（翻译）

学习 Kotlin - Data Class

数据类

我们经常创建一个类来保存数据。在这样的类中，一些标准功能常常可以从数据中得到。在Kotlin中，这被称为数据类，并被标记为数据。

Example

在Java中

public class Developer {

    private String name;
    private int age;

    public Developer(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Developer developer = (Developer) o;

        if (age != developer.age) return false;
        return name != null ? name.equals(developer.name) : developer.name == null;

    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }

    @Override
    public String toString() {
        return "Developer{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

在 Kotlin 中

data class Developer(val name: String, val age: Int)

当我们将一个类标记为一个数据类时，您不必像在Java中那样实现或创建以下函数。

• hashCode()
• equals()
• toString()
• copy()

编译器会自动在内部创建这些代码，因此也会产生干净的代码。

虽然，数据类需要满足的需求很少:

• 主构造函数需要至少有一个参数。
• 所有主构造函数参数需要标记为val或var
• 数据类不能是抽象的、开放的、密封的或内部的。

因此，当您遇到这些情况时，请使用data class。

（原文）

Learn Kotlin - Data Class

Data Class

We frequently create a class to do nothing but hold data. In such a class some standard functionality is often mechanically derivable from the data. In Kotlin, this is called a data class and is marked as data.

Example

In Java

public class Developer {

    private String name;
    private int age;

    public Developer(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Developer developer = (Developer) o;

        if (age != developer.age) return false;
        return name != null ? name.equals(developer.name) : developer.name == null;

    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }

    @Override
    public String toString() {
        return "Developer{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

In Kotlin

data class Developer(val name: String, val age: Int)

When we mark a class as a data class, you don’t have to implement or create the following functions like we do in Java.

• hashCode()
• equals()
• toString()
• copy()

The compiler automatically create these internally, so it also leads to clean code.

Although, there are few requirements that data classes need to fulfil:

• 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.

So whenever you get these situations, use data class.

原文链接：https://blog.mindorks.com/learn-kotlin-data-class