Question

好的，所以我应该创建Person类，其中包含用于保存人名，地址和电话号的字段，稍后将由客户类扩展。

    public class Person
{
   //Instance Variables
   private String name;
   private String street;
   private String cityStateZip;
   private String phone;

   //Constructors
   public Person()
   {
      String name = "";
      String street = "";
      String cityStateZip = "";
      String phone = "";
   }
   public Person(String name, String street, String cityStateZip,
                  String phone)
   {
      this.name = name;
      this.street = street;
      this.cityStateZip = cityStateZip;
      this.phone = phone;
   }
   public Person(Person person)
   {
      new Person();
   }

   //Mutators
   public void setName(String name)
   {
      this.name = name;
   }
   public void setStreet(String street)
   {
      this.street = street;
   }
   public void setCityStateZip(String cityStateZip)
   {
      this.cityStateZip = cityStateZip;
   }
   public void setPhone(String phone)
   {
      this.phone = phone;
   }

   //Accessors
   public String getName()
   {

   return name;
   }
   public String getStreet()
   {

   return street;
   }
   public String getCityStateZip()
   {

   return cityStateZip;
   }
   public String getPhone()
   {

   return phone;
   }
   public String toString()
   {

   return name + "/n" + street + "/n" + cityStateZip + "/n" + phone;
   }    
}

好吧，所以...我改变了一些代码，修复了我的私人/公共错误......我永远得到了+/-混合....这个文件现在编译。我试图创建一个类来测试它，并且我遇到了一些问题。这是我目前遇到的错误

---- jGRASP exec：javac -g TestPerson.java

TestPerson.java:23: error: cannot find symbol
      name = keyboard.nextLine;
                     ^
  symbol:   variable nextLine
  location: variable keyboard of type Scanner
TestPerson.java:27: error: cannot find symbol
      street = keyboard.nextLine;
                       ^
  symbol:   variable nextLine
  location: variable keyboard of type Scanner
TestPerson.java:31: error: cannot find symbol
      cityStateZip = keyboard.nextLine;
                             ^
  symbol:   variable nextLine
  location: variable keyboard of type Scanner
TestPerson.java:35: error: cannot find symbol
      phone = keyboard.nextLine;
                      ^
  symbol:   variable nextLine
  location: variable keyboard of type Scanner
TestPerson.java:38: error: non-static method getName() cannot be referenced from a static context
      getName()+ "\n" + getStreet() + "\n" + getCityStateZip() + "\n" 
      ^
TestPerson.java:38: error: non-static method getStreet() cannot be referenced from a static context
      getName()+ "\n" + getStreet() + "\n" + getCityStateZip() + "\n" 
                        ^
TestPerson.java:38: error: non-static method getCityStateZip() cannot be referenced from a static context
      getName()+ "\n" + getStreet() + "\n" + getCityStateZip() + "\n" 
                                             ^
TestPerson.java:39: error: non-static method getPhone() cannot be referenced from a static context
      + getPhone());
        ^
8 errors



 import java.util.Scanner;
import java.io.*;

public class TestPerson extends Person 
{


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

      String name;
      System.out.println("Enter your name: ");
      name = keyboard.nextLine;

      String street;
      System.out.println("Enter your street: ");
      street = keyboard.nextLine;

      String cityStateZip;
      System.out.println("Enter your city, state and zip code: ");
      cityStateZip = keyboard.nextLine;

      String phone;   
      System.out.println("Enter your phone number: ");
      phone = keyboard.nextLine;

      System.out.println("Tested person's information is as follows: " +
      getName()+ "\n" + getStreet() + "\n" + getCityStateZip() + "\n" 
      + getPhone());
      System.out.println(new Person());

      System.exit(0);
   }
}

Answer 1

您获得的确切错误是因为您正在采用以前的公共方法（toString）并将其作为私有方法。

您的Person类的类型为Object，因为Java中的所有类都继承自Object。任何通过Object的人都希望它拥有可以使用的toString方法。如果toString是私有的，则他们无法执行此操作，因此Java会抱怨。

另外，toString中的代码也看起来不对。

Answer 2

private String toString()

您正在覆盖Object's toString方法，其限制条件比public更严格，但不遵守method overriding中java的规则。

应该是

public String toString()

Answer 3

If you want to access your person class and its details in other class 
you   should not make person class constructor as private .if so you 
can't    create a object of person class in other tester classes.  
try it as public.   

Private constructor can be used for **Static factory method()** inside
the class itself and also some utility based classes and also for static 
method(which is for no object creation).

      If you make toString() as private, for this a protected 
instance method in the superclass can be made public,  but not private, 
in the subclass.

This because inheritance creates an IS-A relation between two classes, 
for which the Liskov substitution principle must be valid. Without 
having the previous constraint that would be impossible to enforce.

Answer 4

toString()需要公开，因为其他方法（例如println()）需要访问它。

一般来说，你需要考虑什么应该是私人的，什么应该公开。你已经将一切都变得私密，即使那些没有意义（构造者）。你的吸气剂和制定者也应该是公开的;这是吸气剂和制定者的重点。

尝试测试Person类，但不成功。

4 个答案: