Java基础之集合框架——使用HashMap地图（TryPhoneBook1）

控制台程序。

首先改进Peron类，使Person可以在地图中用作键，进而存储电话簿中的项。必须添加equals()方法并重写默认的hashCode()方法。

 import java.io.*;

 public class Person implements Comparable<Person>, Serializable {
   // Constructor
   public Person(String firstName, String surname) {
     this.firstName = firstName;
     this.surname = surname;
   }

   @Override
   public String toString() {
     return firstName + " " + surname;
   }

   // Compare Person objects
   public int compareTo(Person person) {
     int result = surname.compareTo(person.surname);
     return result == 0 ? firstName.compareTo(person.firstName) : result;
   }

   @Override
   public boolean equals(Object person) {
     return compareTo((Person)person) == 0;
   }

   @Override
   public int hashCode() {
     return 7*firstName.hashCode()+13*surname.hashCode();
   }

   // Read a person from the keyboard
   public static Person readPerson() {
     String firstName = null;
     String surname = null;
     try {
       System.out.print("Enter first name: ");
       firstName = keyboard.readLine().trim();
       System.out.print("Enter surname: ");
       surname = keyboard.readLine().trim();
     } catch(IOException e) {
       System.err.println("Error reading a name.");
       e.printStackTrace(System.err);
       System.exit(1);
     }
     return new Person(firstName,surname);
   }

   private String firstName;                                            // First name of person
   private String surname;                                              // Second name of person
   private static final long serialVersionUID = 1001L;
   private static BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
 }

对于可在散列表中用作键的自定义类对象来说，必须重写Object类的equals()方法。该方法有HashMap<>类中的方法用于确定两个键何时相等。

还可以重写默认的hashCode()方法，将对象的散列值返回为int类型。这个hashCode()方法用于生成一个值，从而确定键/值位于什么地方。

 import java.io.*;

 class PhoneNumber implements Serializable {
   public PhoneNumber(String areacode, String number) {
     this.areacode = areacode;
     this.number = number;
 }

   @Override
   public String toString() {
     return areacode + " " + number;
   }

   // Read a phone number from the keyboard
   public static PhoneNumber readNumber() {
     String area = null;                                                // Stores the area code
     String localcode = null;                                           // Stores the local code
     try {
       System.out.print("Enter area code: ");
       area = keyboard.readLine().trim();
       System.out.print("Enter local code: ");
       localcode = keyboard.readLine().trim();
       System.out.print("Enter the number: ");
       localcode += " " + keyboard.readLine().trim();
     } catch(IOException e) {
       System.err.println("Error reading a phone number.");
       e.printStackTrace();
       System.exit(1);
     }
     return new PhoneNumber(area,localcode);
   }

   private String areacode;
   private String number;
   private static final long serialVersionUID = 1001L;
   private static BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
 }

 import java.io.Serializable;

 class BookEntry implements Serializable {
   public BookEntry(Person person, PhoneNumber number) {
    this.person = person;
    this.number = number;
   }

   public Person getPerson() {
     return person;
   }

   public PhoneNumber getNumber() {
     return number;
   }

   @Override
   public String toString() {
     return person.toString() + '\n' + number.toString();
   }

   // Read an entry from the keyboard
   public static BookEntry readEntry() {
     return new BookEntry(Person.readPerson(), PhoneNumber.readNumber());
   }

   private Person person;
   private PhoneNumber number;
   private static final long serialVersionUID = 1001L;
 }

 import java.io.Serializable;
 import java.util.HashMap;

 class PhoneBook implements Serializable {
   public void addEntry(BookEntry entry) {
     phonebook.put(entry.getPerson(), entry);
   }

   public BookEntry getEntry(Person key) {
     return phonebook.get(key);
   }

   public PhoneNumber getNumber(Person key) {
     BookEntry entry = getEntry(key);
     if(entry != null) {
     return entry.getNumber();
     } else {
       return null;
     }
   }

   private HashMap<Person,BookEntry> phonebook = new HashMap<>();
   private static final long serialVersionUID = 1001L;
 }

 import java.io.StreamTokenizer;
 import java.io.BufferedReader;
 import java.io.InputStreamReader;
 import java.io.IOException;

 public class FormattedInput {

   public int readInt() throws InvalidUserInputException {
     if (readToken() != StreamTokenizer.TT_NUMBER) {
       throw new InvalidUserInputException("readInt() failed." + "Input data not numeric");
     }

     if (tokenizer.nval > (double) Integer.MAX_VALUE || tokenizer.nval < (double) Integer.MIN_VALUE) {
       throw new InvalidUserInputException("readInt() failed." + "Input outside range of type int");
     }

     if (tokenizer.nval != (double) (int) tokenizer.nval) {
       throw new InvalidUserInputException("readInt() failed." + "Input not an integer");
     }
     return (int) tokenizer.nval;
   }

   public double readDouble() throws InvalidUserInputException {
     if (readToken() != StreamTokenizer.TT_NUMBER) {
       throw new InvalidUserInputException("readDouble() failed." + "Input data not numeric");
     }
     return tokenizer.nval;
   }

   public String readString() throws InvalidUserInputException {
     if (readToken() == StreamTokenizer.TT_WORD || ttype == '\"' || ttype == '\"') {
       return tokenizer.sval;
     } else {
       throw new InvalidUserInputException("readString() failed." + "Input data is not a string");
     }
   }
   // Plus methods to read various other data types...

   // Helper method to read the next token
   private int readToken() {
     try {
       ttype = tokenizer.nextToken();
       return ttype;

     } catch (IOException e) {                                          // Error reading in nextToken()
       e.printStackTrace();
       System.exit(1);                                                  // End the program
     }
     return 0;
   }

   // Object to tokenize input from the standard input stream
   private StreamTokenizer tokenizer = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
   private int ttype;                                                   // Stores the token type code
 }

 public class InvalidUserInputException extends Exception {
   public InvalidUserInputException() {  }

   public InvalidUserInputException(String message) {
     super(message);
   }

   private static final long serialVersionUID = 9876L;

 }

 public class TryPhoneBook {
   public static void main(String[] args) {
     PhoneBook book = new PhoneBook();                                  // The phone book
     FormattedInput in = new FormattedInput();                          // Keyboard input
     Person someone;
     while(true) {
       System.out.println("Enter 1 to enter a new phone book entry\n"+
                          "Enter 2 to find the number for a name\n"+
                          "Enter 9 to quit.");
       int what = 0;                                                    // Stores input selection
       try {
         what = in.readInt();

       } catch(InvalidUserInputException e) {
         System.out.println(e.getMessage()+"\nTry again.");
         continue;
       }

       switch(what) {
         case 1:
           book.addEntry(BookEntry.readEntry());
           break;
         case 2:
           someone = Person.readPerson();
           BookEntry entry = book.getEntry(someone);
           if(entry == null) {
             System.out.println("The number for " + someone + " was not found.");
           } else {
             System.out.println("The number for " + someone + " is " + entry.getNumber());
           }
           break;
         case 9:
           System.out.println("Ending program.");
           return;
         default:
           System.out.println("Invalid selection, try again.");
           break;
       }
     }
   }
 }