Java基础之集合框架——使用集合Vector<>挑选演员（TryVector）

控制台程序。

 1 public class Person implements Comparable<Person> {
 2   // Constructor
 3   public Person(String firstName, String surname) {
 4     this.firstName = firstName;
 5     this.surname = surname;
 6   }
 7 
 8   @Override
 9   public String toString() {
10     return firstName + " " + surname;
11   }
12 
13   // Compare Person objects
14   public int compareTo(Person person) {
15     int result = surname.compareTo(person.surname);
16     return result == 0 ? firstName.compareTo(person.firstName) : result;
17   }
18 
19   private String firstName;            // First name of person
20   private String surname;              // Second name of person
21 }

使用sort()方法对列表排序时，必须通过某种方式确定列表中对象的顺序。最合适的方式就是在Person类中实现Comparable<>接口。Comparable<>只声明了comparableTo()方法。

如果集合中存储的对象的类型实现了Comparable<>接口，就可以把集合对象作为参数传送给sort()方法。

 1 import java.util.Vector;
 2 import java.util.ListIterator;
 3 import java.util.Collections;
 4 import java.io.*;
 5 
 6 public class TryVector {
 7   public static void main(String[] args) {
 8     Person aPerson = null;                                             // A person object
 9     Vector<Person> filmCast = new Vector<>();
10 
11     // Populate the film cast
12     while(true) {                                                      // Indefinite loop
13       aPerson = readPerson();                                          // Read in a film star
14       if(aPerson == null) {                                            // If null obtained...
15         break;                                                         // We are done...
16       }
17       filmCast.add(aPerson);                                           // Otherwise, add to the cast
18     }
19 
20     int count = filmCast.size();
21     System.out.println("You added " + count + (count == 1 ? " person":  " people") + " to the cast:");
22     // Show who is in the cast using an iterator
23     ListIterator<Person> thisLot = filmCast.listIterator();
24 
25     while(thisLot.hasNext()) {       // Output all elements
26       System.out.println( thisLot.next());
27     }
28     System.out.println("
The vector currently has room for " + (filmCast.capacity() - count) + " more people.");
29 
30     // Now sort the vector contents and list it
31     Collections.sort(filmCast);
32     System.out.println("
The cast in ascending sequence is:");
33     for(Person person : filmCast) {
34       System.out.println(person);
35     }
36   }
37 
38   // Read a person from the keyboard
39   static Person readPerson() {
40     // Read in the first name and remove blanks front and back
41     String firstName = null;
42     String surname = null;
43     System.out.println("
Enter first name or ! to end:");
44     try {
45       firstName = keyboard.readLine().trim();                          // Read and trim a string
46 
47       if(firstName.charAt(0) == '!') {                                 // Check for ! entered
48         return null;                                                   // If so, we are done...
49       }
50 
51       // Read in the surname, also trimming blanks
52       System.out.println("Enter surname:");
53       surname = keyboard.readLine().trim();                            // Read and trim a string
54     } catch(IOException e) {
55       System.err.println("Error reading a name.");
56       e.printStackTrace();
57       System.exit(1);
58     }
59     return new Person(firstName,surname);
60   }
61 
62 
63   static BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
64 }

把filmCast对象传送给Collections类的sort()静态方法，就会导致对集合中的对象排序。

键盘对象是InputStreamReader对象中封装的System.in，而InputStreamReader对象封装在BufferedReader对象中。InputStreamReader对象可以把输入从字节流System.in转换为字符。BufferedReader对象缓存了从InputStreamReader读入的数据。因为输入包含一系列字符串，而每个字符串占一行，所以readLine()方法可以完成我们需要的工作。