Is it possible to extract the key set from a LinkedHashMap, apply a sorting algorithm on it and put it back into the map?

I have .csv file that has a list of grocery items that has their UPC code and the product name. I already wrote some code to put the product's code and its name into a map and they are working fine (code shown below). Without using a TreeMap or anything related directly to using the Map interface, how do I extract the key set of the map into a list and apply a sorting algorithm on it (like quick sort, for example) and have an output of those sorted keys with their assigned value? (I can write the sorting algorithm by myself so it's not a concern). The keys and values are unique.

I can change the method to use an array list instead of a map and directly apply the sorting algorithm on in. I also know there are various great ways to do this sorting revolving around using the Map interface, but this is just for the sake of practicing and I'm curious to know how do I implement something like that.

My item list look like this (I use the second data row 'upc14' as key and the final data row 'name' as value):

grp_id,upc14,upc12,brand,name
1,00035200264013,035200264013,Riceland,Riceland American Jazmine Rice
2,00011111065925,011111065925,Caress,Caress Velvet Bliss Ultra Silkening Beauty Bar - 6 Ct
3,00023923330139,023923330139,Earth's Best,Earth's Best Organic Fruit Yogurt Smoothie Mixed Berry
4,00208528800007,208528800007,Boar's Head,Boar's Head Sliced White American Cheese - 120 Ct
5,00759283100036,759283100036,Back To Nature,Back To Nature Gluten Free White Cheddar Rice Thin Crackers
6,00074170388732,074170388732,Sally Hansen,Sally Hansen Nail Color Magnetic 903 Silver Elements
7,00070177154004,070177154004,Twinings Of London,Twinings Of London Classics Lady Grey Tea - 20 Ct
8,00051600080015,051600080015,Lea & Perrins,Lea & Perrins Marinade In-a-bag Cracked Peppercorn
9,00019600923015,019600923015,Van De Kamp's,Van De Kamp's Fillets Beer Battered - 10 Ct
10,00688267141676,688267141676,Ahold,Ahold Cocoa Almonds

public class ReadFile {
// File reading stuffs
private static Map<Long,String> readFromCSV() {
Map<Long,String> map = new LinkedHashMap<>();
try {
BufferedReader reader = new BufferedReader(new FileReader("Grocery_UPC_Database.csv"));
reader.readLine();
String line = reader.readLine();
while (line != null) {
String[] attributes = line.split(",");
for(int i = 1; i < attributes.length; i++) {
map.put(Long.parseLong(attributes[1]), attributes[4]);
}
line = reader.readLine();
}
reader.close();
} catch (IOException e) {
e.printStackTrace();
}
return map;
}
private static void createFile(Map<Long,String> map) {
PrintWriter out = null;
try {
out = new PrintWriter("output.txt");
} catch (FileNotFoundException e) {
e.printStackTrace();
}
for (Map.Entry<Long,String> entry : map.entrySet()) {
assert out != null;
out.println(entry.getValue());
}
assert out != null;
out.close();
}
public static void main(String[] args) {
Map<Long,String> map = readFromCSV();
createFile(map);
}
}

> how do I extract the key set of the map ...

Call keySet().

> ... into a list ...

Copy the keys into a List using the ArrayList constructor made for the purpose:

List<Long> keyList = new ArrayList<>(map.keySet());

> ... and apply a sorting algorithm on it (like quick sort, for example) ...

Call sort() (Java 8+) or Collections.sort(), with a Comparator that implements the desired ordering, e.g.

keyList.sort((a, b) -> Long.compare(b, a)/*sort descending*/);

> ... and have an output of those sorted keys with their assigned value?

Iterate the list and print the values from the map, e.g.

for (Long key : keyList) {
System.out.println(key + " = " + map.get(key));
}

If you are using Java8, you can use streams to sort using compareByKey().

Map sortedMap = map.entrySet().stream().sorted(comparingByKey())
.collect(toMap(e -> e.getKey(), e -> e.getValue(), (e1, e2) -> e2), LinkedHashMap::new));