Java – Count and print number of repeated character occurrences in a String

In this article, we will count and print number of repeated character occurrences in a String i.e.;

1. Counting & printing in a String:

  • Number of repeated character occurrences
  • Along with its count

Note:- Same example is implemented using Java 1.8 version and Stream, check Java 8 – Count and print number of repeated character occurrences in a String

1.1 Steps for counting repeated character occurrences:

  1. Create empty HashMap of type Character & Integer
  2. Convert String into character[] array using toCharArray() method of String class
  3. Iterate through character[] array
  4. Leave blank spaces in between 2 words in a String sentence
  5. Check whether particular character present in the HashMap using containsKey(k) method of Map interface
  6. If it contains, then increase the count value by 1 using put(K, V) method of Map interface
  7. Otherwise insert using put() method of Map with count value as 1
  8. Get keySet() for iterating through Map
  9. Finally, print character[] array using for-each loop
  10. Code sorting logic for printing count value in descending order using Comparator interface
  11. Again print after sorting

ReadCountPrintRepeatedCharacterOccurencesInString.java

package in.bench.resources.count.print.occurences;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;

public class ReadCountPrintRepeatedCharacterOccurencesInString {

	public static void main(String[] args) {

		// sample test string
		String testStr = "Spring and Hibernate";

		// invoke to count & print for supplied file
		countAndPrintRepeatedCharacterOccurences(testStr);
	}

	/**
	 * this method is used
	 * to count number repeated word occurrences
	 * @param fileName
	 */
	public static void countAndPrintRepeatedCharacterOccurences(
			String strContent) {

		// Step 1: create Map of Character-Integer
		Map<Character, Integer> mapOfRepeatedChar =
				new HashMap<Character, Integer>();

		// Step 2: convert String into character-array
		// using toCharArray() method
		char[] chArray = strContent.toCharArray();

		// Step 3: iterate through char[] array
		for(char ch : chArray) {

			// Step 4: leave spaces
			if(ch != ' '){

				// Step 5: check
				// whether Map contains particular character
				if(mapOfRepeatedChar.containsKey(ch)){

					// Step 6: If contains,
					// increase count value by 1
					mapOfRepeatedChar.put(ch,
							mapOfRepeatedChar.get(ch) + 1);
				}
				else {

					// Step 7: otherwise, make a new entry
					mapOfRepeatedChar.put(ch, 1);
				}
			}
		}

		System.out.println("Before sorting : \n");
		System.out.println("Char" + "\t" + "Count");
		System.out.println("====" + "\t" + "=====");

		// Step 8: get keySet() for iteration
		Set<Character> character = mapOfRepeatedChar.keySet();

		// Step 9: print word along with its count
		for(Character ch : character) {
			System.out.println(ch
					+ "\t" + mapOfRepeatedChar.get(ch));
		}

		// Step 10: Sorting logic by invoking sortByCountValue()
		Map<Character, Integer> wordLHMap = sortByCountValue(
				mapOfRepeatedChar);

		System.out.println("\n\nAfter sorting"
				+ " in descending order of count : \n");
		System.out.println("Char" + "\t" + "Count");
		System.out.println("====" + "\t" + "=====");

		// Step 11: Again print after sorting
		for(Map.Entry<Character, Integer> entry :
			wordLHMap.entrySet()){
			System.out.println(entry.getKey()
					+ "\t" + entry.getValue());
		}
	}

	/**
	 * this method sort acc. to count value
	 * @param mapOfRepeatedWord
	 * @return
	 */
	public static Map<Character, Integer> sortByCountValue(
			Map<Character, Integer> mapOfRepeatedWord) {

		// get entrySet from HashMap object
		Set<Map.Entry<Character, Integer>> setOfWordEntries =
				mapOfRepeatedWord.entrySet();

		// convert HashMap to List of Map entries
		List<Map.Entry<Character, Integer>> listOfwordEntry =
				new ArrayList<Map.Entry<Character, Integer>>(
						setOfWordEntries);

		// sort list of entries using Collections.sort(ls, cmptr);
		Collections.sort(listOfwordEntry,
				new Comparator<Map.Entry<Character, Integer>>() {

			@Override
			public int compare(Entry<Character, Integer> es1,
					Entry<Character, Integer> es2) {
				return es2.getValue().compareTo(es1.getValue());
			}
		});

		// store into LinkedHashMap for maintaining insertion
		Map<Character, Integer> wordLHMap =
				new LinkedHashMap<Character, Integer>();

		// iterating list and storing in LinkedHahsMap
		for(Map.Entry<Character, Integer> map : listOfwordEntry){
			wordLHMap.put(map.getKey(), map.getValue());
		}

		return wordLHMap;
	}
}

Output:

Before sorting : 

Char	Count
====	=====
p	1
a	2
r	2
b	1
S	1
d	1
t	1
e	2
g	1
H	1
i	2
n	3

After sorting in descending order of count : 

Char	Count
====	=====
n	3
a	2
r	2
e	2
i	2
p	1
b	1
S	1
d	1
t	1
g	1
H	1

Note: Stop at Step 9, if there is no business requirements for sorting either way (ascending or descending)

2. Reading from file in Java 1.7 version:

  • In the above example, we counted repeated words from String content
  • Similarly, we can read file from local drive location and count number of repeated words
  • While doing so, we need to provide catch block with FileNotFoundException and IOException for exception raised, as we are dealing with files
  • We will use try-with-resources statement introduced in Java 1.7 version, as it handles automatic resource management (ARM) implicitly i.e.; auto-closing of opened resources without explicit closing inside finally block after necessary null-safety checks
  • Thus, it improves readability of the code by reducing number of lines of code

Sample text file:

ReadPrintCharFromFileInJava7.java

package in.bench.resources.count.print.occurences;

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;

public class ReadPrintCharFromFileInJava7 {

	public static void main(String[] args) {

		// invoke to count &amp; print for supplied file
		countAndPrintRepeatedCharacterOccurences("D://WORKSPACE/"
				+ "TEST_WORKSPACE/Java_8_Project/BRN2.txt");
	}

	/**
	 * this method is used
	 * to count number repeated word occurrences
	 * @param fileName
	 */
	public static void countAndPrintRepeatedCharacterOccurences(
			String fileName) {

		// local variables
		String line = "";

		// Step 1: create Map of Character-Integer
		Map<Character, Integer> mapOfRepeatedChar =
				new HashMap<Character, Integer>();

		// Step A: Read file using try-with-resources statement
		try(BufferedReader bufferedReader =
				new BufferedReader(new FileReader(fileName))) {

			// Step B: Read line from file
			while ((line = bufferedReader.readLine()) != null) {

				// Step 2: convert String into character-array
				// using toCharArray() method
				char[] chArray = line.toCharArray();

				// Step 3: iterate through char[] array
				for(char ch : chArray) {

					// Step 4: leave spaces
					if(ch != ' '){

						// Step 4.1: convert all,
						// char into upper case, before comparison
						char upperChar= Character.toUpperCase(ch);

						// Step 5: check
						// whether Map contains same character
						if(mapOfRepeatedChar
								.containsKey(upperChar)) {

							// Step 6: If contains,
							// increase count value by 1
							mapOfRepeatedChar.put(upperChar,
									mapOfRepeatedChar.get(
											upperChar) + 1);
						}
						else {

							// Step 7: otherwise, make a new entry
							mapOfRepeatedChar.put(upperChar, 1);
						}
					}
				}
			}

			System.out.println("Before sorting : \n");
			System.out.println("Char" + "\t" + "Count");
			System.out.println("====" + "\t" + "=====");

			// Step 8: get keySet() for iteration
			Set<Character> character = mapOfRepeatedChar.keySet();

			// Step 9: print word along with its count
			for(Character ch : character) {
				System.out.println(ch
						+ "\t" + mapOfRepeatedChar.get(ch));
			}

			// Step 10: Sorting
			// provide logic by invoking sortByCountValue();
			Map<Character, Integer> wordLHMap = sortByCountValue(
					mapOfRepeatedChar);

			System.out.println("\n\nAfter sorting"
					+ " in descending order of count : \n");
			System.out.println("Char" + "\t" + "Count");
			System.out.println("====" + "\t" + "=====");

			// Step 11: Again print after sorting
			for(Map.Entry<Character, Integer> entry :
				wordLHMap.entrySet()){
				System.out.println(entry.getKey()
						+ "\t" + entry.getValue());
			}
		}
		catch (FileNotFoundException fnfex) {
			fnfex.printStackTrace();
		}
		catch (IOException ioex) {
			ioex.printStackTrace();
		}
	}

	/**
	 * this method sort acc. to count value
	 * @param mapOfRepeatedWord
	 * @return
	 */
	public static Map<Character, Integer> sortByCountValue(
			Map<Character, Integer> mapOfRepeatedWord) {

		// get entrySet from HashMap object
		Set<Map.Entry<Character, Integer>> setOfWordEntries =
				mapOfRepeatedWord.entrySet();

		// convert HashMap to List of Map entries
		List<Map.Entry<Character, Integer>> listOfwordEntry =
				new ArrayList<Map.Entry<Character, Integer>>(
						setOfWordEntries);

		// sort list of entries using Collections.sort(ls, cmptr);
		Collections.sort(listOfwordEntry,
				new Comparator<Map.Entry<Character, Integer>>() {

			@Override
			public int compare(Entry<Character, Integer> es1,
					Entry<Character, Integer> es2) {
				return es2.getValue().compareTo(es1.getValue());
			}
		});

		// store into LinkedHashMap for maintaining insertion
		Map<Character, Integer> wordLHMap =
				new LinkedHashMap<Character, Integer>();

		// iterating list and storing in LinkedHahsMap
		for(Map.Entry<Character, Integer> map : listOfwordEntry) {
			wordLHMap.put(map.getKey(), map.getValue());
		}

		return wordLHMap;
	}
}

Output:

Before sorting : 

Char	Count
====	=====
A	6
B	4
C	3
E	2
H	3
I	2
K	4
L	4
M	2
N	5
P	1
S	5
T	2
Y	1

After sorting in descending order of count : 

Char	Count
====	=====
A	6
N	5
S	5
B	4
K	4
L	4
C	3
H	3
E	2
I	2
M	2
T	2
P	1
Y	1

Note: Stop at Step 9, if there is no business requirements for sorting either way (ascending or descending)

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Happy Coding !!
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