详解Java中Collections.sort排序

package com.tjcyjd.comparator; import java.text.DecimalFormat; import java.text.SimpleDateFormat; import java.util.GregorianCalendar; import java.util.Iterator; import java.util.TreeMap;  public class Book implements Comparable { // 定义名为Book的类，默认继承自Object类   public int id;// 编号   public String name;// 名称   public double price; // 价格   private String author;// 作者   public GregorianCalendar calendar;// 出版日期   public Book() {     this(0, "X", 0.0, new GregorianCalendar(), "");   }   public Book(int id, String name, double price, GregorianCalendar calender,       String author) {     this.id = id;     this.name = name;     this.price = price;     this.calendar = calender;     this.author = author;   }   // 重写继承自父类Object的方法，满足Book类信息描述的要求   public String toString() {     String showStr = id + "\t" + name; // 定义显示类信息的字符串     DecimalFormat formatPrice = new DecimalFormat("0.00");// 格式化价格到小数点后两位     showStr += "\t" + formatPrice.format(price);// 格式化价格     showStr += "\t" + author;     SimpleDateFormat formatDate = new SimpleDateFormat("yyyy年MM月dd日");     showStr += "\t" + formatDate.format(calendar.getTime()); // 格式化时间     return showStr; // 返回类信息字符串   }   public int compareTo(Object obj) {// Comparable接口中的方法     Book b = (Book) obj;     return this.id - b.id; // 按书的id比较大小，用于默认排序   }   public static void main(String[] args) {     Book b1 = new Book(10000, "红楼梦", 150.86, new GregorianCalendar(2009,         01, 25), "曹雪芹、高鄂");     Book b2 = new Book(10001, "三国演义", 99.68, new GregorianCalendar(2008, 7,         8), "罗贯中 ");     Book b3 = new Book(10002, "水浒传", 100.8, new GregorianCalendar(2009, 6,         28), "施耐庵 ");     Book b4 = new Book(10003, "西游记", 120.8, new GregorianCalendar(2011, 6,         8), "吴承恩");     Book b5 = new Book(10004, "天龙八部", 10.4, new GregorianCalendar(2011, 9,         23), "搜狐");     TreeMap tm = new TreeMap();     tm.put(b1, new Integer(255));     tm.put(b2, new Integer(122));     tm.put(b3, new Integer(688));     tm.put(b4, new Integer(453));     tm.put(b5, new Integer(40));     Iterator it = tm.keySet().iterator();     Object key = null, value = null;     Book bb = null;     while (it.hasNext()) {       key = it.next();       bb = (Book) key;       value = tm.get(key);       System.out.println(bb.toString() + "\t库存：" + tm.get(key));     }   } }