ArrayList排序

下面是排序的代码：

package com.study;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class ComparableTest {

    public static void main(String[] args) {
        List<Map<String, String>> list = new ArrayList<Map<String, String>>();

        //插入测试数据
        Map<String, String> tmp;
        tmp = new HashMap<String, String>();
        tmp.put("price_section_id", "30");
        tmp.put("name", "liqiu");
        list.add(tmp);
        tmp = new HashMap<String, String>();
        tmp.put("price_section_id", "1");
        tmp.put("name", "baoshan");
        list.add(tmp);
        tmp = new HashMap<String, String>();
        tmp.put("price_section_id", "3");
        tmp.put("name", "yihui");
        list.add(tmp);
        System.out.println(list);

        //比较排序-核心代码
        Comparator<Map<String, String>> comparator = new Comparator<Map<String, String>>() {
            public int compare(Map<String, String> s1, Map<String, String> s2) {
                return new Integer( s1.get("price_section_id").compareTo(s2.get("price_section_id")) );
            }
        };
        Collections.sort(list,comparator);
        System.out.println(list.toString());
    }
}

结果：

[{name=liqiu, price_section_id=30}, {name=baoshan, price_section_id=1}, {name=yihui, price_section_id=3}]
[{name=baoshan, price_section_id=1}, {name=yihui, price_section_id=3}, {name=liqiu, price_section_id=30}]

深入：

1. 查看Collections.sort方法：

    public static <T> void sort(List<T> list, Comparator<? super T> c) {
        Object[] a = list.toArray();
        Arrays.sort(a, (Comparator)c);
        ListIterator i = list.listIterator();
        for (int j=0; j<a.length; j++) {
            i.next();
            i.set(a[j]);
        }
    }

2. Arrays.sort方法

    public static <T> void sort(T[] a, Comparator<? super T> c) {
        if (LegacyMergeSort.userRequested)
            legacyMergeSort(a, c);
        else
            TimSort.sort(a, c);
    }    

3. TimSort 是一个归并排序做了大量优化的版本。对归并排序排在已经反向排好序的输入时表现O(n^2)的特点做了特别优化。对已经正向排好序的输入减少回溯。对两种情况混合（一会升序，一会降序）的输入处理比较好。

链接：http://baike.baidu.com/view/7780831.htm?fr=aladdin