Java基础——Collections.sort的两种用法排序详解

    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));  
            }  
        }  
    }  

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);  
        }  
    }  
}