java中Collections.sort排序详解

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);
 }
 }
}