Java中利用静态工厂方法管理对象实例与构造器最佳实践

import java.util.ArrayList;

public class Ship {
    private static ArrayList<Ship> allShips = new ArrayList<>(); // 存储所有Ship实例
    String name;
    int maxPassengers;

    public Ship(String name, int maxPassengers) {
        // 尝试在构造器中添加实例
        // allShips.add(this); // 此时this是有效的，但处理逻辑可能复杂
        this.name = name;
        this.maxPassengers = maxPassengers;

        // 原始问题中存在的重复名检查逻辑
        // if (allShips.contains(this)) { // 无法直接检查名称重复，因为此时allShips可能为空或不包含当前对象
        //     System.out.println("Ship " + name + " cannot be created because that name already exists");
        //     return; // 构造器中过早return是一个问题
        // }
    }
}

import java.util.ArrayList;

// 将类声明为final，进一步明确不允许继承，因为私有构造器已经阻止了外部继承
public final class Ship { 
    private static final ArrayList<Ship> shipObs = new ArrayList<>(); // 存储所有Ship实例
    String name;
    private ArrayList<String> cruises = new ArrayList<>();
    int maxPassengers;
    private static final String[] CABINS = {"Balcony", "Ocean View", "Suite", "Interior"};
    private int[] passengers = {0, 0, 0, 0};
    boolean inService = false;

    // 私有构造器，只能在类内部调用
    private Ship(String name, int maxPassengers) {
        this.name = name;
        this.maxPassengers = maxPassengers;
        // 注意：在这里不进行重复性检查，也不将this添加到shipObs
        // 构造器只负责初始化新创建对象的自身状态
    }

    // ... 其他方法
}

import java.util.ArrayList;

public final class Ship {

    private static final ArrayList<Ship> shipObs = new ArrayList<>();
    String name;
    private ArrayList<String> cruises = new ArrayList<>();
    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;

    // 私有构造器
    private Ship(String name, int maxPassengers) {
        this.name = name;
        this.maxPassengers = maxPassengers;
    }

    /**
     * 创建一个Ship实例。如果已存在同名Ship，则返回现有实例。
     * 否则，创建一个新实例并添加到管理列表中。
     *
     * @param name 船舶名称，必须唯一。
     * @param maxPassengers 船舶最大载客量。
     * @return 新创建或已存在的Ship实例。
     * @throws IllegalArgumentException 如果名称为空或无效。
     */
    public static Ship createAShip(String name, int maxPassengers) {
        // 1. 检查名称是否重复
        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; // 返回已存在的实例
            }
        }

        // 2. 如果名称不重复，创建新实例
        Ship theShip = new Ship(name, maxPassengers);
        // 3. 将新实例添加到管理列表
        shipObs.add(theShip);
        return theShip;
    }

    // 示例：获取所有船舶的方法
    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 class Main {
    public static void main(String[] args) {
        Ship ship1 = Ship.createAShip("Titanic", 2200);
        System.out.println("Created: " + ship1); // Created: Ship{name='Titanic', maxPassengers=2200}

        Ship ship2 = Ship.createAShip("Queen Mary 2", 2691);
        System.out.println("Created: " + ship2); // Created: Ship{name='Queen Mary 2', maxPassengers=2691}

        // 尝试创建同名船舶
        Ship ship3 = Ship.createAShip("Titanic", 2500); // Output: Ship Titanic cannot be created because that name already exists. Returning existing ship.
        System.out.println("Attempted to create duplicate, got: " + ship3); // Attempted to create duplicate, got: Ship{name='Titanic', maxPassengers=2200}

        // 验证 ship1 和 ship3 是同一个实例
        System.out.println("ship1 == ship3: " + (ship1 == ship3)); // ship1 == ship3: true

        System.out.println("All ships currently managed: " + Ship.getAllShips());
        // All ships currently managed: [Ship{name='Titanic', maxPassengers=2200}, Ship{name='Queen Mary 2', maxPassengers=2691}]
    }
}