從 ZD52387880E1EA22817A72D3759218 訪問嵌套在伴侶 object 中的 Kotlin object

Question

我在 Kotlin 有這樣的結構

companion object Constants {
    /**
     * Collection of fields and values relative to phone books.
     */
    object PhoneBooks {
        /**
         * Field indicating the ID of a phone book.
         * Each phone book must have an unique ID.
         */
        const val PB_ID_KEY = "PB_ID"

        /**
         * Field indicating the status of phone book.
         */
        const val PB_STATUS_KEY = "PB_Status"

        /**
         * One of the possible [PB_STATUS_KEY] values, when the phone book is in indexing state
         * (usually at startup or in update phase).
         */
        const val PB_INDEXING = "Indexing"
        [...]

問題是我必須有可能從 Java 訪問子對象中的常量值，但這似乎不可能。 我怎樣才能在不改變結構的情況下解決這個問題？

Answer 1

JB Nizet評論道：

在這里工作正常

import static com.yourcompany.yourproject.YourClass.Constants.PhoneBooks;

接着

PhoneBooks.PB_ID_KEY

它對我很有用。 所以我認為讓它作為答案可見是有用的。

Answer 2

在上面的評論中，JB Nizet 展示了如何使用 static 導入來解決問題

但是查看提供的代碼我會使用枚舉

// kotlin
enum class PhoneBooks(val param:String) {
    PB_ID_KEY("PB_ID"),
    PB_STATUS_KEY("PB_Status"),
    PB_INDEXING("Indexing")

}

// java
System.out.println(PhoneBooks.PB_ID_KEY.getParam());

這里的一大優勢是代碼可讀性 PhoneBooks.PB_ID_KEY 以干凈的方式將 PB_ID_KEY 標記為電話簿常量

像 Kotlin 密封類一樣，kolin 編譯器為枚舉添加了一些很好的檢查（詳盡），它們旨在為模式匹配提供干凈可讀的代碼

請參閱@Rolands 在這里回答Kotlin: Using enums with when

Answer 3

嘗試使用界面:)

  companion object Constants {
/**
 * Collection of fields and values relative to phone books.
 */
interface PhoneBooks {
    /**
     * Field indicating the ID of a phone book.
     * Each phone book must have an unique ID.
     */
    const val PB_ID_KEY = "PB_ID"

    /**
     * Field indicating the status of phone book.
     */
    const val PB_STATUS_KEY = "PB_Status"

    /**
     * One of the possible [PB_STATUS_KEY] values, when the phone book is in indexing state
     * (usually at startup or in update phase).
     */
    const val PB_INDEXING = "Indexing"
    [...]