对HashMap中的实体类进行排序

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package demo20130414;

import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.ArrayList;
import java.util.List;
public class CharCounterDemo {
    /**
     */
    public static void main(String[] args) {
        String str = "aabbccdderffisfalgjgosdrugnsdsduhgdsfugsdogosdjgosdig";
        Map<Character, Integer> map = countAll(str);
        System.out.println(map);
        // 迭代Map： 迭代所有的key，迭代所有的value迭代Entry<key,value>
        // 迭代所有的value，实现统计所有的字符总数
        Collection<Integer> values = map.values();
        Iterator<Integer> ite = values.iterator();
        int total = 0;
        while (ite.hasNext()) {
            Integer n = ite.next();
            total += n;
            System.out.print(n + " ");
        }
        System.out.println("字符总数：" + total);
        // 迭代所有的key，利用迭代所有字符实现输出统计表格
        Set<Character> keys = map.keySet();
        System.out.println("字符串中所有字符的个数：" + keys.size());
        ArrayList<Character> list = new ArrayList<Character>(keys);
        Collections.sort(list);// 自然排序
        for (Iterator<Character> i = list.iterator(); i.hasNext();) {
            Character ch = i.next();
            int n = map.get(ch);
            System.out.print(ch + ":");
            System.out.println(n + " " + ((float) n / total) * 100 + "%");
            // System.out.print(ch);
        }
        System.out.println("照字符出现的数量排序输出:");
        //迭代Entry<key:Value> 实现按照字符出现的数量排序输出
        Set<Entry<Character, Integer>> entries = map.entrySet();
        List<Entry<Character,Integer>> entList=new ArrayList<Entry<Character,Integer>>(entries);
        Collections.sort(entList, new ByValue());
        for (Iterator<Entry<Character, Integer>> i = entList.iterator(); i.hasNext();) {
                Entry<Character,Integer> entry=i.next();
                Character ch=entry.getKey();
                Integer n=entry.getValue();
                System.out.print(ch + ":");
                System.out.println(n + " " + ((float) n / total) * 100 + "%");
        }
    }

    private static Map<Character, Integer> countAll(String str) {
        int length = str.length();
        Map<Character, Integer> map = new HashMap<Character, Integer>();
        for (int i = 0; i < length; i++) {
            char ch = str.charAt(i);
            if (map.containsKey(ch)) {// 如果包含ch
                int n = map.get(ch);
                map.put(ch, n + 1);
            } else {// 如果不包含ch
                map.put(ch, 1);
            }
        }
        return map;
    }
}
class ByValue implements Comparator<Entry<Character,Integer>>{
    public int compare(Entry<Character, Integer> o1,
            Entry<Character, Integer> o2) {
        // TODO Auto-generated method stub
        return -(o1.getValue()-o2.getValue());//从大到小排列
        //return (o1.getValue()-o2.getValue());//从小到大排列
    }
}

转自：http://www.cdtarena.com/javapx/201305/8568.html