StringBuilder substring and reverse - Java

Question

Can anyone help me write me a Java method that takes a substring of a string, reverses it and prints the outcome?

I'm guessing a StringBuilder is better than String but my issue is StringBuilder.substring() returns a String. To continue using StringBuilder I'd need to create a new StringBuilder object to do the StringBuilder.reverse() part.

Anyone a better solution to this?

    public static void main(String[] args) {
    StringBuilder sb = new StringBuilder("abcdefgh");

    sb = new StringBuilder(sb.subSequence(2, 5));

    sb.reverse(); 
    System.out.println(sb.toString());
}

PSR · Accepted Answer · 2013-04-08 11:08:26Z

1

You can use this

public String reverseString(String normalString) {
   StringBuilder sb = new StringBuilder();
   for(int i = normalString.length() - 1; i >= 0; --i)
     sb.append(normalString.charAt(i));
   return sb.toString();
 }

edited Apr 8, 2013 at 11:08

answered Apr 8, 2013 at 10:39

PSR

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3 Comments

TheCoder Over a year ago

The latter doesn't work. I'd need to create a new StringBuilder object to then reverse.

PSR Over a year ago

@heyya99 if you got the solution with my answer please accept this as anser

TheCoder Over a year ago

I think it's overly complicated. I think I could use a String to make it less complicated.

Achintya Jha · Accepted Answer · 2013-04-08 11:17:22Z

0

You can try something like this:

String s = "Achintya";
List<String> myList = new ArrayList<String>(Arrays.asList(s.split("")));
Collections.sort(myList, Collections.reverseOrder());
System.out.println(myList);

answered Apr 8, 2013 at 11:17

Achintya Jha

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Comments

BlackBox · Accepted Answer · 2013-04-08 12:06:53Z

0

If your desire is to have users input the start and end indicies of the non-reversed String, you could achieve this easily by re-mapping the index values.

Below is a working example of 1 StringBuilder as you asked for:

public static void main(String[] args) {
    final StringBuilder sb = new StringBuilder("abcdefgh");
    final int startIndex = 2;
    final int endIndex = 5;

    sb.reverse();
    final String output = substring(sb.toString(), startIndex, endIndex);
    System.out.println("Result: " + output);
}

//Retrieve the substring of a reversed string
private static String substring(String input, int start, int end) {
    start = map(start, 0, input.length(), input.length(), 0);
    end = map(end, 0, input.length(), input.length(), 0);

    String substring = input.substring(end, start);
    return substring;
}

//Map value from the min,max range, to the new minRange-maxRange range.
private static int map(float value, float min, float max, float minRange, float maxRange) {
    return Math.round(minRange + (maxRange - minRange) * ((value - min) / (max - min)));
}

answered Apr 8, 2013 at 12:06

BlackBox

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2 Comments

TheCoder Over a year ago

Thanks but I'm being marked on this and I need it to be as simple as possible. Your solution's complexity would count against me I fear.

BlackBox Over a year ago

It is quite simple really, its just calculating the indices in relation to the reverse. The simplest is yours, but instead of the first String builder you just use: String input = "abcdefgh";

Glad Born · Accepted Answer · 2015-03-28 15:11:46Z

0

Your answer is good enough. If you want to use substring method this too will work,

public static void main(String[] args) 
{
StringBuilder revWord = new StringBuilder("abcdefgh".substring(2,5));
revWord.reverse(); 
System.out.println(revWord);
}

answered Mar 28, 2015 at 15:11

Glad Born

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Comments

K246 · Accepted Answer · 2015-06-26 00:06:36Z

0

Simply reverse your operations:

StringBuilder sb2 = new StringBuilder("abcdefgh");
sb2.reverse();
System.out.println(sb2.subSequence(sb2.length()-5, sb2.length()-2));

answered Jun 26, 2015 at 0:06

K246

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