Java コピーコンストラクタで安全にオブジェクトを複製する

import java.io.*;
import java.util.ArrayList;
import java.util.List;

public class CopyConstructorDemo {

    // ネストしたオブジェクト
    static class Address implements Serializable {
        private static final long serialVersionUID = 1L;
        String prefecture;
        String city;

        Address(String prefecture, String city) {
            this.prefecture = prefecture;
            this.city = city;
        }

        // コピーコンストラクタ
        Address(Address other) {
            this.prefecture = other.prefecture;
            this.city = other.city;
        }

        @Override
        public String toString() {
            return prefecture + " " + city;
        }
    }

    static class Employee implements Serializable {
        private static final long serialVersionUID = 1L;
        String name;
        int age;
        Address address;
        List<String> skills;

        Employee(String name, int age, Address address, List<String> skills) {
            this.name = name;
            this.age = age;
            this.address = address;
            this.skills = skills;
        }

        // コピーコンストラクタ: ネストも再帰的にコピー
        Employee(Employee other) {
            this.name = other.name;
            this.age = other.age;
            this.address = new Address(other.address);
            this.skills = new ArrayList<>(other.skills);
        }

        @Override
        public String toString() {
            return "Employee{name='" + name + "', age=" + age
                    + ", address=" + address + ", skills=" + skills + "}";
        }
    }

    // record + with パターン（Java 17+）
    record ImmutableAddress(String prefecture, String city) {}

    record ImmutableEmployee(String name, int age,
            ImmutableAddress address, List<String> skills) {
        ImmutableEmployee {
            skills = List.copyOf(skills); // 防御コピー
        }
        ImmutableEmployee withName(String newName) {
            return new ImmutableEmployee(newName, age, address, skills);
        }
        ImmutableEmployee withAddress(ImmutableAddress newAddr) {
            return new ImmutableEmployee(name, age, newAddr, skills);
        }
    }

    public static void main(String[] args) {
        // パターン 1: コピーコンストラクタ
        var original = new Employee("田中太郎", 30,
                new Address("東京都", "渋谷区"),
                new ArrayList<>(List.of("Java", "Python")));
        var copy = new Employee(original);
        copy.name = "鈴木次郎";
        copy.address.city = "新宿区";
        System.out.println("元（変化なし）: " + original);
        System.out.println("コピー:       " + copy);

        // パターン 2: record の with パターン
        var emp = new ImmutableEmployee("田中太郎", 30,
                new ImmutableAddress("東京都", "渋谷区"),
                List.of("Java", "Python"));
        var modified = emp.withName("鈴木次郎")
                .withAddress(new ImmutableAddress("大阪府", "梅田"));
        System.out.println("元: " + emp);
        System.out.println("変更後: " + modified);
    }
}