Best way to replace two first characters of String from every line JAVA

I have a text file with about 3 million lines and I need to replace the first two characters of every line with "". My current code is 

String[] lines = content.split("\n");
        content = "";
        for(int i = 0;i<lines.length;i++){
            System.out.println(i);
            lines[i].substring(2);
            content = content + lines[i];
        }

It takes it about 3-4 days to finish. Is there a faster way of doing this?

My entire code:

 try {
        String content = readFile("text.txt", StandardCharsets.ISO_8859_1);
        content = content.replaceAll("\\d","");
        content = content.replaceAll("\\.","");
        String[] lines = content.split("\n");
        content = "";
        for(int i = 0;i<lines.length;i++){
            System.out.println(i);
            lines[i].substring(2);
            content = content + lines[i];
        }
         PrintWriter out = new PrintWriter("texty text.txt");
        out.println(content);
    } catch (IOException e) {
        e.printStackTrace();
    }
Jon Skeet
people
quotationmark

Is there a faster way of doing this?

Yes - don't perform repeated string concatenation. That's the part that's killing your performance. Use a StringBuilder instead.

It's also not even doing what you want it to - you're not using the result of calling substring.

I suspect you want something like this:

String[] lines = content.split("\n");
StringBuilder builder = new StringBuilder();
for (String line : lines) {
    builder.append(line.substring(2));
    // I suspect you want this, otherwise you're losing line breaks.
    builder.append("\n");
}
String result = builder.toString();

Additionally, you should consider reading the file line by line instead of reading the whole thing and then splitting it. For example:

StringBuilder builder = new StringBuilder();
try (BufferedReader reader = ...) {
    String line;
    while ((line = reader.readLine()) != null) {
        builder.append(line.substring(2));
        builder.append("\n");
    }
}
String result = builder.toString();

And unless you really need the whole thing in memory at any one time at all, write the lines as you process them:

try (BufferedReader reader = ...,
     BufferedWriter writer = ...) {
    String line;
    while ((line = reader.readLine()) != null) {
        // Perform any other manipulations here...
        writer.write(line.substring(2));
        writer.write("\n");
    }
}

people

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