일단 짠 클래스 3개의 소스를 올려 보면,

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PDApplication.class

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public class PDApplication {
 public static void main(String args[]) {
  if (args.length == 0) {
   System.err.println("You must provide the name of the file"
     + " that contains the phone directory.");
   System.exit(1);
  }
  PhoneDirectory phoneDirectory = new ArrayBasedPD();
  phoneDirectory.loadData(args[0]);
  
  PDUserInterface phoneDirectoryInterface = new PDGUI();
  phoneDirectoryInterface.processCommands(phoneDirectory);
 }

}

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PhoneDirectory.class

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public class ArrayBasedPD implements PhoneDirectory
{
 private static final int INITIAL_CAPACITY = 100;
 private int capacity = INITIAL_CAPACITY;
 private int size = 0;
 
 private DirectoryEntry[] theDirectory =
  new DirectoryEntry[capacity];
 
 private String soureName = null;
 private boolean modified = false;
 
 public void loadData(String sourceName) {
  this.sourceName = sourceName;
  try {
   BufferedReader in = new BufferedReader(new FileReader(sourceName));
   String name;
   String numer;
   while ((name = in.readLine()) != null) {
    if ((number = in.readLine()) == null) {
     break;
    }
    add(name, number);
   }
   in.close();
  }
  catch (FileNotFoundException ex) {
   return;
  }
 }
 public String addOrChangeEntry(String name, String number) {
  String oldNumber = null;
  int index = find(name);
  if (index > -1) {
   oldNumber = theDirectory[index].getNumber();
   theDirectory[index].setNumber(number);
  }
  else {
   add(name, number);
  }
  modified = true;
  return oldNumber;
 }
 public String lookupEntry(String name) {
  int index = find(name);
  if (index > -1) {
   return theDirectory[index].getNumber();
  }
  else {
   return null;
   
  }
 }
 public void save() {
  if (modified) {
   try {
    PrintWriter out = new PrintWriter(new FileWriter(sourceName));
    for (int i = 0; i < size; i++) {
     out.println(theDirectory[i].getName());
     out.println(theDirectory[i].getNumber());   
    }
    out.close();
    modified = false;
   }
   catch (Exception ex) {
    System.err.println("Save of directory failed");
    ex.printStackTrace();
    System.exit(1);
   }
  }
 }
 private int find(String name) {
  for (int i = 0; i < size; i++) {
   if (theDirectory[i].getName().equals(name)) {
    return i;
   }
  }
  return -1;
 }
 
 private void add(String name, String number) {
  if (size >= capacity) {
   reallocate();
  }
  theDirectory[size] = new DirectoryEntry(name, number);
  size++;
 }
 private void reallocate() {
  capacity *= 2;
  DirectoryEntry[] newDirectory = new DirectoryEntry[capacity];
  System.arraycopy(theDirectory, 0, newDirectory, 0,
    theDirectory.length);
  theDirectory = newDirectory;
 }
 
 public String removeEntry(String name) {
 }
}

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PDGUI.class

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public class PDGUI implements PDUserInterface {
 private PhoneDirectory theDirectory = null;
 
 public void processCommands(PhoneDirectory thePhoneDirectory) {
  
  String[] commands = {
    "Add/Change Entry",
    "Look Up Entry",
    "Remove Entry",
    "Save Directory",
    "Exit"};
  
  theDirectory = thePhoneDirectory;
  int choice;
  do {
   choice = JOptionPane.showOptionDialog(null, "Select a Command",
     "PhoneDirectory",
     JOptionPane.YES_NO_CANCEL_OPTION,
     JOptionPane.QUESTION_MESSAGE, null,
     commands, commands[commands.length - 1]);
   switch (choice) {
   case 0: doAddChangeEntry(); break;
   case 1: doLookupEntry();    break;
   case 2: doRemoveEntry();    break;
   case 3: doSave();           break;
   case 4: doSave();           break;
   }
  }
  while (choice < commands.length - 1);
  System.exit(0);
 }
 private void doAddChangeEntry() {
  String newName = JOptionPane.showInputDialog("Enter name");
  if (newName == null) {
   return;
  }
  String oldNumber = theDirectory.addOrChangeEntry(newName, newNumber);
  String message = null;
  if (oldNumber == null) {
   message = newName + " was added to the directory"
   + "\\nNew number: " + newNumber;
  }
  else {
   message = "Number for " + newName + " was changed "
   + "\\nOld number: " + oldNumber
   + "\\nNew number: " + newNumber;
  }
  JOptionPane.showMessageDialog(null, message);
 }
 private void doLookupEntry() {
  String theName = JOptionPane.showInputDialog("Enter name");
  if (theName == null) {
   return;
  }
  String theNumber = theDirectory.lookupEntry(theName);
  String message = null;
  if (theNumber != null) {
   message = "The number for " + theName + " is " + theNumber;
  }
  else {
   message = theName + " is not listed in the directory";
  }
  JOptionPane.showMessageDialog(null, message);
 }
 private void doRemoveEntry() {
 }
 private void doSave() {
  theDirectory.save();
 }
}

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이렇게 3클래스입니다. 소스코드를 보면 여기저기서

~~~ cannot be solved to a type 이라는 에러 문구가 뜨네요. 어떻게 해야 좋을까요?

도움 좀 부탁드립니다. 해결 할 방법 없나요? 제가 짠 소스는 아니고 그냥 책 같은데에

나와있는데로 그대로 한건데 에러가 나네요 ㅠㅠ 도와주세요