Java parenthesis replacement with empty string

Question

Why doesn't the first line replace "(" with an empty string , while the second one does?

 public static void main(String []args){
     String a="This(rab)(bar)";
     a=a.replace("\\(",""); //First
     String b=a.replaceFirst("\\(","");//Second
    System.out.println(a + " "+b);
 }

Answer 1

There is a difference between replace and replaceFirst. If your IDE shows you the method signatures, you'll see:

See how replace accepts a plain old target whereas replaceFirst accepts a regex?

"\\(" is a regex that means "a single open parenthesis". replace doesn't treat the strings you pass in as regexes. It will simply try to find a backslash followed by an open parenthesis, which does not exist in your string.

If you want to use replace, just use "(".

Answer 2

For replace to work you should write:

a=a.replace("(",""); //First

or use replaceAll if you want to pass a regex:

a=a.replaceAll("\\(",""); //First

replace accepts a sequence of characters to replace:

public String replace(CharSequence target, CharSequence replacement)

Therefore, in your case it attempts to replace the 3 characters "\(", not just the single character "(".