Sorting a Java String Array with a pattern

I am currently reading and writing to a text file and I cant figure out a way to sort. I thought I would be able to sort by pattern. I would like to sort a java string array by the pattern (0-9, A-Z, a-z). Basically I would like to ignore non-alphanumeric characters, sort with numbers preceding letters, and capital letters preceding lowercase letters (i.e., 0-9, A-Z, a-z). I would like to remove lines that only have non-alphanumeric characters.

File f1 = new File(fp);
FileReader fr = new FileReader(f1);
BufferedReader br = new BufferedReader(fr);
List<String> lines = new ArrayList<String>();
String line;
while ((line = br.readLine()) != null) {
    count++;
    // SORT GOES HERE

    if (line.contains(sx)) {
        line = line.replace(line, "");
    }

    if (yint > 0 && !line.isBlank()) {
        line = line.substring(yint);
    }

    if(!line.isBlank()){
        line = line.replace(line, count + " " + line + "\n");
        lines.add(line);
    } else {
        lines.add(line);
    }
}
fr.close();
br.close();

FileWriter fw = new FileWriter(f1);
BufferedWriter out = new BufferedWriter(fw);
for(String s : lines)
    out.write(s);
out.flush();
out.close();

I would likely use something like Collections.sort() at the end and a simple check in the loop:

    File f1 = new File(fp);
    FileReader fr = new FileReader(f1);
    BufferedReader br = new BufferedReader(fr);
    List<String> lines = new ArrayList<String>();
    String line;
    while ((line = br.readLine()) != null) {
        count++;

        if (!line.matches("[a-zA-Z0-9]+")) {
            continue;
        }

        if (line.contains(sx)) {
            line = line.replace(line, "");
        }

        if (yint > 0 && !line.isBlank()) {
            line = line.substring(yint);
        }

        if(!line.isBlank()){
            line = line.replace(line, count + " " + line + "\n");
            lines.add(line);
        } else {
            lines.add(line);
        }
    }
    fr.close();
    br.close();

    Collections.sort(lines, (a, b) -> {
        String aNum = a.replaceAll("[^a-zA-Z0-9]", "");
        String bNum = b.replaceAll("[^a-zA-Z0-9]", "");
        return a.compareTo(b);
    });

    FileWriter fw = new FileWriter(f1);
    BufferedWriter out = new BufferedWriter(fw);
    for(String s : lines)
        out.write(s);
    out.flush();
    out.close();

EDIT: You can certainly make this work faster/better by quick-checking perhaps in the sort, etc - but generally this is the idea I think

You can't sort the file while you are reading it, in your case it needs to be done before:

// Sort the file
Path initialFile = Paths.get("myFile.txt");
List<String> sortedLines = Files.lines(initialFile)
		.sorted()
		.collect(Collectors.toList());

// Process the sorted lines
List<String> lines = new ArrayList<String>();
int count=0;
for(String line : sortedLines) {
	System.out.println("l: "+line);
	count++;

	if (line.contains(sx)) {
		line = line.replace(line, "");
	}

	if (yint > 0 && !line.isEmpty()) {
		line = line.substring(yint);
	}

	if (!line.isEmpty()) {
		System.out.println("line:"+line);
		line = line.replace(line, count + " " + line + "\n");
		System.out.println("new line:"+line);
		lines.add(line);
	} else {
		System.out.println("add:"+line);
		lines.add(line);
	}
}
// Write output file
File f1 = new File("myFile.txt");
try(BufferedWriter out = new BufferedWriter( new FileWriter(f1))){
	for (String s : lines)
		out.write(s);
}

Try this.

static void sortByAlphaNumeric(String inFile, String outFile) throws IOException {
    List<String> lines = Files.readAllLines(Paths.get(inFile)).stream()
        .map(line -> new Object() {
            String sortKey = line.replaceAll("[^0-9A-Za-z]", "");
            String originalLine = line;
        })
        .filter(obj -> !obj.sortKey.equals(""))
        .sorted(Comparator.comparing(obj -> obj.sortKey))
        .map(obj -> obj.originalLine)
        .collect(Collectors.toList());
    Files.write(Paths.get(outFile), lines);
}