注解

Kotlin的注解依然源自于Java。

/**
 * 通用注解，既可以修饰类，也可以修饰方法和字段
 */
annotation class Universal(val value: String)

@Universal("Class")
class HelloWorld {
    @Universal("Field")
    val name = "lixingyun"

    @Universal("Method")
    fun hello() {
        println("lixingyun")
    }
}

/**
 * 自定义注解，实现API运行时的方法检查
 */
enum class MethodType {
    GET, POST
}

@Target(AnnotationTarget.CLASS)
@Retention(AnnotationRetention.RUNTIME)
annotation class HttpMethod(val type: MethodType)

interface HttpClient {
    val name: String
        get() = "/api"
    val version: String
        get() = "1.0.0"

}

@HttpMethod(MethodType.GET)
class HttpClientImpl : HttpClient {
}

fun geuUserInfo(client: HttpClient) {
    // 通过反射获取注解元信息
    val annotations = client.javaClass.annotations
    val annotation = annotations.find { it is HttpMethod } as? HttpMethod ?: return
    println(annotation?.type)
}

fun main() {
    // 应用注解
    val helloWorld = HelloWorld()
    helloWorld.hello()

    val client = HttpClientImpl()
    geuUserInfo(client)
}

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感谢支持

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