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;
}
}
}
}