如何使用Java中的用户输入填充构造函数？

Question

我已经在任务中遇到了障碍,并且已经在网站上寻找任何有用的东西(空洞的).我需要创建一个类,该类中的构造函数,然后是一个子类来扩展超类.然后,我需要使用main方法创建一个新文件来演示这两种情况.没问题,从概念上讲.

我的问题是:如何使用构造函数初始化对象,但是使用用户输入？

现在我得到的错误是:"CarRental类中的构造函数CarRental不能应用于给定类型;必需:String,int,String,int found:无参数原因:实际和形式参数列表的长度不同"

请不要嘲笑"错误告诉你问题是什么." 不,它没有告诉我它是什么.我是个小宝贝,需要一点手握.

我将在下面粘贴我的3个课程.他们可能会让你痛苦地翻腾,因为我是一个新手(同样,我的班级是一个缩短的8周课程,几乎没有时间专门用于伪代码,所以我有额外的挑战,构思逻辑本身).

我不是在寻找任何人为我做功课,我只是想在UseCarRental.java文件中寻求帮助.这是我的代码..

public class CarRental {
protected String renterName;
protected int zipCode;
protected String carSize;
protected double dailyRate;
protected int rentalDays;
protected double totalCost;
final double ECONOMY = 29.99;
final double MIDSIZE = 38.99;
final double FULLSIZE = 43.50;

public CarRental(String renterName, int zipCode, String carSize, int rentalDays){

totalCost = dailyRate * rentalDays;
}
public String getRenterName(){
return renterName;
}
public void setRenterName(String renter){
renterName = renter;
}
public int getZipCode(){
return zipCode;
}
public void setZipCode(int zip){
zipCode = zip;
}
public String getCarSize(){
return carSize;
}
public void setCarSize(String size){
carSize = size;
}
public double getDailyRate(){
return dailyRate;
}
public void setDailyRate(double rate){
switch (getCarSize()) {
        case "e":
            rate = ECONOMY;
            break;
        case "m":
            rate = MIDSIZE;
            break;
        case "f":
            rate = FULLSIZE;
            break;
    }
}
public int getRentalDays(){
return rentalDays;
}
public void setRentalDays(int days){
rentalDays = days;
}
public double getTotalCost(){
return totalCost;
}
public void setTotalCost(double cost){
totalCost = cost;
}

public void displayRental(){
System.out.println("==============================================");
System.out.println("Renter Name: " + getRenterName());
System.out.println("Renter Zip Code: " + getZipCode());
System.out.println("Car size: " + getCarSize());
System.out.println("Daily rental cost: $" + getDailyRate());
System.out.println("Number of days: " + getRentalDays());
System.out.println("Total cost: $" + getTotalCost());

}

}

子类LuxuryCarRental ....

public class LuxuryCarRental extends CarRental {

final double chauffeur = 200.00;
final double dailyRate = 79.99;
protected String chauffeurStatus;

public LuxuryCarRental(String renterName, int zipCode, String carSize, int rentalDays) {
    super(renterName, zipCode, carSize, rentalDays);
}

public String getChauffeurStatus(){
return chauffeurStatus;
}
public void setChauffeurStatus(String driver){
chauffeurStatus = driver;
}
public double getChauffeurFee(){
return chauffeur;
}
public void setTotalLuxuryCost(){
if (chauffeurStatus=="y")
    setTotalCost((dailyRate * getRentalDays()) + (chauffeur * getRentalDays()));
else
    setTotalCost(dailyRate * getRentalDays());
}

@Override
public void displayRental(){
System.out.println("==============================================");
System.out.println("Renter Name: " + getRenterName());
System.out.println("Renter Zip Code: " + getZipCode());
System.out.println("Car size: " + getCarSize());
System.out.println("Optional Chauffeur fee: $" + getChauffeurFee());
System.out.println("Daily rental cost: $" + getDailyRate());
System.out.println("Number of days: " + getRentalDays());
System.out.println("Total cost: $" + getTotalCost());

}
}

现在使用main方法的类:

import java.util.Scanner;
public class UseRentalCar {

public static void main(String[] args){
    Scanner keyboard = new Scanner(System.in);
    CarRental rentalCar = new CarRental();

    System.out.println("==========================");
    System.out.println("RENTAL CAR SELECTION");
    System.out.println("==========================");
    System.out.println("Enter your name: ");
    rentalCar.setRenterName(keyboard.next());
    System.out.println("Enter your zip code: ");
    rentalCar.setZipCode(keyboard.nextInt());
    System.out.println("Enter the car size ("e=Economy, m=Midsize, f=Fullsize: ");
    rentalCar.setCarSize(keyboard.next());
    System.out.println("Enter the number of days: ");
    rentalCar.setRentalDays(keyboard.nextInt());

    rentalCar.displayRental();



}
}

(省略一些原因没关系,主要是试图让对象实例化工作)

谢谢你的帮助!!

Answer 1

编译器抱怨CarRental构造函数需要四个参数(String,int,String和另一个int):

"CarRental类中的构造函数CarRental不能应用于给定类型; 必需:String,int,String,int found:无参数原因:实际和形式参数列表的长度不同"

但是在UseRentalCar中,你没有通过任何:

CarRental rentalCar = new CarRental();

"CarRental类中的构造函数CarRental不能应用于给定类型;必需:String,int,String,int found:无参数原因:实际和形式参数列表的长度不同"

如果您没有为您的类提供构造函数,Java将为您创建一个无参数构造函数.如果您提供自己的(在CarRental中使用4个参数),java将不会创建no-arg构造函数,因此您无法引用它.有关详细信息,请参阅http://docs.oracle.com/javase/tutorial/java/javaOO/constructors.html.

您可以自己添加一个无参数构造函数,因为Java没有为您执行此操作.或者既然您为租车类提供了设置器,您可以使用类似于现在的设置器,并在CarRental(和LuxuryCarRental)中删除您的4-arg构造函数,并让Java添加默认值.

或者,如果由于某种原因想要保留这些构造函数,可以将用户输入保存在局部变量中,并将调用推迟到4-arg构造函数,直到完成所有用户输入.

Answer 2

在main方法中创建局部变量,比如String和int变量,然后在用这些变量填充用户输入之后,使用它们来调用构造函数.

我将发布一个通用示例,因为这是作业,最好向您展示概念,然后让您使用该概念来创建代码:

public class Foo {
  private String name;
  private int value;

  public Foo(String name, int value) {
    this.name = name;
    this.value = value;
  }
}

别处

import java.util.Scanner;

public class Bar {

  public static void main(String[] args) {
    Scanner keyboard = new Scanner(System.in);
    System.out.print("Please enter name: ");
    String name = keyboard.nextLine();  // local variable
    System.out.print("Please enter value: " );
    int number = keyboard.nextint();  // another local variable
    keyboard.nextLine();  // to handle the end of line characters

    // use local variables in constructor call
    Foo foo = new Foo(name, number);    
}