选取字符创中最长字符，并统计出现次数

package test;

import java.util.HashMap;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		@SuppressWarnings("resource")
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		long timestart=System.currentTimeMillis();
		HashMap
 
  map=map(str);
		if(map.values().isEmpty()){
			System.out.println("null");
			return;
		}
		for(String key:map.keySet()){
			System.out.println(key+":"+map.get(key));
		}
		long timeend=System.currentTimeMillis();
		System.out.println((timeend-timestart));
		
	}
	public static HashMap
  
   map(String str){ HashMap
   
     map=new HashMap
    
     (); for(int i=str.length()-1;i>0;i--){ String[]strs=new String[str.length()-i+1]; for(int j=0;j