子类给我“符号找不到”的抽象类错误

Question

所以我拿了一些我的compsci教授的例子类，并试图编译他们了解更多关于它，但我得到一个“符号没有找到”的错误。所有的文件都在同一个文件夹里。谁能告诉我怎么解决这件事或者是怎么回事？

下面是抽象类：

    package abstractclass;

/**
   The Element class is introduced to illustrate the use of
    abstract classes.  In this revised version of the PersonSet
    class example, the Person class will inherit from this
    abstract class.  The purpose of the abstract class Element
    is to introduce the "common class protocol" for all of its
    subclasses.  That common class protocol is introduced using
    abstract as well as fully implemented methods.  The abstract
    methods are:
                  readIn
                  display
                  equals
                  clone
    In addition, the abstract class Element fully implements the
    getClassName method.
*/

    public abstract class Element
   {

   // Access method

   /**
      The getClassName method returns the name of the calling object's
    class.
    @return the name of the calling object's class
   */

       public String getClassName()
      {
         // Local data ...
         String resultStr;
                       // Result of applying toString method to
                          // the calling object
         int whereAt;  // Where the @ symbol is in resultStr

         // Logic ...
         resultStr = this.toString();
         whereAt = resultStr.indexOf('@');
         resultStr = resultStr.substring(0,whereAt);
         whereAt = resultStr.indexOf('.');
         return resultStr.substring(whereAt + 1);
      }

      // Abstract methods readIn, display, equals and clone.
      // A direct subclass must implement these abstract methods
    // unless the direct subclass is itself declared "abstract"

       public abstract void readIn();

       public abstract void display();

       public abstract boolean equals(Element dobj);

       public abstract Element clone();
   }

下面是子类Person：

        package abstractclass;

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

    public class Person extends Element
   {
      private String name;        
      private String eMail;       

       public Person()
      {
         name = "";
         eMail = "";
      }

       public Person (String aName)
      {
         name = new String(aName.toUpperCase());
      }

       public Person (Person originalPerson)
      {
         name = new String(originalPerson.name);
         eMail = new String(originalPerson.eMail);
      }

       public String getName()
      {
         return new String(name);
      }

       public String getEMail()
      {
         return new String(eMail);
      }

       public void setName(String aName)
      {
         name = new String(aName.toUpperCase());
      }

       public void setEMail(String anEMail)
      {
         eMail = new String(anEMail);
      }

       public void readIn()
      {
         Scanner keyboard = new Scanner(System.in);
         System.out.print("Name:   ");
         name = keyboard.nextLine().toUpperCase();
         System.out.print("E-Mail: ");
         eMail = keyboard.nextLine();
      }

       public void display()
      {
         System.out.println("Name:   " + name);
         System.out.println("E-mail: " + eMail);
      }

       public boolean equals(Element otherPerson)
      {
         return name.equals(((Person) otherPerson).name);
      }

       public Element clone()
      {
         Person theClone = new Person();
         theClone.name = new String(name);
         theClone.eMail = new String(eMail);
         return theClone;
      }

下面是当我尝试编译person类时它给我的错误：

    Person.java:13: error: cannot find symbol
    public class Person extends Element
                                ^
  symbol: class Element
Person.java:147: error: cannot find symbol
       public boolean equals(Element otherPerson)
                             ^
  symbol:   class Element
  location: class Person
Person.java:158: error: cannot find symbol
       public Element clone()
              ^
  symbol:   class Element
  location: class Person
3 errors

Answer 1

确保这两个类都按照编译器的预期在一个名为abstractClass的文件夹中。编译器在定位从属类时期望文件夹名与包名匹配。