Swapping Characters in a String in Java

Question

Given the above excerpt from a Java code, I need to modify the code such that it could recursively swap pairs of the content of the string variable, "locationAddress". Please note that the variable, "locationAddress", contains a string of characters, say, abcdefghij. I wish to swap "abcdefghij" in pairs such that the result will be "badcfehgji".

Please kindly assist with the necessary modification to the above Java code excerpt to make it recursively swap pairs of characters in the string variable, "locationAddress".

public void format(DataObject dataSource) throws Exception {
    String locationAddress = dataSource.getValueAsString("Location-Address").substring(4);
    if (dataSource.parameterExists("Location-Address")) {
        dataSource.setParameter("Parameter-Type","400");
        dataSource.setParameter("Parameter-Value", locationAddress);
    }    
}

You should try yourself, then post your code here and guys will help you — Milad Aghamohammadi
– Milad Aghamohammadi, Commented Nov 1, 2018 at 10:09

Tim Biegeleisen · Accepted Answer · 2018-11-01 09:54:37Z

3

Here is a very simple way to do this using regex replacement in Java:

String input = "abcdefghij";
input = input.replaceAll("(.)(.)", "$2$1");
System.out.println(input);

badcfehgji

The idea is to walk down the string, starting at the beginning, capturing two characters at a time, in two different capture groups. Then, just swap those two captured characters in the replacement.

answered Nov 1, 2018 at 9:54

Tim Biegeleisen

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2 Comments

Sweeper Over a year ago

That's a nice trick! The idea of using a regex never crossed my mind! I was thinking more along the lines of StringBuilder.

Tim Biegeleisen Over a year ago

@Sweeper ... which is probably the direction you'd go in if you really needed this to run lightning fast, or as fast as possible. Regex has a big overhead. But, for a one off need, my answer is suitable.

Sweeper · Accepted Answer · 2018-11-01 10:09:12Z

1

Here's one solution with StringBuilder:

public static String swapAdjacentPairs(String s) {
    StringBuilder sb = new StringBuilder(s);
    // divide 2 and then multiply by 2 to handle cases where the string length is odd
    // we always want an even string length
    // also note the i += 2
    for (int i = 0 ; i < (s.length() / 2 * 2) ; i += 2) {
        swapAdjacent(sb, i);
    }
    return sb.toString();
}

private static void swapAdjacent(StringBuilder sb, int index) {
    char x = sb.charAt(index);
    sb.setCharAt(index, sb.charAt(index + 1));
    sb.setCharAt(index + 1, x);
}

Usage:

System.out.println(swapAdjacentPairs("abcdefghi"));

answered Nov 1, 2018 at 10:09

Sweeper

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Comments

LuCio · Accepted Answer · 2018-11-01 11:47:42Z

0

A solution using Stream:

String input = "abcdefghijk";
String swapped = IntStream.range(0, input.length())
        .map(i -> i % 2 == 0 ? i == input.length() - 1 ? i : i + 1 : i - 1)
        .mapToObj(input::charAt)
        .map(String::valueOf)
        .collect(Collectors.joining());
System.out.println(swapped); // badcfehgjik

The swapping is driven by the index i. If i is even and there is a next (i+1) character then it's used. If i is odd then the previous (i-1) character is used.

edited Nov 1, 2018 at 11:47

answered Nov 1, 2018 at 11:07

LuCio

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