convert map to list<string> - as “key-value” to each list entry

问题

I want to convert Map<Integer, String> to List<String> with each map entry - to 1 entry in the list as "key - value"

I searched and I only found to map values only to List.

Map<Integer, String> map = new HashMap<>();
    map.put(10, "apple");
    map.put(20, "orange");
    map.put(30, "banana");
    map.put(40, "watermelon");
    map.put(50, "dragonfruit");

I want this to be mapped to list as

 "10-apple" 
 "20-orange"

and so on.

this can be done easily if I used foreach .. but I want to know if it is feasible to get it through streams

回答1:

    List<String> list = map.entrySet()
                            .stream()
                            .map(entry -> entry.getKey() + "-" + entry.getValue())
                            .sorted()
                            .collect(Collectors.toList());

回答2:

Just a slightly different variant to the other answers. if the insertion/iteration order is important then I'd rather use a LinkedHashMap in the first place as opposed to using a HashMap then sorting it which is actually not always guaranteed to work.

Example:

Map<Integer, String> map = new LinkedHashMap<>();
...
...
...

then stream over the entrySet and collect to a list implementation:

List<String> list = map.entrySet()
                        .stream()
                        .map(e -> e.getKey() + "-" + e.getValue())
                        .collect(Collectors.toList());

回答3:

Here is one variant using .map to move from list to map

List<String> list = map.entrySet()
                       .stream()
                       .map(x -> String.format("%d-%s", x.getKey().intValue(), x.getValue()))
                       .sorted().collect(Collectors.toList());

来源：https://stackoverflow.com/questions/51341620/convert-map-to-liststring-as-key-value-to-each-list-entry