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，默许继承自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类信息描写的要求 public String toString() { String showStr = id + " " + 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 += " " + formatPrice.format(price);// 格式化价格 showStr += " " + author; SimpleDateFormat formatDate = new SimpleDateFormat("yyyy年MM月dd日"); showStr += " " + 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，用于默许排序 } 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,"3国演义",99.68,new GregorianCalendar(2008,7,8),"罗贯中 "); Book b3 = new Book(10002,"水浒传",100.8,6,28),"施耐庵 "); Book b4 = new Book(10003,"西游记",120.8,new GregorianCalendar(2011,"吴承恩"); Book b5 = new Book(10004,"天龙8部",10.4,9,23),"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() + " 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,"搜狐"); list.add(b1); list.add(b2); list.add(b3); list.add(b4); list.add(b5); // Collections.sort(list); //没有默许比较器，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(" " + 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; // 强迫转换 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; // 强迫转换 Book p2 = (Book) object2; return p2.calendar.compareTo(p1.calendar); } } }