Duplicate Char

package interview;
//count no. of duplicate character occurance
import java.util.*;
//steps:
//string --->char array---->(convert to lowercase)---->hashmap
public class DuplicateChar {

public static void main(String[] args)
{
  String str  ="programming world445";
  char[] ch = str.toCharArray();
  char[] upper_ch = convertLower(ch);
  System.out.println(upper_ch);
 
  Map<Character, Integer> map = new HashMap<>();
  for(char c : upper_ch)
  {
  if(map.containsKey(c))
  {
  map.put(c, map.get(c)+1);
  }
  else
  {
  map.put(c, 1);
  }
  }
 
  //****************
  for(Map.Entry<Character,Integer>entry : map.entrySet())
  {
  if(entry.getValue()>1)
  {
  System.out.println(entry.getKey()+"-->"+entry.getValue());
  }
  }
 
 
}
//***********************************
private static char[] convertLower(char[] ch)
{
  for(int i=0;i<ch.length;i++)
  {
  if(Character.isLetter(ch[i])&& (Character.isLowerCase(ch[i])))
    {
  ch[i]= Character.toUpperCase(ch[i]); 
}
  }
return ch;
}


}