java中Collections.sort排序方法简介说明

Collections.sort方法的功能

Collections.sort方法的功能:
     用于对一个sort进行排序操作

Collections.sort方法的语法:
     Collections.sort(list, new UserComparator());

参数说明:
     list:待比较的对象
	 new UserComparator():实现Comparator接口的实现类

User实体类

package com.java265.comparator;
 
import java.text.DecimalFormat;
import java.text.SimpleDateFormat;
import java.util.GregorianCalendar;
import java.util.Iterator;
import java.util.TreeMap;
 
/**
 * 实体类 
 * 
 */
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.java265.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);
		}
	}
}