Is there an easy way to concatenate several lines of text into a string without constantly appending a newline?

You can use a StringWriter wrapped in a PrintWriter:

StringWriter stringWriter = new StringWriter();
PrintWriter writer = new PrintWriter(stringWriter, true);
writer.println("line1");
writer.println("line2");
writer.println("line3");
useString(stringWriter.toString());

AFAIK there's no library class that allows you to do so.

The following does the work though:

class DesiredStringThinger {
  StringBuilder text = new StringBuilder();

  public void append(String s) { text.append(s).append("\n"); }

  @Override
  public String toString() { return text.toString(); }
}

public String createString () {
   StringBuilder sb = new StringBuilder ();
   String txt = appendLine("firstline", sb).appendLine("2ndLine", sb).toString();
}

private StringBuilder appendLine (String line, StringBuilder sb) {
   String lsp = System.getProperty("line.separator");
   return sb.append (line).append (lsp);
}