Why Should I Escape the Pipe Character in Java\'s String.split Method?

Escaping Pipe Delimiters in String.split

When using the split method on a string, it's important to understand the significance of escaping certain characters. In particular, the pipe character (|) acts as a special delimiter, and its presence without escaping can lead to unexpected results.

Why Escape the Pipe?

The split method expects a regular expression argument, where each character represents a specific pattern matching rule. When an unescaped pipe is used, it is interpreted as a logical OR operator within the regex. This means it represents a pattern that matches either an empty string or another empty string, which is not the intended behavior.

Example

Consider the following snippet of code, which tries to parse a line with pipe-delimited values:

private ArrayList<String> parseLine(String line) {
    ArrayList<String> list = new ArrayList<String>();
    String[] list_str = line.split("|");
    for(String s:list_str) {
        list.add(s);
        System.out.print(s+ "|");
    }
    return list;
}

Without escaping the pipe, this code will incorrectly match every character in the string as a delimiter, resulting in an empty array.

Solution: Escape the Pipe

To ensure that the pipe is recognized as a literal delimiter, it must be escaped using the backslash character. This indicates to the split method that the pipe should be treated as a character rather than a regex operator:

private ArrayList<String> parseLine(String line) {
    ArrayList<String> list = new ArrayList<String>();
    String[] list_str = line.split("\|");
    for(String s:list_str) {
        list.add(s);
        System.out.print(s+ "|");
    }
    return list;
}

By escaping the pipe using "|", the split method now correctly separates the values in the line.

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