在 Java 中，创建自定义注解（annotation）是一个相对简单的过程。自定义注解可以用来为代码添加元数据，并在运行时通过反射进行处理。下面是创建自定义注解的基本步骤：
步骤

定义注解：使用 @interface 关键字定义自定义注解。可以指定注解的属性和元注解。

使用元注解：可以使用一些元注解来控制自定义注解的行为。例如，使用 @Retention 指定注解的保留策略，使用 @Target 指定注解可以应用的位置。

处理注解：使用反射机制读取和处理注解。

示例

下面是一个创建和使用自定义注解的完整示例：
1. 定义自定义注解

java

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

// 定义自定义注解
@Retention(RetentionPolicy.RUNTIME) // 注解在运行时可用
@Target(ElementType.METHOD) // 注解可以应用于方法
public @interface MyCustomAnnotation {
String value() default "default value"; // 属性，提供默认值
}

2. 使用自定义注解

java

public class MyClass {

    @MyCustomAnnotation(value = "Hello, World!")
    public void myMethod() {
        System.out.println("Executing myMethod");
    }
}

3. 处理自定义注解

java

import java.lang.reflect.Method;

public class AnnotationProcessor {
    public static void main(String[] args) throws Exception {
        MyClass myClass = new MyClass();
        Method method = myClass.getClass().getMethod("myMethod");

        // 检查方法是否有自定义注解
        if (method.isAnnotationPresent(MyCustomAnnotation.class)) {
            // 获取注解
            MyCustomAnnotation annotation = method.getAnnotation(MyCustomAnnotation.class);
            System.out.println("Annotation value: " + annotation.value());

            // 调用方法
            method.invoke(myClass);
        }
    }
}

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