kotlin - Kotlin 中的构建器模式

Question

我是 kotlin 世界的新手。我有一个用 Java 编写的现有构建器，并希望在将项目迁移到 Android 中的 kotlin 时将其转换为 Kotlin。但是，Android Studio 内置工具似乎有一些错误，则转换后的代码无法编译。它显示我的 UserBuilder 类中的变量无法访问。

这是来自 tutorial 的 Java 代码

public class Person {
    private final String firstName; // required
    private final String lastName; // required
    private final int age; // optional
    private final String phone; // optional
    private final String address; // optional

    private Person(UserBuilder builder) {
        this.firstName = builder.firstName;
        this.lastName = builder.lastName;
        this.age = builder.age;
        this.phone = builder.phone;
        this.address = builder.address;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public int getAge() {
        return age;
    }

    public String getPhone() {
        return phone;
    }

    public String getAddress() {
        return address;
    }

    public static class UserBuilder {
        private final String firstName;
        private final String lastName;
        private int age;
        private String phone;
        private String address;

        public UserBuilder(String firstName, String lastName) {
            this.firstName = firstName;
            this.lastName = lastName;
        }

        public UserBuilder age(int age) {
            this.age = age;
            return this;
        }

        public UserBuilder phone(String phone) {
            this.phone = phone;
            return this;
        }

        public UserBuilder address(String address) {
            this.address = address;
            return this;
        }

        public Person build() {
            return new Person(this);
        }

    }
}

自动转换的kotlin代码:

class Person private constructor(builder: UserBuilder) {
    val firstName: String // required
    val lastName: String // required
    val age: Int // optional
    val phone: String // optional
    val address: String // optional

    init {
        //cannot access the variables, they are private in UserBuilder
        this.firstName = builder.firstName  
        this.lastName = builder.lastName   
        this.age = builder.age
        this.phone = builder.phone
        this.address = builder.address
    }

    class UserBuilder(private val firstName: String, private val lastName: String) {
        private var age: Int = 0
        private var phone: String? = null
        private var address: String? = null

        fun age(age: Int): UserBuilder {
            this.age = age
            return this
        }

        fun phone(phone: String): UserBuilder {
            this.phone = phone
            return this
        }

        fun address(address: String): UserBuilder {
            this.address = address
            return this
        }

        fun build(): Person {
            return Person(this)
        }

    }
}

---

更新

class Person private constructor(builder: UserBuilder) {
    val firstName: String // required
    val lastName: String // required
    val age: Int // optional
    val phone: String? // optional
    val address: String? // optional

    init {
        this.firstName = builder.firstName
        this.lastName = builder.lastName
        this.age = builder.age
        this.phone = builder.phone
        this.address = builder.address
    }

    class UserBuilder(internal val firstName: String, internal val lastName: String) {
        internal var age: Int = 0
        internal var phone: String? = null
        internal var address: String? = null

        fun age(age: Int): UserBuilder {
            this.age = age
            return this
        }

        fun phone(phone: String): UserBuilder {
            this.phone = phone
            return this
        }

        fun address(address: String): UserBuilder {
            this.address = address
            return this
        }

        fun build(): Person {
            return Person(this)
        }

    }
}

Answer 1

鉴于它是 Kotlin，您实际上可以使用数据类使这变得简单得多。

data class User(val firstName: String, 
        val lastName: String,
        val age: Int = 0,
        val phone: String? = null,
        val address: String? = null)

就是这样!前两个参数是必需的，但如果要指定更多，只需按名称指定即可:

val user = User("John", "Doe", phone = "555-1212")

无需构建器!