multiple lists into a map - list

Question

I had a question regarding my code below. I'm reading a file containing lots of data of which some stuff is irrelevant. The data is written out on one line, so I cannot use nextLine or something.
For each vertex, I save the relevant information into dataperpoint. When I go to the next vertex, I want to clear the list to fill it with new relevant information.
The issue that I have is that each time I clear dataperpoint, all values in Map get cleared. When I then try to fill it, all previous positions in the Map get the same values.
How can I do this and make sure that each vertex will get his own list?
Looking forward to your suggestions!
public static Map<Integer, List<Double>> readData(File f) // throws IO exception?
{
// Create Map to store the vertex and list with relevant information in
List<Double> dataperpoint = new ArrayList<Double>();
Map<Integer, List<Double>> data = new HashMap<>();
// Open the scanner
try (Scanner in = new Scanner(f))
{
// To make sure the correct localization is used
in.useLocale(Locale.US);
// The first six integers contain irrelevant information
for (int step = 1; step <= 6; step++)
{
in.nextInt();
}
// Do the information for vertex 0 separately, since it has one data point less
int vertex = in.nextInt();
for (int doubleinfo = 1; doubleinfo <= 4; doubleinfo++) // six relevant variables
{
dataperpoint.add(in.nextDouble());
}
// irrelevant information
for (int irrelevantinfo = 1; irrelevantinfo <= 2; irrelevantinfo++)
{
in.nextInt();
}
// Opening and Closing of time window
dataperpoint.add((double) in.nextInt());
dataperpoint.add((double) in.nextInt());
data.put(vertex, dataperpoint);
while (in.hasNext()) // think of different statement later
{
dataperpoint = new ArrayList<Double>();
vertex = in.nextInt();
for (int doubleinfo = 1; doubleinfo <= 4; doubleinfo++) // six relevant variables
{
dataperpoint.add(in.nextDouble());
}
// irrelevant information
for (int irrelevantinfo = 1; irrelevantinfo <= 3; irrelevantinfo++)
{
in.nextInt();
}
// Opening and Closing of time window
dataperpoint.add((double) in.nextInt());
dataperpoint.add((double) in.nextInt());
data.put(vertex, dataperpoint);
}
in.close();
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}

Answer 1

Use LinkedHashMap<> instead of HashMap<> it should solve your problem. Read this Difference between HashMap, LinkedHashMap and TreeMap