Java类实例管理：使用私有构造器与静态工厂方法追踪对象

static public class Ship {
    // ... 其他字段
    private static ArrayList<Ship> shipObs = new ArrayList<Ship>(); // 存储Ship对象的静态列表
    String name;
    // ... 其他字段

    public Ship(String name, int maxPassengers) {
        // 检查名称唯一性并提前返回的逻辑
        if (ships.size() == 0) {
            this.name = name;
            ships.add(name); // 这里的ships是ArrayList<String>，不是Ship对象列表
        } else if (ships.size() >= 1) {
            for (int i = 0; i < ships.size(); i++) {
                if (ships.get(i).equals(name)) {
                    System.out.println("Ship " + name + " cannot be created because that name already exists");
                    return; // 问题所在：构造器中提前返回
                }
            }
            this.name = name;
            ships.add(name);
        }
        this.maxPassengers = maxPassengers;
        // shipObs.add(this); // 假设在这里添加，但如果提前返回则不会执行
    }
}

import java.util.ArrayList;

public final class Ship {

    private static final ArrayList<Ship> shipObs = new ArrayList<>(); // 存储所有Ship对象的静态列表
    String name;
    private final ArrayList<String> cruises = new ArrayList<>();
    int maxPassengers;
    private static final String[] CABINS =
          new String[]{"Balcony", "Ocean View", "Suite", "Interior"};
    private final int[] passengers = new int[]{0, 0, 0, 0};
    boolean inService = false;

    /**
     * 私有构造器，强制通过静态工厂方法创建Ship实例。
     * 构造器只负责初始化对象的内部状态，不包含复杂的业务逻辑。
     */
    private Ship(String name, int maxPassengers) {
        this.name = name;
        this.maxPassengers = maxPassengers;
        // 构造器中不执行复杂的验证或列表添加逻辑
    }

    /**
     * 静态工厂方法，用于创建并注册Ship实例。
     * 该方法负责名称唯一性检查、对象创建和实例追踪。
     *
     * @param name 船只名称
     * @param maxPassengers 最大载客量
     * @return 如果名称唯一，返回新创建的Ship对象；如果名称已存在，返回现有Ship对象。
     */
    public static Ship createAShip(String name, int maxPassengers) {
        // 1. 检查名称唯一性
        for (Ship existingShip : shipObs) {
            if (existingShip.name.equals(name)) {
                System.out.println("Ship " + name
                    + " cannot be created because that name already exists. Returning existing ship.");
                return existingShip; // 如果名称已存在，返回现有对象
            }
        }

        // 2. 如果名称唯一，创建新对象
        Ship theShip = new Ship(name, maxPassengers);

        // 3. 将完全初始化的对象添加到静态追踪列表
        shipObs.add(theShip);

        return theShip;
    }

    // 可以在这里添加其他方法，例如获取所有船只列表
    public static ArrayList<Ship> getAllShips() {
        return new ArrayList<>(shipObs); // 返回副本以防止外部修改
    }

    // ... 其他getter/setter方法或业务逻辑
    @Override
    public String toString() {
        return "Ship{" +
               "name='" + name + '\'' +
               ", maxPassengers=" + maxPassengers +
               '}';
    }

    public String getName() {
        return name;
    }
}

public class ShipManagement {
    public static void main(String[] args) {
        Ship ship1 = Ship.createAShip("Titanic", 2200);
        Ship ship2 = Ship.createAShip("Queen Mary 2", 2691);
        Ship ship3 = Ship.createAShip("Titanic", 2000); // 尝试创建同名船只

        System.out.println("All created ships:");
        for (Ship ship : Ship.getAllShips()) {
            System.out.println(ship);
        }
        // 输出：
        // Ship Titanic cannot be created because that name already exists. Returning existing ship.
        // All created ships:
        // Ship{name='Titanic', maxPassengers=2200}
        // Ship{name='Queen Mary 2', maxPassengers=2691}
    }
}