Java Code to Count Numbers of Characters From String

public class CountNumberOfCharacters {

public static void main(String[] args) {
String s1="abcb";
Map<Character, Integer> map=new HashMap<>();
for(int i=0;i<s1.length();i++){
char ch=s1.charAt(i);
if(map.containsKey(ch)){
map.put(ch, map.get(ch)+1);
}
else{
map.put(ch, 1);
}
}
Set<Character> set=map.keySet();
for(Character c:set){
System.out.println("CHARACTER = "+c+" , OCCURENCE = "+map.get(c));
}
}

}