Flip characters in java

Question

so by the title, I am trying to flip characters from one value, to the opposite value. For example, - would become +, and + would become minus. These are the only 2 values right now, but I was wondering how I should go about this. So far I have this

public static String flip(String s, int index) {
    System.out.print("suuuh");
    String k = s;
    ArrayList<Character> array = new ArrayList<>();
    for (Character c : k.toCharArray()) {
        array.add(c);
        System.out.print(c);
    }
    for (int i = 0; i > index; i++) {
        if (array.get(i) == '-') {

            array.set(i, '+');
        } else {
            array.set(i, '+');
        }

    }
    StringBuilder builder = new StringBuilder();
    for (Character c : array) {
        builder.append(c.toString());
    }
    return builder.toString();
}

but it does not flip the + to a - or vice versa.

There is no inherent meaning of "opposite" for the text characters "+", "-" or "A", "B" or "C". SUGGESTION: create a table of "opposites" (e.g. with a character array). — paulsm4, Apr 09 '16 at 23:52
Possible duplicate of [How do I compare strings in Java?](http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — Smutje, Apr 09 '16 at 23:53
If you read it, I stated that "these are th only 2 values right now." — Kobey Rafferty, Apr 09 '16 at 23:54
Why build a `ArrayList` from the `char[]` returned by `toCharArray()`? Just update the `char[]`, then construct a new string from it using `new String(char[])`. — Andreas, Apr 09 '16 at 23:54
After the `else` the line should be `array.set(i, '-');`. Otherwise, both `.set()` methods change to `+`. — Sci Prog, Apr 09 '16 at 23:55

Paul Boddington · Accepted Answer · 2016-04-10T00:02:20.027

1

Your basic approach is correct, although I would recommend a HashMap to store the opposites.

The reason your code does nothing is because

for (int i = 0; i > index; i++) {

should be something else, probably

for (int i = 0; i < array.size(); i++) {

At the moment, the loop is terminating immediately.

Also, the else should be

array.set(i, '-');

Another improvement is that there is no point using a List<Character> for this; you can use the char returned by toCharArray() directly.

edited Apr 10 '16 at 00:02

answered Apr 09 '16 at 23:58

Paul Boddington

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Good catch. And the `else` should be `array.set(i, '-');`, as noted by @SciProg in a comment. – Andreas Apr 10 '16 at 00:00
@Andreas Thanks. Do you know what `index` is for? I don't want to correct this code incorrectly. – Paul Boddington Apr 10 '16 at 00:01
And since you recommend improvements, I'd recommend using the `char[]` returned by `toCharArray()` directly, instead of boxing all the characters into a `List`. – Andreas Apr 10 '16 at 00:02
1

Paul, no I don't. The `print("suuuh")` is also a bit weird. ;-) – Andreas Apr 10 '16 at 00:04
@KobeyRafferty Glad we could help! – Paul Boddington Apr 10 '16 at 00:05

Flip characters in java

1 Answers1