java - 使用新的 Java 14 Record 功能，是否可以为同一个 Record 创建多个构造函数？

Question

我有一堆使用 Lombok 的“数据”类，我想迁移所有这些类以使用 Java 14 中提供的新 Record 功能。使用新的 Java 14 Record 功能，是否可以为同一个 Record 创建多个构造函数？如果没有，是否有替代方案？

Answer 1

使用 Java 14，记录不能有多个构造函数(引用:Java 14 - JEP 359: Records (Preview))。
从 Java 15 和 16+ 开始，记录可能有多个构造函数 .
(参见 Java 15 - JEP 384: Records (Second Preview) 和 Java 16 - JEP 395: Records (Final) )。
但是，每个构造函数 必须委托(delegate)给记录的规范构造函数 可以明确定义或自动生成。
一个例子:

public record Person(
    String firstName,
    String lastName
) {
    // Compact canonical constructor:
    public Person {
        // Validations only; fields are assigned automatically.
        Objects.requireNonNull(firstName);
        Objects.requireNonNull(lastName);

        // An explicit fields assignment, like
        //   this.firstName = firstName;
        // would be a syntax error in compact-form canonical constructor
    }

    public Person(String lastName) {
        // Additional constructors MUST delegate to the canonical constructor,
        // either directly:
        this("John", lastName);
    }

    public Person() {
        // ... or indirectly:
        this("Doe");
    }
}

另一个例子:

public record Person(
    String firstName,
    String lastName
) {
    // Canonical constructor isn't defined in code, 
    // so it is generated implicitly by the compiler.

    public Person(String lastName) {
        // Additional constructors still MUST delegate to the canonical constructor!
        // This works: 
        this("John", lastName);

        // (Re-)Assigning fields here directly would be a compiler error:
        // this.lastName = lastName; // ERROR: Variable 'lastName' might already have been assigned to
    }

    public Person() {
        // Delegates to Person(String), which in turn delegates to the canonical constructor: 
        this("Doe");
    }
}