Remove doubled letter from a string using java

Question

I need to remove a doubled letter from a string using regex operations in java. Eg: PRINCEE -> PRINCE APPLE -> APLE

Answer 1

This can be done simply by iterating over the String instead of having to resort to regexes.

StringBuilder ret=new StringBuilder(text.length());

if (text.length()==0) return "";
ret.append(text.charAt(0));
for(int i=1;i<text.length();i++){
  if (text.charAt(i)!=text.charAt(i-1))
    ret.append(text.charAt(i));
}

return ret.toString();

Answer 2

If you want to replace just duplicate ("AA"->"A", "AAA" -> "AA") use

public String undup(String str) {
  return str.replaceAll("(\\w)\\1", "$1");
}

To replace triplicates etc use: str.replaceAll("(\\w)\\1+", "$1");

To replace only a single dupe is a long string (AAAA->AAA, AAA->AA) use: str.replaceAll("(\\w)(\\1+)", "$2");

Answer 3

String s = "...";
String replaced = s.replaceAll( "([A-Z])\\1", "$1" );

Answer 4

Simple Solution (remove duplicate characters)

Like this:

final String str = "APPLEE";
String replaced = str.replaceAll("(.)\\1", "$1");
System.out.println(replaced);

Output:

APLE

Not just any Chracters, Letters only

As @Jim comments correctly, the above matches any double character, not just letters. Here are a few variations that just match letters:

// the basics, ASCII letters. these two are equivalent:
str.replaceAll("([A-Za-z])\\1", "$1");
str.replaceAll("(\\p{Alpha})\\1", "$1");

// Unicode Letters
str.replaceAll("(\\p{L})\\1", "$1");

// anything where Character.isLetter(ch) returns true
str.replaceAll("(\\p{javaLetter})\\1", "$1");

References:

For additional reference:

1. Character.isLetter(ch) (javadocs)
2. any method in Character of the form Character.isXyz(char) enables a pattern named \p{javaXyz} (mind the capitalization). This mechanism is described in the Pattern javadocs
3. Unicode blocks and categories can also be matched with the \p and \P constructs as in Perl. \p{prop} matches if the input has the property prop, while \P{prop} does not match if the input has that property. This mechanism is also described in the Pattern javadocs