java - Replace case insenstive in string -

I have a file and I have converted that file into a string.

I have tried these two cases.

  Now when I do some string 'target' = "fo and hahah"; Target = target.rele ("furar", ""); Println (target);   
 This is giving me this output  fooBar and tooohh   
 then I tried it  
  String target123 = "FOB and even"; Target123 = target123.replace ("(I?)", ""); Println (target123);   
 And it gives me the same output: -  and also     
 
 
 or the method and regex  (? I) foobar   
  string has been replaced = target.Restore all ( "(? I) phrase", "");   
 or  
  replaced string = target.relefram ("(? I) phrase", "");   
 method  string :: change  can not be used with  regex     is