We would like to know how to count the occurences of each character in a String with Hashmap.
import java.util.Map; import java.util.TreeMap; //from w w w . j a v a 2 s .co m public class Main { public static void main(String[] args) { String str = "this is a test"; char[] char_array = str.toCharArray(); Map<Character, Integer> charCounter = new TreeMap<Character, Integer>(); for (char i : char_array) { charCounter.put(i, charCounter.get(i) == null ? 1 : charCounter.get(i) + 1); } for (Character key : charCounter.keySet()) { System.out.println("occurrence of '" + key + "' is " + charCounter.get(key)); } } }
The code above generates the following result.