I have a method like this:

public String mostExpensiveItems() {
        List<Entry> myList = getList();
        List<Double> expensive = myList.stream()
                .map(Entry::getAmount)
                .sorted(Comparator.reverseOrder())
                .limit(3)
                .toList();

        return "";
    }

This method needs to return the product IDs of the 3 most expensive items as a string like this: "item1, item2, item3". I should be able to use only streams and I got stuck here. I should be able to sort the items by value then get the product IDs, but I can't seem to make it work.

Edit:

Product ID is located in the Entry class

public class Entry {

    private String productId;
    private LocalDate date;
    private String state;
    private String category;
    private Double amount;

    public Entry(LocalDate orderDate, String state, String productId, String category, Double sales) {
        this.date = orderDate;
        this.productId = productId;
        this.state = state;
        this.category = category;
        this.amount = sales;
    }

    public String getProductId() {
        return productId;
    }

CodePudding user response：

Assuming product ID is inside Entry, it can be something like this.

public String mostExpensiveItems() {
    List<Entry> myList = getList();
    List<String> expensive = myList.stream()
            .sorted(Comparator.comparing(Entry::getAmount).reversed())
            .limit(3)
            .map(Entry::getProductID)
            .toList();

    return "";
}

NB: I didn't test this out yet, but this should be able to convey the idea.