Data class 特性

Kotlin 的 Data class 預設包含以下 Function：

建立 Data class

右鍵專案資料夾 → 「New」 → 「Kotlin Class/File」 → 命名並選擇 「Data class」

宣告

於 Data class 建構式宣告屬性，後續用於存取資料欄位

data class Country (
    val id: Int,
    val name: String, 
    val currency: String, 
    val region: String,
    val language: String
    ) {
    ...
}

若 Data class 僅具有資料欄位，無類別內容，可省略 {}

data class Country (
    val id: Int,
    val name: String, 
    val currency: String, 
    val region: String,
    val language: String
    )

Main Function 中呼叫 Data class 實體屬性及函式

建立物件實體

fun main() {
    val countryUk = Country(1, "United Kingdom", "GBP", "Europe", "English")
    val countryUs = Country(2, "United States", "USD", "North America", "English")
    val countryUk2 = Country(1, "United Kingdom", "GBP", "Europe", "English")

    //接續下方內容
}

toString()：將屬性資料轉換為字串

    //接續上方內容，寫於 main() function 中

    println(countryUk.toString()) 
    // output: Country(id=1, name=United Kingdom, currency=GBP, region=Europe, language=English)

equals()：判斷物件是否相等

    println(countryUk.equals(countryUk2)) 
    // output: true

copy()：複製為新的物件

    val countryUs2 = countryUs.copy()
    println(countryUs2) 
    // output: Country(id=2, name=United States, currency=USD, region=North America, language=English)

copy()：指定部份的屬性複製一個新的物件

    val countryUk3 = countryUk.copy(id = 3, name = "Canada", currency = "CAD")  
    println(countryUk3) 
    // output: Country(id=3, name=Canada, currency=CAD, "North America", "English")

componentN()：取得屬性值

    print(countryUk.component2())
    // output: United Kingdom

直接取得屬性值

    print(countryUs.name)
    // output: United States