How do I change vowels in a string in Java if a certain condition is met?

Question

How do I make it so that if the 3rd letter of the 1st string I input is found on the 2nd string, it will print the first string in all caps and change its vowels to *? If the 3rd letter is not found on the second string it will print the second string in small letters and replace all the vowels to @?

import java.io.*;
public class Program2 {
    
    public static void main(String args[]) throws IOException {
        BufferedReader data = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter the first String:");
        String first = data.readLine();
        System.out.println("Enter the second String:");
        String second = data.readLine();
        
        char a[] = first.toCharArray();
        char b[] = second.toCharArray();
        char c = first.charAt(2);
        char ch;
        String text;
        String mute;
        
        for (int w = 0; w < b.length; w++)
        {
            ch = second.charAt(w);
            if (ch == c) {                
                for (int i = 0; i < a.length; i++) {
                    if (a[i]=='a'||a[i]=='e'||a[i]=='i'||a[i]=='o'||a[i]=='u') {
                        a[i]='*'; //replaces the vowels with *
                        }            
                    text = Character.toString(a[i]);
                    System.out.print(text.toUpperCase());
            }
            }
            else if (ch != c) {
                for (int x = 0; x < b.length; x++) {
                    if (b[x]=='a'||b[x]=='e'||b[x]=='i'||b[x]=='o'||b[x]=='u') {
                        b[x]='@'; //replaces the vowels with @
                        }
                    mute = Character.toString(b[x]);
                    System.out.print(mute.toLowerCase());
                }
            }
        }
    }
}public static void main(String args[]) throws IOException {
        BufferedReader data = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter the first String:");
        String first = data.readLine();
        System.out.println("Enter the second String:");
        String second = data.readLine();
        
        char b[] = second.toCharArray();
        char c = first.charAt(2);
        char ch;
        String text;
        String mute;
        
        int x = 1;
        while (x < b.length) {
        {
            ch = second.charAt(x);
            if (ch == c) {                
                text = first.toUpperCase();
                System.out.println(text.replaceAll("[AaEeIiOoUu]", "*"));    
            }
            else if (ch != c) {
                mute = second.toLowerCase();
                System.out.println(mute.replaceAll("[AaEeIiOoUu]", "@"));
            }
        x++;    
    }
    }
}
}

somehow the code print multiple copies of the output and sometimes the second string appears even the second condition is not met

Answer 1

Your code prints out one string at each character of the second string, since it runs INSIDE the loop. So

• get rid of the loop, String.indexOf(char) does what you want
• do the string replacement outside the check to see if a character matches.

Something like:

...
if (second.indexOf(c)>-1){
   ... code for case when second string contains character
} else {
   ... code for case when second string does NOT contains character (indexOf returns -1)
}

Then, instead of using character arrays, investigate the String.replace function to simply replace some characters by others.