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; /**  * 书实体类  *  * @author yjd  *  */ 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));     }   } } 

package com.tjcyjd.comparator; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.GregorianCalendar; import java.util.Iterator; import java.util.List; public class UseComparator {   public static void main(String args[]) {     List<Book> list = new ArrayList<Book>(); // 数组序列     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");     list.add(b1);     list.add(b2);     list.add(b3);     list.add(b4);     list.add(b5);     // Collections.sort(list); //没有默认比较器，不能排序     System.out.println("数组序列中的元素:");     myprint(list);     Collections.sort(list, new PriceComparator()); // 根据价格排序     System.out.println("按书的价格排序:");     myprint(list);     Collections.sort(list, new CalendarComparator()); // 根据时间排序     System.out.println("按书的出版时间排序:");     myprint(list);   }   // 自定义方法：分行打印输出list中的元素   public static void myprint(List<Book> list) {     Iterator it = list.iterator(); // 得到迭代器，用于遍历list中的所有元素     while (it.hasNext()) {// 如果迭代器中有元素，则返回true       System.out.println("/t" + it.next());// 显示该元素     }   }   // 自定义比较器：按书的价格排序   static class PriceComparator implements Comparator {     public int compare(Object object1, Object object2) {// 实现接口中的方法       Book p1 = (Book) object1; // 强制转换       Book p2 = (Book) object2;       return new Double(p1.price).compareTo(new Double(p2.price));     }   }   // 自定义比较器：按书出版时间来排序   static class CalendarComparator implements Comparator {     public int compare(Object object1, Object object2) {// 实现接口中的方法       Book p1 = (Book) object1; // 强制转换       Book p2 = (Book) object2;       return p2.calendar.compareTo(p1.calendar);     }   } }