Java list index out of range

Question

In java, what is the best way to switch characters in a string while keeping the rest of the characters in their original spot. My real concern is if there's a way to deal with this index out of range error other than the following:
Let's say you want to switch the letter r with the capital E in "stringExample".

you can chunk this into "st" + "r" + "ing" + "E" + "xample"

---------------------------->(0,i)--(i,i+1)--(i+1,k)--(k,k+1)---(k+1)

then to switch "r" & "E": "st" + "E" + "ing" + "r" + "xample"

----------------------------->(0,i)--(k,k+1)--(i+1,k)--(i,i+1)---(k+1)

The only problem is if k is the last index then you need to write an if statement to catch this exception. Other than doing what I suggested before, is there a better way of switching these letters?

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Answer 1

If you're looking to just replace characters in a string, you're probably best off rebuilding your string entirely using String.substring. For your example, you'd simply need to use temporary variables to hold the letters you want to swap. For example:

String swapLetters(String str, int firstIndex, int secondIndex) {
    if (firstIndex < 0 || firstIndex >= str.length()) {
        throw new IndexOutOfBoundsException("firstIndex '" + firstIndex + "' is out of bounds.");
    } else if (secondIndex < 0 || secondIndex >= str.length()) {
        throw new IndexOutOfBoundsException("secondIndex '" + secondIndex + "' is out of bounds.");
    } else if (firstIndex >= secondIndex) {
        throw new IndexOutOfBoundsException("firstIndex isn't before secondIndex");
    }


    StringBuilder newString = new StringBuilder(str.substring(0, firstIndex));
    newString.append(str.charAt(secondIndex)).append(str.substring(firstIndex + 1, secondIndex))
             .append(str.charAt(firstIndex)).append(str.substring(secondIndex + 1));

    return newString.toString();
}

Here, even if it's the last letter the substring will just return an empty string and it'll be fine.

System.out.println("stringExample becomes " + swapLetters("stringExample", 2, 12)); //--> stringExample becomes steingExamplr
System.out.println("stringExample becomes " + swapLetters("stringExample", 2, 6)); //--> stringExample becomes stEingrxample

If you want to just replace the first instance of each letter given letters, you'd use indexOf('r') instead of charAt(2), for example.

Java list index out of range

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