有了新的Java14记录功能，是否可以为同一记录创建多个构造函数？

Question

我有一大堆使用Lombok的“数据”类，我想将它们全部迁移到Java 14中提供的新记录功能。有了新的Java14记录功能，是否可以为同一记录创建多个构造函数？如果没有，还有其他选择吗

Answer 1

在Java14中，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。 （见Java 15 - JEP 384: Records (Second Preview)和Java 16 - JEP 395: Records (Final)）

但是，每个构造函数都必须委托给记录的规范构造函数，该构造函数可以显式定义或自动生成

举个例子：

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");
    }
}