Trying to reverse my stream in ascending order – Java 8

This idea behind this code is that it reads the data from three .csv files w/ keys organized by year, and retrieves the sum of the data by year, as well as the minimum and maximum number for each year.

The problem is, when print it returns the yearly results in descending order.

I need help figuring out a way to reverse the stream, so that yearly data from each file is in ascending order.

public class SalesGenerator {
    
    //This class will print out the Maximum and minimum Sales data from the .getSales() in TeslaImport.
    public static void teslaReport(
        Set<Entry<String, List<TeslaImport>>> entrySet, 
        List<TeslaImport> teslaModel, String modelName) 
    throws IOException {        
        //This comparator will sort the sales array values.
        Comparator<TeslaImport> comparativeOperator = Comparator.comparing(tesla -> tesla.getSales());

        entrySet.stream().forEach(entry -> System.out.println(
            "Month: " + entry.getKey() + " -> " 
            + entry.getValue().stream()
                .mapToInt(tesla -> tesla.getSales().intValue())
                .sum()
        ));
        
        TeslaImport maximumSales = teslaModel.stream()
            .max(comparativeOperator)
            .orElseThrow(NoSuchElementException::new);
        TeslaImport minimumSales = teslaModel.stream()
            .min(comparativeOperator)
            .orElseThrow(NoSuchElementException::new);
            
        //Print out the maximum and minimum results from TeslaReport.
        System.out.println(modelName + " Yearly Sales Report");
        System.out.println("The BEST month for " + modelName + " was: " + maximumSales.getDate());
        System.out.println("The WORST month for " + modelName + " was: " + minimumSales.getDate());                                                                                 
    } 
    
    public static void main(String[] args) throws IOException {
        
        /* To produce the sales values from TeslaData, we need to instantiate the TeslaData variable to import
        all the EntrySet models */
        TeslaData analysedData = new TeslaData();
        
        /*The FileReader from our FileGenerator class needs to be instantiated to model3. We can use to when
        when reporting our data in TeslaReport */
        List<TeslaImport> model3 = FileGenerator.teslaFileRead("model3.csv");
        Set<Entry<String, List<TeslaImport>>> entrySetModel3 = analysedData.entryByYear(model3);
        teslaReport(entrySetModel3, model3, "Model 3");
        
        /*The FileReader from our FileGenerator class needs to be instantiated to modelS. We can use to when
        when reporting our data in TeslaReport */
        List<TeslaImport> modelS = FileGenerator.teslaFileRead("modelS.csv");
        Set<Entry<String, List<TeslaImport>>> entrySetModelS = analysedData.entryByYear(modelS);
        teslaReport(entrySetModelS, modelS, "Model S");
        
        /*The FileReader from our FileGenerator class needs to be instantiated to modelX. We can use to when
        when reporting our data in TeslaReport */
        List<TeslaImport> modelX = FileGenerator.teslaFileRead("modelX.csv");   
        Set<Entry<String, List<TeslaImport>>> entrySetModelX = analysedData.entryByYear(modelX);        
        teslaReport(entrySetModelX, modelX, "Model X");
    }
}

Note: TeslaImport is the class where I placed my JavaBean’s (get/set, toString, date, and sales)

Answer

As the report data are printed for the entry set retrieved from the method entryByYear in TeslaModel class, it is very likely that this method returns the entry set for a tree map sorted in the descending order. Thus, to change the order, the stream should be re-sorted by key:

entrySet.stream()
    .sorted(Map.Entry.comparingByKey())
    .forEach(entry -> System.out.println(
            "Month: " + entry.getKey() + " -> " 
            + entry.getValue().stream()
                .mapToInt(tesla -> tesla.getSales().intValue())
                .sum()
        ));

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Answer