使用新的Java 14 Record功能，是否可以为同一Re​​cord创建多个构造函数？

编程问答 2022-08-14

问题描述

我有很多使用Lombok的“数据”类，我想迁移所有这些类以使用Java 14中可用的新Record功能。借助新的Java 14 Record功能，是否可以为相同的记录？如果没有，还有其他选择吗？

解决方法

从Java 15开始（请参见JEP 384: Records (Second Preview)），您可能在记录中有多个构造函数。

但是，每个构造函数必须委托给记录的规范构造函数，该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");
    }
}
javajavarecordrecord