统计字符串中字符个数，通过HashMap和TreeMap分别按value和key排序

package test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;

/**
* 统计字符串中个字符的个数，并通过hashmap按value和key分别排序
* @author USER
*
*/

public class Test1 {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String string = in.nextLine();
findsub(string);
}

private static void findsub(String string) {
// TODO Auto-generated method stub
HashMap<String, Integer> map = new LinkedHashMap<String, Integer>();
char[] ch = string.toCharArray();
for (int i = 0; i < ch.length; i++) {
Integer count = map.get(ch[i]+"");
if (count == null) {
count = 1;
}else {
count = count +1;
}
map.put(ch[i]+"", count);
}

for (String str : map.keySet()) {
System.out.println(str+":"+map.get(str));
}
System.out.println();

//按value排序,通过修改Collections.sort()方法来实现
List<Map.Entry<String, Integer>> list = new ArrayList<Map.Entry<String, Integer>>();
list.addAll(map.entrySet());

Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
@Override
public int compare(Entry<String, Integer> o1,
Entry<String, Integer> o2) {
// TODO Auto-generated method stub
return o2.getValue() - o1.getValue();
//return o1.getKey().toString().compareTo(o2.getKey().toString());
}
});

for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i).getKey()+":"+list.get(i).getValue());
}
System.out.println();

//按key值排序
//方法 一：通过修改Collections.sort()方法来实现
Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {

@Override
public int compare(Entry<String, Integer> o1,
Entry<String, Integer> o2) {
// TODO Auto-generated method stub
return o1.getKey().toString().compareTo(o2.getKey().toString());//升序
//return o2.getKey().toString().compareTo(o1.getKey().toString());//降序
}
});
for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i).getKey()+":"+list.get(i).getValue());
}
System.out.println();

//方法二：通过key转换为数组
Object[] obj = map.keySet().toArray();
Arrays.sort(obj);
for (Object object : obj) {
System.out.println(object+":"+map.get(object));
}
}
}

package test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.TreeMap;
import java.util.Map.Entry;
/**
* 统计字符串中个字符的个数，并通过Treemap按value排序
* 由于TreeMap默认就是按照key的升序排列
* @author USER
*
*/
public class Test2 {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
String string = in.nextLine();
findsub(string);
}

private static void findsub(String string) {
// TODO Auto-generated method stub
TreeMap<String, Integer> map = new TreeMap<String, Integer>();
char[] ch = string.toCharArray();
for (int i = 0; i < ch.length; i++) {
Integer count = map.get(ch[i]+"");
if (count == null) {
count = 1;
}else {
count = count +1;
}
map.put(ch[i]+"", count);
}

for (String str : map.keySet()) {
System.out.println(str+":"+map.get(str));
}
System.out.println();

//按value排序
List<Map.Entry<String, Integer>> list = new ArrayList<Map.Entry<String, Integer>>();
list.addAll(map.entrySet());

Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
@Override
public int compare(Entry<String, Integer> o1,
Entry<String, Integer> o2) {
// TODO Auto-generated method stub
return o2.getValue() - o1.getValue();
//return o1.getKey().toString().compareTo(o2.getKey().toString());
}
});

for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i).getKey()+":"+list.get(i).getValue());
}
}
}