Java - 语法让我很难过

Question

我认为我的代码存在一些基本问题.我不太熟悉java语法,所以我不太确定我哪里出错了.任何帮助将不胜感激.

我试图在中间使用一个构造函数,并在底部使用一些访问器,但我认为我已经为自己过度复杂了.

import java.util.Scanner;    
public class FerryBooking {

    public static void main(String args[]){
        class VehicleBooking {
            private String booking_ID = new String("");
            private String registration = new String("");
            private String make_model = new String("");
            private int number_passengers = 1;
            private boolean insurance_choice = false;
            private boolean insurance_flag = false;

            public static final int booking_fee= 100;
            public static final int extra_passenger = 50;
            public static final int insurance_fee = 50;

            VehicleBooking() {
                Scanner input = new Scanner(System.in);
                Scanner scan = new Scanner(System.in);

                System.out.print("Enter booking ID");
                booking_ID = input.next();
                System.out.print("Enter registration number");
                registration = input.next();
                System.out.print("Enter vehicle make/model");
                make_model = input.next();
                System.out.print("Enter number of passengers");
                number_passengers = scan.nextInt();
            }

            public String getBookingID(){
                return booking_ID;
            }
            public String getRegistration(){
                return registration;
            }
            public String getMakeModel(){
                return make_model;
            }
            public int getPassengers(){
                return number_passengers;
            }
            public boolean getInsurance(){
                return insurance_choice;
            }
            public boolean addInsurance(){
                insurance_choice = true;
                if (insurance_flag = false) {
                    insurance_flag = true;
                    return true;
                } else if (insurance_flag = true) {
                    return false;
                }
                return true;
            }
            public double getBookingFee(){
                int final_cost = booking_fee + (getPassengers()*extra_passenger);
                if (insurance_choice = true){
                    final_cost = final_cost + insurance_fee;
                }
                return final_cost;
            }
        }
    }
}

- 编辑 -

我重写了很多代码,并将其调整到我的重大问题的位置; 构造函数.但是我收到了与构造函数相关的错误以及提供给我的代码.

import java.util.Scanner;

public class VehicleBooking {

    private String booking_ID = "";
    private String registration = "";
    private String make_model = "";
    private int number_passengers = 1;
    private boolean insurance_choice = false;

    public static final int BOOKING_FEE= 100;
    public static final int EXTRA_PASSENGER = 50;
    public static final int INSURANCE_FEE = 50;

    public VehicleBooking(String booking_ID1, String registration1,  String make_model1, int number_passengers1) {

        /** Initialise the variables **/
        booking_ID = booking_ID1;
        registration = registration1; 
        make_model = make_model1;
        number_passengers = number_passengers1;
    }

    public static void main(String args[]) {
        VehicleBooking vb = new VehicleBooking(booking_ID1, registration1, make_model1, number_passengers1);
    }       
}

Answer 1

首先不要像下面那样初始化一个String: -

private String booking_ID = new String("");

而是使用String.valueOf()或只是为变量分配一个空字符串: -

private String booking_ID = "";

第二,养成CONSTANTS用UPPER_CASE信来宣告你的习惯: -

public static final int BOOKING_FEE = 100;

第三,看看你的构造函数: -

    VehicleBooking()  {
        Scanner input = new Scanner(System.in);
        Scanner scan = new Scanner(System.in);

        System.out.print("Enter booking ID");
        booking_ID = input.next();
        System.out.print("Enter registration number");
        registration = input.next();
        System.out.print("Enter vehicle make/model");
        make_model = input.next();
        System.out.print("Enter number of passengers");
        number_passengers = scan.nextInt();
    }

你永远不应该I/O在构造函数中进行操作.. Constructors用于初始化对象的状态.它的唯一目的是initialize.

对于I/O目的,请创建不同的方法readInput(),并在创建对象后调用它.

另一件事: - 这是你if-else-if用过的街区..

         if (insurance_flag = false) {
             insurance_flag = true;
             return true;
         } else if (insurance_flag = true) {
             return false;
         }

在这段代码中,你if永远都是,false而你else if永远都是true......因为你实际上是将这些分配values给你的insurance_flag..你应该==用于比较目的..

所以,使用if (insurance_flag == false)..实际上你不需要与布尔文字进行比较......

只需使用: - if (!insurance_flag)..它们是等价的..

理想情况下,您应该将包含上述内容的方法更改为以下方法: -

       public boolean addInsurance(){
            boolean returnValue = !insurance_flag;
            insurance_flag = true;
            return returnValue;
       }

因为这是你的方法正在做的事情,但是以一种奇怪的方式......

您也可以final_cost = final_cost + insurance_fee;使用以下代码替换: -

final_cost += insurance_fee;

通过这种方式使用它,final_cost将不会被评估twice..

编辑**: -

你constructor应该这样: -

public VehicleBooking(String bookingId, String registration, String makeModel, 
                      String numberOfPassengers)  {

    /** Initialize the instance variables **/
    /** this represent the reference to current object **/
    this.booking_ID = bookingId;
    this.registration = registration; 
    this.make_model = makeModel;
    this.number_passengers = numberOfPassengers;
}

所以,您实际上是将您读取的值传递给构造函数作为参数,并使用这些参数初始化您的实例属性.

我想这会清除你的怀疑..