java求解字符串中出现的最多重复字符及个数

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.Scanner;
import java.util.TreeSet;

/**
* 一个字符串可能包含a~z中的多个字符，允许重复，随机输入一串字符串，
* 求出现次数最多的那个字母及次数
* @author USER
*
*/
public class CheckRepeatString {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.print("输入一串字符串：");
String string = in.nextLine();
CheckRepeatString crs = new CheckRepeatString();
crs.doString(string);
}

public void doString(String input) {
//字符串转化为字符数组，通过ArrayList容器来重新排序，TreeSet容器来剔除重复的元素
char[] ch = input.toCharArray();
ArrayList<String> list = new ArrayList<String>();
TreeSet<String> set = new TreeSet<String>();
for (int i = 0; i < ch.length; i++) {
list.add(String.valueOf(ch[i]));
set.add(String.valueOf(ch[i]));
}
System.out.println(set);
System.out.println(list);
Collections.sort(list);//调用Collections类的sort方法实现对list的排序
System.out.println(list);

//将ArrayList排序好的数组转化为字符串
StringBuffer sb = new StringBuffer();
for (int i = 0; i < list.size(); i++) {
sb.append(list.get(i));
}
input = sb.toString();
System.out.println(input);

//通过TreeSet中无重复字符来求取对应重复字符的个数
int max = 0;
String maxString = "";
ArrayList<String> repeatList = new ArrayList<String>();//保存重复字符
Iterator<String> iterator = set.iterator();//对set容器遍历
while (iterator.hasNext()) {
String str = iterator.next();
int begin = input.indexOf(str);
int end = input.lastIndexOf(str);
int value = end - begin +1;
if (value > max) {
max = value;
maxString = str;
repeatList.add(str);
}else if (value == max) {
repeatList.add(str);
}
}

//输出最大重复的字符串字符和个数
System.out.print("最多字符为：");
for (int i = 0; i < repeatList.size(); i++) {
if (repeatList.get(i).equals(maxString)) {
System.out.print(repeatList.get(i)+" ");
}
}
System.out.println();
System.out.println("最多的个数为："+max);

}
}