How to use a simple data class in kotlin

Question

I am new to Kotlin and learning it, I am having a simple data class

data class Country{

    @SerializedName("name")
    val countryName: String?,
    @SerializedName("capital")
    val capital: String?,
    @SerializedName("flagPNG")
    val flag: String?

}

Errors I am facing:

enter image description here ]

Teetz · Accepted Answer · 2019-07-19 09:21:23Z

3

Your data class should look like this:

data class Country(

    @SerializedName("name")
    val countryName: String?,
    @SerializedName("capital")
    val capital: String?,
    @SerializedName("flagPNG")
    val flag: String?

)

The difference is, like mentioned in the comments: I used normal parentheses around the fields while you used curly braces

edited Jul 19, 2019 at 9:21

answered Jul 19, 2019 at 9:06

Teetz

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4 Comments

Devrath Over a year ago

it is working but, what is the difference ... both look the same .... waht mistake i made ?

Ahmed Hegazy Over a year ago

Data classes must have a primary constructor and that primary constructor needs to have at least one parameter!

pappbence96 Over a year ago

@Devrath look at how the answer uses normal parentheses around the fields while you used curly braces. Hard to notice at first.

Ravindra Pawar Over a year ago

Why it should have at least one parameter?

Jeel Vankhede · Accepted Answer · 2019-07-19 09:14:38Z

Data Class in Kotiln must have a variable/value parameter in it's constructor declaration.

Official doc states that :

To ensure consistency and meaningful behavior of the generated code, data classes have to fulfill the following requirements:

The primary constructor needs to have at least one parameter;

All primary constructor parameters need to be marked as val or var;

Data classes cannot be abstract, open, sealed or inner;

(before 1.1) Data classes may only implement interfaces.

So, your data class should be something similar like below :

data class Foo(
    val bar: Any
)

Note: In Kotlin, you can declare class constructor just by placing '()' following by class name to make it as primary constructor.

You class declaration should be something like below :

data class Country(
    @SerializedName("name")
    val countryName: String?,
    @SerializedName("capital")
    val capital: String?,
    @SerializedName("flagPNG")
    val flag: String?
)

Refer here for more info.

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