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CS480L MID Q8 String Frequency

Last update: 11/9/2016 10:58:00 AM


The following Java program has been published to figure out how many times each of letters appears in a given string by calculating frequency of them. The program basically uses a TreeMap which is one of the JCF (Java Collection Framework) objects to store characters to avoid counting them more than once. The TreeMap object alphaMap is used to store characters and their frequency values as key value pairs. First, the program checks if each character that is analyzed in string is counted before by looking up in alphaMap. If it finds out that related character have already used before, then it skips and passes on another character to count it. Otherwise, it counts a new character, then it saves it in alphaMap. Finally, helping a Iterator object, all data is printed in console. The method count() returns the actual frequency value of a character in the string.

package com.fatihkabakci.week05;

import java.util.Iterator;
import java.util.Map.Entry;
import java.util.Set;
import java.util.TreeMap;

 * @author fkabakci
public class StringFrequency {
	private String text;

	public StringFrequency(String text) {
		this.text = text;

	public int count(String appear) {
		int counter = 0;
		int length = text.length();
		int alength = appear.length();

		for (int i = 0; i < length + 1 - alength; i++) {
			if (text.substring(i, i + alength).equals(appear))
		return counter;
	public void listFrequencyForLetters() {
		TreeMap<Character, Integer> alphaMap = new TreeMap<Character, Integer>();
		for (char ch : text.toCharArray()) {
			if (!alphaMap.containsKey(ch)) {
				if (Character.isLetter(ch)) {
					int n = count(String.valueOf(ch));
					alphaMap.put(ch, n);

		Set<Entry<Character, Integer>> alphaSet = alphaMap.entrySet();
		Iterator<Entry<Character, Integer>> it = alphaSet.iterator();
		while (it.hasNext()) {
			Entry<Character, Integer> node = it.next();
			char c = node.getKey();
			int n = node.getValue();
			System.out.println("The character " + c + " has occured for " + n + " times");

	public static void main(String[] args) {
		final String text = "Java is a object oriented programming language. We can create objects in Java !!";
		StringFrequency str = new StringFrequency(text);

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