAnnotation
= (PathVar)annotation;
System.out.println(
"Path: "
+ customAnnotation.Path());
}
}
}
// Demo class
class Demo {
public Demo(@PathVar(Path = "Demo/usr")
String str) {}
}
// PathVar interface
@Target({ ElementType.TYPE_USE })
@Retention(RetentionPolicy.RUNTIME)
@interface PathVar {
public String Path();
}
输出:
Path: Demo/usr
示例2:
// Java program to demonstrate
// Constructor.getAnnotation() method
import java.lang.annotation.Annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Constructor;
public class GFG {
public static void main(String... args)
throws NoSuchMethodException
{
// Create Constructor Object
Constructor[] constructors
= Maths.class.getConstructors();
// Create annotation object
Annotation annotation
= constructors[0]
.getAnnotation(Calculator.class);
System.out.println(
"Annotation:"
+ annotation.toString());
}
}
// Demo class
@Calculator(add = "Adding value",
subtract = "Subtracting Value")
class Maths {
@Calculator(add = "Adding value",
subtract = "Subtracting Value")
public Maths() {}
}
// Calculator interface
@Retention(RetentionPolicy.RUNTIME)
@interface Calculator {
public String add();
public String subtract();
}
输出:
Annotation : @Calculator(add=Adding value, subtract=Subtracting Value)
参考:https://docs.oracle.com/javase/10/docs/api/java/lang/reflect/Constructor.html#getAnnotation(java.lang.Class)
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注:本文由纯净天空筛选整理自AmanSingh2210大神的英文原创作品 Constructor getAnnotation() method in Java with Examples。非经特殊声明,原始代码版权归原作者所有,本译文未经允许或授权,请勿转载或复制。