Java 入門進階：面向對象編程核心概念與租車系統實戰練習

學習路線圖

1. 類與對象：定義、構造、this、static、內部類
2. 封裝：訪問修飾符、包管理、Getter/Setter、驗證
3. 繼承：extends、方法重寫、super、final、Object 類
4. 多態：向上/向下轉型、instanceof、抽象類、接口、UML

綜合練習：控制台租車系統

需求：展示車型 → 選擇車輛/數量/天數 → 輸出總載客、載貨、總金額。

領域模型

abstract class Car { abstract int rentPerDay(); }
interface CarryPeople { int capacity(); }
interface CarryGoods { int loadKg(); }

class SmallCar extends Car implements CarryPeople {
    public int rentPerDay() { return 100; }
    public int capacity() { return 4; }
}
class Bus extends Car implements CarryPeople {
    public int rentPerDay() { return 500; }
    public int capacity() { return 30; }
}
class Pickup extends Car implements CarryPeople, CarryGoods {
    public int rentPerDay() { return 200; }
    public int capacity() { return 4; }
    public int loadKg() { return 200; }
}
class Truck extends Car implements CarryGoods {
    public int rentPerDay() { return 500; }
    public int loadKg() { return 2000; }
}

主程序邏輯

Scanner sc = new Scanner(System.in);
List rented = new ArrayList<>();
// 交互選擇車型、數量、天數...
int totalRent = rented.stream().mapToInt(Car::rentPerDay).sum() * days;
int totalPeople = rented.stream().filter(c -> c instanceof CarryPeople)
                        .mapToInt(c -> ((CarryPeople)c).capacity()).sum();
int totalLoad = rented.stream().filter(c -> c instanceof CarryGoods)
                      .mapToInt(c -> ((CarryGoods)c).loadKg()).sum();
System.out.printf("總租金: %d 元, 載客: %d 人, 載貨: %d kg%n", totalRent, totalPeople, totalLoad);

運行效果

通過該練習可熟練掌握繼承、接口、多態、集合流式操作等核心技能。