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() + '
' + 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
"+
                         "Enter 2 to find the number for a name
"+
                         "Enter 9 to quit.");
      int what = 0;                                                    // Stores input selection
      try {
        what = in.readInt();

      } catch(InvalidUserInputException e) {
        System.out.println(e.getMessage()+"
Try 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;
      }
    }
  }
}