我是java新手（兩周前開始），我一直在做一些我在互聯網上發現的隨機挑戰。我當前的問題是，當我在我的任何子類（平板電腦和筆記本電腦）中訪問覆寫方法時，這使用了我給超類（設備）的引數，甚至在我宣告該類的新物件之前。
代碼運行良好，沒有任何語法錯誤，但顯然存在邏輯錯誤，因為子類回傳與父類相同的輸出，即使使用不同的引數，3 始終給出相同的輸出。我做了一些測驗，改變了一些東西，發現當我呼叫子類方法時，并沒有呼叫子類中被覆寫的方法，總是參考父類中的方法，并且不知道為什么，編輯器（我使用 VS Code）回傳參考設備類的訊息，從不參考子類方法。
但是，當我使用方法.getClass()和.getSimpleName()時，指的是子類，只有那些不起作用的方法。
它的代碼是：
- 我在App類中傳遞引數，在這里我初始化所有代碼并給出我的問題的引數：
public class App {
// It's the class that run all the code, it's suppose to run "the tests"
public static void main(String[] args) throws Exception {
Device[] devices = new Device[3];
devices[0] = new Tablet();
devices[1] = new Laptop((byte) 3, 500,'E', 250);
devices[2] = new Device((byte) 3, 600, 'D');
TotalPrice answer = new TotalPrice(devices);
answer.print_totals();
// Output I obtain:
// Total price of Devices: 700.0
// Total price of Laptops: 700.0
// Total price of Tablets: 700.0
// Output It's supposed to obtain, if the code works:
// Total price of Devices: 700.0
// Total price of Laptops: 580.0
// Total price of Tablets: 110.0
}
}
- 父類，設備：
import java.util.HashMap;
public class Device {
// The class parent, set the values for the "devices" and calculate the cost of each
// one
static float price, basis_price = 100f;
static byte weight, basis_weight = 1;
static char consumption_w, basis_consumption_w = 'F';
Device() {
weight = basis_weight;
price = basis_price;
consumption_w = basis_consumption_w;
}
Device(byte a_weight, float a_price) {
weight = a_weight;
price = a_price;
consumption_w = basis_consumption_w;
}
Device(byte a_weight, float a_price, char a_consumption_w) {
weight = a_weight;
price = a_price;
consumption_w = a_consumption_w;
}
static float calc_consume_w() {
// Calculate the wats consumed by the device and set the cost based on this
HashMap<Character,Float> cost_w = new HashMap<Character,Float>();
cost_w.put('A', 100f); cost_w.put('B', 80f); cost_w.put('C', 60f);
cost_w.put('D', 50f); cost_w.put('E', 30f); cost_w.put('F', 10f);
return cost_w.get(Character.toUpperCase(consumption_w));
}
public float calc_price() {
// Calculates the total cost of the Device, based on initial price, weight and
// wats consumed
float cost_w = calc_consume_w(),
cost_weight = weight > 1 && weight <= 2? 10f:
weight > 2 && weight <= 3? 50f:
weight >3 && weight <= 4? 80f:
weight > 4? 100f: 0;
return price cost_w cost_weight;
}
}
- Device, Laptop 的第一個子類和子類：
public class Laptop extends Device {
// Same as Device, just a more specific Device
// This need the argument "Hard Disk (hd)" to add more mone to the price
static float hd, basis_hd = 250;
Laptop () {
hd = basis_hd;
}
Laptop(byte a_weight, float a_price) {
hd = basis_hd;
weight = a_weight;
price = a_price;
}
Laptop(byte a_weight, float a_price, char a_consumption_w, float a_hd) {
hd = a_hd;
weight = a_weight;
price = a_price;
consumption_w = a_consumption_w;
}
public float calc_price() {
// This it's suppose to be a overridden method for the original in Device
// Make the same thing, just that add the value for Hard Disk
float cost_w = calc_consume_w(),
cost_weight = weight > 4? 100f:
weight > 3? 80f:
weight > 2? 50f:
weight > 1? 10f: 0,
cost_hd = hd > 1000? 100f:
hd > 500? 50f:
hd > 250? 10f: 0;
return price cost_w cost_weight cost_hd;
}
}
- Device，Tablet 的第二個子類和子類：
public class Tablet extends Device {
// Same as Device, just add the variable ram to add more money to the price
static float ram, basis_ram = 1;
Tablet() {
ram = basis_ram;
weight = basis_weight;
}
Tablet(byte a_weight, float a_price) {
ram = basis_ram;
weight = a_weight;
price = a_price;
}
Tablet(byte a_weight, float a_price, char a_consumption_w, float a_ram) {
ram = a_ram;
weight = a_weight;
price = a_price;
consumption_w = a_consumption_w;
}
public float calc_price() {
// The supposed overridden method of Device,
// Make the same, just add more value for ram
float cost_w = calc_consume_w(),
cost_weight = weight > 4? 100:
weight > 3? 80:
weight > 2? 50:
weight > 1? 10: 0,
cost_ram = ram > 4? 50:
ram > 2? 25:
ram > 1? 5: 0;
return price cost_w cost_weight cost_ram;
}
}
- 執行輸出的類 TotalPrice：
public class TotalPrice {
// This class it's the last class to be summoned, take a list of [Device, Tablets,
// Laptop], created in the class App, and calculate the total amount of the values
// of each class. It's suppose to work with n values of devices.
static float total_devices, total_laptops, total_tablets;
static Device[] devices;
TotalPrice(Device[] a_devices) {
total_devices = 0;
total_laptops = 0;
total_tablets = 0;
devices = a_devices;
}
public void print_totals() {
// This method iterate over the list of devices and add the total price of each
// one to the correspondent variable, the one that gonna be printed
for (int count = 0; count < devices.length; count) {
String name = devices[count].getClass().getSimpleName();
switch (name) {
case "Device": total_devices = devices[count].calc_price(); break;
case "Laptop": total_laptops = devices[count].calc_price(); break;
case "Tablet": total_tablets = devices[count].calc_price(); break;
}
}
System.out.println( "Total price of Devices: " total_devices "\n"
"Total price of Laptops: " total_laptops "\n"
"Total price of Tablets: " total_tablets);
}
}
我在 StackOverflow 中搜索了這里并閱讀了有關多型性和繼承的各種內容，但沒有找到任何具體的解決方案，并且我發現的遠程內容不起作用。我認為錯誤是因為我在java中宣告事物或一些記憶體管理事物的方式，我還不知道，我是新手。
挑戰表明需要使用該結構和所有這些類，我沒有選擇它。我的罪是里面的代碼，而不是定義的變數或類，甚至是App它的類是如何撰寫的，每一個都在類圖中表示，并解釋了挑戰，我想做，因為我從來沒有作業過在 OOP 中使用 UML 圖，并想嘗試編碼一個。
額外的
這是我制作的“測驗不是真正的測驗”，以查看問題是否出在類本身或類似的東西上，并發現這些類單獨作業，當每個類都在自己的變數上宣告時，沒有其他方法中的相關類。
這是一個外部類，我在其中召集每個類并嘗試查看解決問題的另一種方法。
public class Test {
public static void main(String[] args) {
float device_cost = test_device(),
tablet_cost = test_tablet(),
laptop_cost = test_laptop();
System.out.println( "Device: " device_cost "\n"
"Tablet: " tablet_cost "\n"
"Laptop: " laptop_cost "\n");
without_father();
all_at_once();
// Outputs are:
// Device: 700.0
// Tablet: 110.0
// Laptop: 580.0
// Tablet without father: 580.0
// Laptop without father: 580.0
// Device in group: 580.0
// Tablet in group: 580.0
// Laptop in group: 580.0
}
static float test_device() {
Device test_device = new Device((byte) 3, 600, 'D');
return test_device.calc_price();
}
static float test_tablet() {
Tablet test_tablet = new Tablet();
return test_tablet.calc_price();
}
static float test_laptop() {
Laptop test_laptop = new Laptop((byte) 3, 500,'E', 250);
return test_laptop.calc_price();
}
static void without_father() {
Tablet test_tablet = new Tablet();
Laptop test_laptop = new Laptop((byte) 3, 500,'E', 250);
System.out.println( "Tablet without father: " test_tablet.calc_price() "\n"
"Laptop without father: " test_laptop.calc_price() "\n");
}
static void all_at_once() {
Device test_device = new Device((byte) 3, 600, 'D');
Tablet test_tablet = new Tablet();
Laptop test_laptop = new Laptop((byte) 3, 500,'E', 250);
System.out.println( "Device in group: " test_device.calc_price() "\n"
"Tablet in group: " test_tablet.calc_price() "\n"
"Laptop in group: " test_laptop.calc_price() "\n");
}
}
uj5u.com熱心網友回復：
更新
感謝@ScaryWombat 用戶在問題的評論中解決了這個問題。所以問題在于我如何宣告兩件事：
這些變數在宣告為static時被所有類使用。因此，我在Device 類中宣告為受保護，在所有其他類中宣告為私有。
方法calc_consume_w也有同樣的問題，因為我宣告為static，所以我將其更改為public。
這兩個更改解決了問題，App 類保持不變。
新代碼：
類設備
public class Device { protected float price, basis_price = 100f; protected byte weight, basis_weight = 1; protected char consumption_w, basis_consumption_w = 'F'; // ... public float calc_consume_w() { HashMap<Character,Float> cost_w = new HashMap<Character,Float>(); cost_w.put('A', 100f); cost_w.put('B', 80f); cost_w.put('C', 60f); cost_w.put('D', 50f); cost_w.put('E', 30f); cost_w.put('F', 10f); return cost_w.get(Character.toUpperCase(consumption_w)); } // ... }類平板電腦：
public class Tablet extends Device { private float ram, basis_ram = 1; // ... }類筆記本電腦：
public class Laptop extends Device { private float hd, basis_hd = 250; // ... }總價格類：
public class TotalPrice { private float total_devices, total_laptops, total_tablets; private Device[] devices; // ... }
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