StringBuilder.insert() not changing output

Question

I'm trying to make a short program that converts any string into T H I S F O N T.

For example: "This is a test sentence" turns into "T H I S I S A T E S T S E N T N C E"

I have a StringBuilder inside a while loop, but using finale.insert(i, '\t'); doesn't work.

import java.util.Scanner;

public class Executable {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        String x;
        int i = 0;

        System.out.print("Input text here: ");
        x = input.nextLine();

        StringBuilder finale = new StringBuilder(x.toUpperCase());

        while(i > finale.length()) {
            if(finale.substring(i, i) == " ") {
                i += 2;

                finale.insert(i, '\t');
            }
        }

        System.out.println(finale);

    }
}

Any help?

Answer 1

You are comparing strings with ==. Never do that; use equals instead.

For future readers: this job can be done elegantly using Java 8 Streams:

String result = str.chars()
    .filter(i -> i != ' ')
    .mapToObj(t -> (char) t)
    .map(Character::toUpperCase)
    .map(Character::valueOf)
    .collect(Collectors.joining(" ");

Answer 2

You have a few issues with your code. Before I present an implementation that works, let's look at those other issues.

1. Your while loop checks if i > finale.length(). Since i = 0 the while loop never has a chance to begin.
2. You are comparing strings using == and this is not correct. == is used to confirm two objects are equal, not the value of two strings. You would need to use string.equals() instead.
3. You're doing too much in your loop anyway. Using a simple for loop can accomplish the goal quite simply.

Here is a new loop you can use instead of what you have:

for (int i = 1; i < finale.length(); i++) {
    finale.insert(i++, " ");
}

The output: T H I S F O N T

---

For those unfamiliar with for loops, here's a very simple breakdown of how the above is structured.

The for loop is defined in three parts:

for (variable_to_increment; repeat_until_this_condition_is_met; modify_variable_on_each_iteration) {
    // Code to be executed during each pass of the loop
}

• First, we define a variable that we can track on each loop: int i = 1. By setting i = 1, we are going to skip the first character in the string.
• The next statement, i < finale.length() means that we want to keep repeating this loop until we reach the length of our string. For example, if the string is 5 characters long and we've run the loop 4 times, i now equals 5 and is no longer less than the string's length, so the loop ends.
• The last part is i++. This tells Java what we want to do with i after each loop. In this case, we want to increment the value by 1 each time the loop repeats.
• Everything inside the brackets is, obviously, the code we want to execute on each loop.

Answer 3

Some issues with your code (see inline comments):

import java.util.Scanner;

public class Executable {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        String x;
        int i = 0;

        System.out.print("Input text here: ");
        x = input.nextLine();

        StringBuilder finale = new StringBuilder(x.toUpperCase());

        while(i > finale.length()) { // this condition is incorrect. Initially
                                     // this condition will always be false
                                     // if you input some sentence. It should be 
                                     // i < finale.length()
            if(finale.substring(i, i) == " ") { // here preferably you should use
                                                // equals method to compare strings
                i += 2;
                // you are only incrementing the i if the ith
                // substring equals " ". Firstly, substring(i,i)
                // will return empty string because the second argument
                // is exclusive
                finale.insert(i, '\t');
            }
        }

        System.out.println(finale);

    }
}

If you want to have an alternate method (not very optimal) for doing what you want to do, you can try the following approach:

import java.util.Scanner;

public class Executable {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        String x;
        int i = 0;

        System.out.print("Input text here: ");
        x = input.nextLine();

        String finale = x.toUpperCase().replaceAll(" ","").replaceAll("", " ");



        System.out.println(finale);

    }
}

First, convert the string to uppercase --> then remove all spaces between the words --> then insert spaces between all letters. The code line which does this is,

String finale = x.toUpperCase().replaceAll(" ","").replaceAll("", " ");

Here is a sample run:

Input text here: This is a sentence
 T H I S I S A S E N T E N C E 

Answer 4

Use a for loop since you know the number of iterations:

    Scanner input = new Scanner(System.in);

    String x;

    System.out.print("Input text here: ");
    x = input.nextLine();

    StringBuilder finale = new StringBuilder(x.toUpperCase());

    int len = finale.length();
    for (int i = 1; i < 2 * len; i+=2 ) {
        finale.insert(i, '\t');
    }

    System.out.println(finale);

Answer 5

1. The correct way with your method would be, just increment until you have twice the size of the initial String

   while (i < x.length() * 2) {
       finale.insert(i, '\t');
       i += 2;
   }
   

2. An easier way would be with a classic for-loop:

   StringBuilder finale = new StringBuilder();
   for (char c : x.toUpperCase().toCharArray()) {
       finale.append(c).append('\t');
   }
   

Answer 6

You're saying while i>finale.length() but i is initialized as 0. You never enter the while loop.