How do we remove the first line of a string in java? Each line is delimited by a \n or \r character.

Example: "Line0\n-[Stuff] Some stuff\n-[OtherStuff] Some other stuff"

Should be: "-[Stuff] Some stuff\n-[OtherStuff] Some other stuff"

CodePudding user response：

Using Streams (Java 11 required)

This compact solution is possible on Java 11 and higher:

String input = "Line0\r-[Stuff] Some stuff\n-[OtherStuff] Some other stuff";
String result = input.lines().skip(1).collect(Collectors.joining("\n"));

Note that the line separators of the remaining lines will be normalized to what you specify in the collector (e.g. if the input contains \r the output contains \n), which might be desirable for further processing.

This implementation is not the best concerning performance, because all lines are deconstructed and the relevant ones are joined again. If your method is called often, consider using the following solution, which should be faster.

Using Regular Expressions and substring()

You could also find the first newline occurrence using a regular expression and then extract the remaining substring:

public class LineExtractor
{
    /**
     * This regular expression matches {@code \n}, {@code \r} and {@code \r\n}.
     * <p>
     * On Java 8 and higher, {@code "\\R"} can be used instead.
     */
    private static final Pattern NEWLINE_CHARACTERS = Pattern.compile("\\r?\\n|\\r"); 
    
    public static String findContentAfterFirstLine(String input)
    {
        Matcher matcher = NEWLINE_CHARACTERS.matcher(input);
        if (matcher.find())
        {
            return input.substring(matcher.end());
        }
        
        // we get here if the input does not contain any newline characters
        // you might also choose to throw an exception instead of returning null
        return null;
    }
    
    public static void main(String[] args)
    {
        String input = "Line0\r-[Stuff] Some stuff\n-[OtherStuff] Some other stuff";
        String result = findContentAfterFirstLine(input);
        System.out.println(result); // prints -[Stuff] Some stuff\n-[OtherStuff] Some other stuff
    }
}

Note that it's a good idea to compile the regular expression only once (like in my example above, e.g. using a static member), and not every time you call the extraction method.

CodePudding user response：

I know it's tagged as "regex" but in case you want to implement a method to do that, you could use something like this:

public class RemoveFirstLine {
    public static void main(String[] args) {
        String input = "Line0\n-[Stuff] Some stuff\n-[OtherStuff] Some other stuff";
        System.out.println(removeFirstLine(input));
    }

    private static String removeFirstLine(String input) {
        char[] characters = input.toCharArray();
        int startingPoint = 0;
        int index = 0;
        for (char ch : characters) {
            if (ch == '\n' || ch == '\r') {
                startingPoint = index   1;
                break;
            }
            index  ;
        }
        if (startingPoint != 0 ) {
            char[] finalChars = Arrays.copyOfRange(characters, startingPoint, characters.length);
            return new String(finalChars);
        } else {
            return new String(characters);
        }
    }
}