Why does String.split need pipe delimiter to be escaped?

Question

I am trying to parse a file that has each line with pipe delimited values. It did not work correctly when I did not escape the pipe delimiter in split method, but it worked correctly after I escaped the pipe as below.

private ArrayList<String> parseLine(String line) {

    ArrayList<String> list = new ArrayList<String>();

    String[] list_str = line.split("\\|"); // note the escape "\\" here

    System.out.println(list_str.length);

    System.out.println(line);

    for(String s:list_str) {

        list.add(s);

        System.out.print(s+ "|");

    }

    return list;

}

Can someone please explain why the pipe character needs to be escaped for the split() method?

Answer 1

String.split expects a regular expression argument. An unescaped | is parsed as a regex meaning "empty string or empty string," which isn't what you mean.