用与同一索引不同的字符替换特定的索引字符

Question

I'm still very new java and find that I spend a lot of time spinning my wheels for things that may be simple. I am writing an app that takes a user entered string of text and places it into a charArray. From here, I want to use the replace method to replace the character at index 0 with the character at index 1. ( I understand that replace will change all other values in the string that have the same value as char(0).

if (input.equals(blank) || input.equals(mptee)){   
    System.out.println("You have choen to exit, Goodbye");
}

char[] stringToCharArray = input.toCharArray(); // convert string to charArray

for(char output : stringToCharArray) {
    System.out.print(output);
    //code to simplify character validation    
    Character x = input.charAt(0);       
    Character y = input.charAt(1);                  
    if( Character.isLetter(input.indexOf(0)) 
                        && ( Character.isLetter(input.indexOf(1))) ){
        input.replace(input.charAt(0),input.charAt(1));
    }
}
System.out.println(input);

Although it accepts a string, and gives the length, the character replace does not occur. I have read for days on "indexOf" , String RegEx, and much more. Any assistance would be appreciated.

Answer 1

Strings are immutable so after you call the replace method you need to assign it back to input . Change

input.replace(input.charAt(0),input.charAt(1));

to

input  = input.replace(input.charAt(0),input.charAt(1));

Answer 2

String input = new String("abcdefgh");
input = input.substring(1, 2) + input.substring(1);

gives you bbcdefgh if that is what you want?

Is it a must to convert the string to a char array and go through the for loop?
I find it a bit unnecessary since you are only working on the first & second character.

If you must convert it to a char array, what about this?

String input = new String("abcdefgh");      
char[] stringToCharArray = input.toCharArray();

if(Character.isLetter(stringToCharArray[0]) && Character.isLetter(stringToCharArray[1]))
{
    // Replace character at index 0 with character at index 1
    stringToCharArray[0] = stringToCharArray[1];
}

input = String.valueOf(stringToCharArray); // Convert back to String
System.out.println(input); // Gives you bbcdefgh

There is more than 1 way to achieve what you want, so maybe you can take a look at the String documentation?