Question

每当我运行程序时，都不会显示任何内容。在控制台窗口中，所有可见的都是空白空格。

截图： enter image description here

以下是我的代码粘贴：

import java.util.Scanner;

public class Foothill
{
   public static void main(String[] args)
   {
      // declare the references
      //warning for line below
      HeartRates heartrates;
      //warning for line above: the value of the local variable heartrates is not used

      // instantiate the object
      heartrates = new HeartRates();
   }
}

class HeartRates {

   // member data
   public String firstName, lastName;
   public int birthMonth, birthDay, birthYear, personAge, maxRate, minRange, maxRange;

   // default constructor
   HeartRates() {
   }

   // 2-parameter constructor
   HeartRates (String userFirstname, String userLastname, int userBirthmonth, int userBirthday, int userBirthYear, int userAge, int heartMax, int userMin, int userMax){
      firstName = userFirstname;
      lastName = userLastname;
      birthMonth = userBirthmonth;
      birthDay = userBirthday;
      birthYear = userBirthYear;
      personAge = userAge;
      maxRate = heartMax;
      minRange = userMin;
      maxRange = userMax;
   }

   // accessor "get" methods --------------------------------
   public String getFirstname(String userFirstname, String firstName) {
      firstName = userFirstname;
      Scanner inputStream = new Scanner (System.in);
      userFirstname = inputStream.nextLine();
      System.out.print("Your first name is: " + userFirstname);
      inputStream.close();
      return firstName;
   }
   public String getLastName(String userLastname, String lastName){
      lastName = userLastname;
      Scanner inputStream = new Scanner (System.in);
      userLastname = inputStream.nextLine();
      System.out.print("Your last name is: " +userLastname);
      inputStream.close();
      return lastName;
   }
   public int getBirthmonth(int userBirthmonth, int birthMonth){
      birthMonth = userBirthmonth;
      Scanner inputStream = new Scanner (System.in);
      userBirthmonth = inputStream.nextInt();
      int monthBirth = Integer.parseInt("userBirthmonth");
      System.out.print(monthBirth);
      inputStream.close();
      return birthMonth;
   }
   public int getBirthday(int userBirthday, int birthDay){
      birthDay = userBirthday;
      Scanner inputStream = new Scanner (System.in);
      userBirthday = inputStream.nextInt();
      int dayBirth = Integer.parseInt("userBirthday");
      System.out.print(dayBirth);
      inputStream.close();
      return birthDay;
   }
   public int getBirthyear(int userBirthyear, int birthYear){
      birthYear = userBirthyear;
      Scanner inputStream = new Scanner (System.in);
      userBirthyear = inputStream.nextInt();
      int yearBirth = Integer.parseInt("userBirthyear");
      System.out.print(yearBirth);
      inputStream.close();
      return birthYear;
   }
   public int getAge(int birthMonth, int birthDay, int birthYear, int userAge){
      personAge = userAge;
      Scanner inputStream = new Scanner (System.in);
      System.out.print("Please enter the current month in numbers: ");
      int theMonth = inputStream.nextInt();
      System.out.print("Please enter the current day in numbers: ");
      int theDay = inputStream.nextInt();
      System.out.print("Please enter the current year in numbers: ");
      int theYear = inputStream.nextInt();
      userAge = theYear - birthYear;
         if ((theMonth == birthMonth && theDay < birthDay) || theMonth < birthMonth){
            userAge--;
            System.out.println("Your date of birth is: " + birthMonth + "/" + birthDay + "/" + birthYear);
            System.out.println("You are " + userAge + " years old.");
         }
         else {
            System.out.println("Your are " + userAge + " years old.");
         }
      inputStream.close();
      return userAge;
   }
   public int getMaximumHeartRate(int heartMax, int userAge, int maxRate){
      maxRate = heartMax;
      heartMax = 220 - userAge;
      return maxRate;
   }
   public double getMinTargetHeartRate(int heartMax, int userMin, int minRange){
      minRange = userMin;
      userMin = (int)(heartMax*0.5);
      return minRange;
   }
   public int getMaxTargetHeartRate(int heartMax, int userMax, int maxRange){
      maxRange = userMax;
      userMax = (int)(heartMax*0.85);
      return maxRange;
   }
   public void getTargetHeartRange(int heartMax, int userMin, int userMax){
      System.out.println("Your maximum heart rate is " + heartMax + "beats per minute.");
      System.out.print("Your target-heart-rate range is from " + userMin + " to " + userMax + " beats per minute.");
   }

   // accessor "set" method -------------------------------
   public void setFirstname(String userFirstname, String firstName){
      firstName = userFirstname;
   }
   public void setLastname(String userLastname, String lastName){
      lastName = userLastname;
   }
   public void setBirthmonth(int userBirthmonth, int birthMonth){
      birthMonth = userBirthmonth;
   }
   public void setBirthday(int userBirthday, int birthDay){
      birthDay = userBirthday;
   }
   public void setBirthyear(int userBirthyear, int birthYear){
      birthYear = userBirthyear;
   }
   public void setAge(int userAge, int personAge){
      personAge = userAge;
   }
   public void setMaximumHeartRate(int heartMax, int maxRate){
      maxRate = heartMax;
   }
   public void setMinTargetHeartRate(int userMin, int minRange){
      minRange = userMin;
   }
   public void setMaxTargetHeartRate(int userMax, int maxRange){
      maxRange = userMax;
   }

}

我是Java的初学者，从我的代码中你可以说我正在努力掌握创建类，方法和实例化对象的概念。事实上，我们应该打印出来自对象的所有信息，但我不太明白这意味着什么。我所拥有的大部分内容都来自在线或我的书中的例子。我知道有类似的问题，但我认为我的情况略有不同。非常感谢你。

Answer 1

在代码中向控制台输出内容的函数是public int getAge(...)或getTargetHeartRange(..)，它们从不被调用。您只在对象上调用了无参数构造函数，然后没有执行任何其他操作。如果您希望它们起作用，您必须实际调用这些函数。

类似的东西：

heartrates.getTargetHeartRange(fill in your arguments);

在您的情况下，如果您想要打印有意义的内容，我建议您实际为这些成员变量设置一些值（即在实例化对象后使用您的setter函数）。

Answer 2

我认为问题的直接原因是除了创建HeartRate实例之外，您的程序似乎没有做任何事情。如果您的代码实际调用了System.out.println(...)调用的方法之一，您将只获得一些输出。

如果你只是想看一些输出，只需改变它：

  heartrates = new HeartRates();

到

  System.out.println("Offering low rates on second hand hearts!");
  heartrates = new HeartRates();

第二个问题是您的代码每次要阅读时都会创建一个新的Scanner(System.in)对象。这是一个坏主意，它可能会导致问题。根据您调用的Scanner方法（以及输入流的性质），您最终可能会进行“预读”。如果发生这种情况，则无法再从System.in读取已读取的字符。

您应该做的只是创建一个Scanner(System.in)对象，并将其放入私有字段。

（更好的是从设计的角度来看，重构你的代码，以便HeartRate对象根本不负责读取/解析用户的输入。但是，这可能是你没有做好准备的“教训”还没有。）

Java：控制台不显示任何输出

2 个答案: