<p>In java, which regular expression can be used to replace these,
for example:</p>

<p>before:
aaabbb
after:
ab</p>

<p>before:
14442345 
after:
142345</p>

<p>thanks!</p>

In perl
```
```
s/(.)\1+/$1/g;
```
```
Does the trick, I assume if java has perl compatible regexps it should work too.
Edit: Here is what it means
```
```
s {
    (.)  # match any charater ( and capture it )
    \1   # if it is followed by itself 
    +    # One or more times
}{$1}gx;  # And replace the whole things by the first captured character (with g modifier to replace all occurences)
```
```
Edit: As others have pointed out, the syntax in Java would become
```
```
original.replaceAll("(.)\\1+", "$1");
```
```
remember to escape the \1