import java.util.HashMap; import java.util.Map; public class Main { private Map<Character, Integer> charCountMap; public Main(String s) { initializeCharCountMap(s); } private void initializeCharCountMap(String s) { charCountMap = new HashMap<>(); for (int i = 0; i < s.length(); i++) { char ch = s.charAt(i); if (!charCountMap.containsKey(ch)) { charCountMap.put(ch, 1); } else { charCountMap.put(ch, charCountMap.get(ch) + 1); } } } public int getCountOf(char ch) { if (charCountMap.containsKey(ch)) return charCountMap.get(ch); return 0; } public static void main(String[] args) { Main ob = new Main("Hello from w3cschool.cn"); System.out.println(ob.getCountOf('o')); } }