How to combine two lists using the Java stream API

Given the following lists of strings:

partnersName = ["partner1","partner2"];

totalDates = ["2022-05-18","2022-05-19"];

Here is the following code which gives output that I want:

for (int i = 0; i < partnersName.size(); i++) {
    if (totalDates.isEmpty()) {
        totalDates.add(partnersName.get(i));
    } else {
        for (int j = 0; j < totalDates.size(); j++) {
            totalDates.set(j, partnersName.get(i) +"/" +totalDates.get(j));
        }
    }
}

Desired output:

output = ["partner1/2022-05-18","partner2/2022-05-18","partner1/2022-05-19","partner2/2022-05-19"];

I want to reduce the line of code using the Java stream API. Could anyone help to get stream API code?

Here is one way.

List<String> partnerName = List.of("partner1","partner2");
List<String> totalDates = List.of("2022-05-18","2022-05-19");

List<String> result = partnerName.stream()
        .flatMap(name -> totalDates.stream()
                .map(date->String.join("/", name, date)))
        .toList();
    
System.out.println(result);

prints

[partner1/2022-05-18, partner1/2022-05-19, partner2/2022-05-18, partner2/2022-05
-19]

• The above uses nested streams to process each List.
• String.join - takes a delimiter and a variable number of arguments and concatenates them, separated by the delimiter.
• flatMap flattens the nested streams into one for conversion to a list.