Replacing multiple occurences of special characters by a single special character

Question

I want to remove multiple occurrences of special characters like \" \", \"-\", \"!\", \"_\" from my java string by a sing

Answer 1

Note that \1 is a backreference to the contents matched with the first capturing group. To actually match one or more any characters from the character class, just use a + quantifier:

[\\s!-]+

So, use

str = str.replaceAll("[\\s!-]+","_");

See IDEONE demo