Stringbuilder java

Question

I'm trying to store a string and determine whether it is a uppercase/lowercase letter or number, If the character is a lower case letter, redisplay the character in upper case, if the character is a upper case letter, redisplay the character in lower case if the character is a digit, display it as an asterisk. I could make it with the numbers but if I include .toString().toLowerCase() or .toUpperCase() for the letters the program keeps looping. What should I do?

public class CharacterArray {
    public static void main(String[] args) {
        StringBuilder input = new StringBuilder("800 Test St NY");
        for (int i = 0; i < input.length(); i++) {
            System.out.println(input.charAt(i));

            if(Character.isDigit(input.charAt(i))){
                input.replace(i,i+1,"*");
            }
            else if(Character.isUpperCase(input.charAt(i))) {
                input.replace(i, i+1,input.toString().toLowerCase());
            }
            else if(Character.isLowerCase(input.charAt(i))) {
                input.replace(i, i+1,input.toString().toUpperCase());
            }
            System.out.println(input);
        }
    }
 }

Is there a reason you're using StringBuilder and not just String? — Roddy of the Frozen Peas
– Roddy of the Frozen Peas, Commented Sep 18, 2014 at 21:41

khelwood · Accepted Answer · 2014-09-18 21:53:05Z

2

When you do this:

input.replace(i, i+1, input.toString().toLowerCase());

you are replacing one character with the whole of your string (in lower case), making input longer and longer so you'll never get to the end of it.

Instead:

input.replace(i, i+1, input.substring(i,i+1).toLowerCase());

Similarly where you convert to upper case.

Edit: fixed passing wrong argument type to replace.

Volune's answer looks better still. Use that.

edited Sep 18, 2014 at 21:53

answered Sep 18, 2014 at 21:44

khelwood

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4 Comments

Volune Over a year ago

Character.toLowerCase(input.charAt(i)) is a char and not accepted by the replace method. Try input.substring(i, i + 1).toLowerCase() instead.

PM 77-1 Over a year ago

I believe that both beginning and ending index should be i (the same). replace() method specifies that both indexes are inclusive.

user3764862 Over a year ago

The method replace(int, int, String) in the type StringBuilder is not applicable for the arguments (int, int, char) :/

khelwood Over a year ago

@PM77-1 no it doesn't. It says the end is exclusive.

MarGar · Accepted Answer · 2014-09-19 01:13:16Z

2

Since you want to replace only one character, you should use StringBuilder#setCharAt:

if (Character.isDigit(input.charAt(i))) {
    input.setCharAt(i, '*');
} else if (Character.isUpperCase(input.charAt(i))) {
    input.setCharAt(i, Character.toLowerCase(input.charAt(i)));
} else if (Character.isLowerCase(input.charAt(i))) {
    input.setCharAt(i, Character.toUpperCase(input.charAt(i)));
}

This way you know you won't change the length of the string.

edited Sep 19, 2014 at 1:13

MarGar

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answered Sep 18, 2014 at 21:49

Volune

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Comments

Jean Logeart · Accepted Answer · 2014-09-18 21:46:30Z

0

Using StringUtils.swapCase:

String res = StringUtils.swapCase(original).replaceAll("\\d","*");

answered Sep 18, 2014 at 21:46

Jean Logeart

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Comments

user3487063 · Accepted Answer · 2014-09-18 21:55:31Z

-1

You need to use Character#toUpperCase and Character#toLowerCase

public static void main(String[] args){


            StringBuilder input = new StringBuilder("800 Test St NY");
            for (int i = 0; i < input.length(); i++) {
                System.out.println(input.charAt(i));

                if(Character.isDigit(input.charAt(i))){
                    input.replace(i,i+1,"*");
                }
                else if(Character.isUpperCase(input.charAt(i))) {
                    input.replace(i, i+1,Character.toString(Character.toLowerCase(input.charAt(i))));
                }
                else if(Character.isLowerCase(input.charAt(i))) {
                    input.replace(i, i+1,Character.toString(Character.toUpperCase(input.charAt(i))));
                }
                System.out.println(input);
            }
        }

prints (the output of above code:)

8
*00 Test St NY
0
**0 Test St NY
0
*** Test St NY

*** Test St NY
T
*** test St NY
e
*** tEst St NY
s
*** tESt St NY
t
*** tEST St NY

*** tEST St NY
S
*** tEST st NY
t
*** tEST sT NY

*** tEST sT NY
N
*** tEST sT nY
Y
*** tEST sT ny

edited Sep 18, 2014 at 21:55

answered Sep 18, 2014 at 21:50

user3487063

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6 Comments

user3487063 Over a year ago

Why downvote? this is working, please run the code and see if its failing and then downvote.

user3487063 Over a year ago

@user3764862, thanks for checking. If you believe its working please upvote. :)

user3764862 Over a year ago

I don't have enough reputation to vote but I really appreciate your help :)

MarGar Over a year ago

It is the wrong output. Use one of the answers that was upvoted to get the correct output.

MarGar Over a year ago

@user3487063, you are correct. The mistake was in Volune's solution. Instead of converting lower to upper, he tried to convert lower to lower in his last else if statement. My apologies for comparing the wrong output to yours.

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