replaceFirst does not work, but replace works on the exact same input?

Question

I am writing a program where a portion of it needs to replace part of the string without deleting duplicates so I am using replaceFirst() which is not working properly.

INPUT:

lock: "O_2_^-^"
str:  " O_2_^-^ " 

CODE:

System.out.println(str);
System.out.println(lock);
System.out.println(str.contains(lock));
str = str.replaceFirst(lock, "");
System.out.println(str);

OUTPUT:

 O_2_^-^ 
O_2_^-^
true
 O_2_^-^ 

The above is real output from my program. Though the replace() method will not work for my current situation I did test it and the output is compeletely different, as in correct.

INPUT:

lock: "O_2_^-^"
str:  " O_2_^-^ " 

CODE:

System.out.println(str);
System.out.println(lock);
System.out.println(str.contains(lock));
str = str.replace(lock, "");
System.out.println(str);

OUTPUT:

 O_2_^-^ 
O_2_^-^
true
  //empty line of output because string was detected and removed.

I have tried everything outside of writing my own replaceFirst() method, if anyone has any advice or input that'd be great. Thanks!

Answer 1

Since replaceFirst's 1st parameter is assumed to be a regex, you need to escape special characters. If you do not know beforehand what lock is going to be (example coming from user-input), you can use Pattern.quote(lock) to escape it.

See, also, this short demo.

Answer 2

replaceFirst(String regex, String replacement) takes regex as a parameter, use this:

String lock = "O_2_\\^-\\^";

---

String lock = "O_2_\\^-\\^";
String str = " O_2_^-^ "; 
System.out.println(str);
System.out.println(lock);
System.out.println(str.contains(lock));
str = str.replaceFirst(lock, "");
System.out.println(str);

OUTPUT:

O_2_^-^ 
O_2_\^-\^
false