Java类实例管理：使用静态工厂方法追踪对象创建与维护唯一性

import java.util.ArrayList;

static public class Ship {
    // 存储船只名称，用于唯一性检查 (后续将被优化)
    private static ArrayList<String> ships = new ArrayList<String>();
    // 存储Ship对象本身
    private static ArrayList<Ship> shipObs = new ArrayList<Ship>();
    String name;
    private ArrayList<String> cruises = new ArrayList<String>();
    int maxPassengers;
    private static final String[] CABINS = new String[] {"Balcony", "Ocean View", "Suite", "Interior"};
    private int[] passengers = new int[] {0,0,0,0};
    boolean inService = false;

    public Ship(String name, int maxPassengers) {
        // 确保船只名称唯一性
        if (ships.size() == 0) {
            this.name = name;
            ships.add(name);
        } else {
            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; // 构造函数中过早返回
                }
            }
            this.name = name;
            ships.add(name);
        }
        this.maxPassengers = maxPassengers;
        // 尝试在此处添加this到shipObs，但可能不完整或存在逻辑问题
        // shipObs.add(this); // 无法直接在此处有效处理所有情况
    }
}

import java.util.ArrayList;

public final class Ship {

    // 存储Ship对象本身，现在直接用于唯一性检查
    private static final ArrayList<Ship> shipObs = new ArrayList<>();
    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;

    // 1. 将构造函数设为私有
    private Ship(String name, int maxPassengers) {
        this.name = name;
        this.maxPassengers = maxPassengers;
        // 构造函数只负责初始化，不进行复杂业务逻辑或集合添加
    }

    // 2. 提供一个静态工厂方法来创建Ship实例
    public static Ship createAShip(String name, int maxPassengers) {
        // 2.1 在创建前进行唯一性检查
        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
            }
        }

        // 2.2 如果名称唯一，则创建新对象
        Ship theShip = new Ship(name, maxPassengers);
        // 2.3 将新创建的对象添加到静态集合中
        shipObs.add(theShip);
        return theShip; // 返回新创建的对象
    }

    // 可以添加其他方法，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
    }

    // 示例：添加一个获取船只名称的方法
    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return "Ship{" +
               "name='" + name + '\'' +
               ", maxPassengers=" + maxPassengers +
               '}';
    }

    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: " + Ship.getAllShips());

        // 验证 ship1 和 ship3 是否是同一个对象
        System.out.println("Is ship1 the same as ship3? " + (ship1 == ship3));
    }
}