Kotlin data class 数据类用法

实验数据

{"code":1,"message":"成功","data":{"name":"周杰轮","gender":1}
}

kotlin数据类使用方便提供如下内部Api：

1. equals()/hashCode()对

2. toString()

3. componentN()按声明顺序与属性相对应的函数。

4. copy()功能

这里主要关注3，4，分别表示解构，和简单的对象浅拷贝实现 ，具体用法如下用例：

对于data类继承普通类之后，data类使用copy会与预期不符。

open class Person(val name: String? = "")
data class StuProJO(val gender: Int? = null) : Person(name = "")data class Normal(val name: String? = null, val age: Int = 18, var gender: Int? = 0)/*** 对于数据类Normal，copy方法执行符合预期。属于浅拷贝*/
fun main2(args: Array<String>) {//解构val (var1, var2, var3) = Normal("周杰轮", 18, 1)println("$var1 $var2 $var3")val normal2= Normal("周杰轮", 18, 2)//浅拷贝println(normal2.copy(name = "周杰轮2"))}//输出
//Normal(name=周杰轮, age=18, gender=1)
//Normal(name=周杰轮2, age=18, gender=1)/*** 继承方式结果与预期不符**/
fun main(args: Array<String>) {val temp = try {JsonParser.parseString(student) as JsonObject} catch (e: JsonParseException) {JsonObject()}val jsonObject = temp.takeIf { it.has("data") }val metaObject = jsonObject?.get("data")val metaData = metaObject.toString()var studentOB = GsonHelper.getClassFromJsonString(metaData, StuProJO::class.java)println(studentOB.toString())println(studentOB.name)printProjo(studentOB.copy(gender = 10000))}fun printProjo(person: Person) {print("打印 ${person} 继承的姓名：${person.name}")
}//输出
//StuProJO(gender=1)
//周杰轮
//打印 StuProJO(gender=10000) 继承的姓名：

上面copy()用例与预期不符原因根据官方提供说明：

data class User(val name: String = “”, val age: Int = 0)
使用该copy()函数复制对象，允许您更改其某些属性，同时保持其余属性不变。上面类的这个函数的实现User如下：
fun copy(name: String = this.name, age: Int = this.age) = User(name, age)

对于复杂copy()用例，建议自定义函数来处理

stackoverflow：相关用例 Kotlin data class copy method not deep copying all members

工具类

public class GsonHelper {private static Gson sGson;private GsonHelper() {}public static synchronized Gson getGsonInstance() {if (sGson == null) {sGson = new Gson();}return sGson;}private static <T> T fromJson(String json, Type typeOfT) {try {return getGsonInstance().fromJson(json, typeOfT);} catch (JsonSyntaxException e) {e.printStackTrace();}return null;}public static <T extends Object> T getClassFromJsonString(String data, Class<T> clazz) {return fromJson(data, clazz);}}

kotlin office data class