StringModifier - Reverses a string and returns information about it

Question

I have been coding in Java for about a month now and I'm seeking advice for my program on things I can improve. This project was mainly made for me to incorporate all the new things I learned and utilize them effectively. I appreciate any feedback :).

About the program itself, it takes in a string and reverses it. It also counts the amount of characters (spaces, numbers, letters, and other characters) and it checks if the typed string is a palindrome or not.

Main class

public class Main {
 
 public static void main(String[] args) {
 Application application = new Application();
 
 application.printInstructions();
 application.programLoop();
 application.printSeparator(); // Prints a separator before the program terminates.
 }
}

Application class

import java.util.Scanner;
public class Application {
 Scanner userInput = new Scanner(System.in);
 String definedString;
 // Main function for reversing the string.
 private String reverseString(String string) {
 StringBuilder stringBuilder = new StringBuilder();
 char[] charArray = string.toCharArray();
 for (int i = string.length() - 1; i >= 0; i--) {
 stringBuilder.append(charArray[i]);
 
 }
 
 return stringBuilder.toString();
 }
 // Processes the output and prints it out.
 private void processInput() {
 
 printSeparator();
 System.out.println("Reversed String: " + reverseString(definedString));
 printSeparator();
 
 countCharacters(definedString);
 isPalindrome();
 programLoop();
 
 }
 // Main program loop.
 public boolean programLoop() {
 System.out.print("-: ");
 definedString = userInput.nextLine();
 
 // If the input isn't the break command, it processes and prints out the results.
 while (!definedString.equals("!break")) {
 processInput();
 
 }
 
 return false;
 
 }
 // Prints starting instructions.
 public void printInstructions() {
 System.out.println("StringModifier - Reverses a string and returns information about it.");
 System.out.println("Type '!break' to exit");
 
 }
 // Counts the amount of characters in the reversed string.
 private void countCharacters(String string) {
 char[] charArray = string.toCharArray();
 int letters = 0;
 int numbers = 0;
 int spaces = 0;
 int other = 0;
 for (int i = 0; i < string.length(); i++) {
 if (Character.isSpaceChar(charArray[i])) {
 spaces++;
 } else if (Character.isDigit(charArray[i])) {
 numbers++;
 } else if (Character.isLetter(charArray[i])) {
 letters++;
 } else {
 other++;
 }
 }
 
 System.out.println("Spaces: " + spaces);
 System.out.println("Numbers: " + numbers);
 System.out.println("Letters: " + letters);
 System.out.println("Other: " + other);
 }
 
 // Adds a separating line.
 public void printSeparator() {
 System.out.println("—————————————————————————————————————");
 
 }
 
 // Checks if the string is a palindrome.
 public void isPalindrome() {
 
 if (definedString.equals(reverseString(definedString))) {
 System.out.println("Is a Palindrome: Yes");
 } else {
 System.out.println("Is a Palindrome: No");
 }
 }
}

Answer 1

You should rewrite your reverseString to use the built-in StringBuilder.reverse().

Your class structure is a little bit mixed up. The Application and Main classes currently have some of the same obligations. Rephrase this to, perhaps,

• a Main class that only cares about display and does your program loop
• a StringInfo class that does no integrated display in its logic methods, and has accessor functions for reversed (returning a string and not printing), isPalindrome (returning a boolean and not printing), spaceCount (returning an integer and not printing), etc.

Suggested

import java.util.Scanner;
public class Main {
 final Scanner userInput = new Scanner(System.in);
 public static void main(String[] args) {
 Main app = new Main();
 printInstructions();
 app.programLoop();
 printSeparator();
 }
 // Prints starting instructions.
 public static void printInstructions() {
 System.out.println("StringModifier - Reverses a string and returns information about it.");
 System.out.println("Type '!break' to exit");
 }
 // Main program loop.
 public void programLoop() {
 // If the input isn't the break command, it processes and prints out the results.
 while (true) {
 printSeparator();
 System.out.print("-: ");
 String definedString = userInput.nextLine();
 if (definedString.equals("!break"))
 break;
 (new StringInfo(definedString)).dump();
 }
 }
 // Adds a separating line.
 public static void printSeparator() {
 System.out.println("—————————————————————————————————————");
 }
}
public class StringInfo {
 public final String definedString;
 public StringInfo(String definedString) {
 this.definedString = definedString;
 }
 public String reversed() {
 StringBuilder builder = new StringBuilder(definedString);
 builder.reverse();
 return builder.toString();
 }
 public long nSpaces() {
 return definedString.chars().filter(ch -> Character.isSpaceChar(ch)).count();
 }
 public long nLetters() {
 return definedString.chars().filter(ch -> Character.isLetter(ch)).count();
 }
 public long nDigits() {
 return definedString.chars().filter(ch -> Character.isDigit(ch)).count();
 }
 public long nOther() {
 return definedString.chars().filter(ch -> !(
 Character.isSpaceChar(ch)
 || Character.isLetter(ch)
 || Character.isDigit(ch)
 )).count();
 }
 public boolean isPalindrome() {
 return definedString.equals(reversed());
 }
 public void dump() {
 System.out.printf("Reversed String: %s%n", reversed());
 System.out.printf("Spaces: %d%n", nSpaces());
 System.out.printf("Digits: %d%n", nDigits());
 System.out.printf("Letters: %d%n", nLetters());
 System.out.printf("Other: %d%n", nOther());
 System.out.print("Is a palindrome: ");
 if (isPalindrome()) System.out.println("yes");
 else System.out.println("no");
 }
}

• Kareem Ghazi: Thank you for your feedback! I do have one question though. Why is it preferable to use return statements instead of just printing it out from the method? My thought is to probably have flexible values which I can use anywhere in my program.
• Ralf Kleberhoff: @Kimosauraus Why prefer return over printing? Because you might want to re-use things like string reverting or character counting later in a program with a GUI, or in a web server or whatever. Make it a habit to separate information processing from input/output.
• Kareem Ghazi: Ah, I see. Thank you for your answer.