How to zip two Java Lists

Question

I have 2 Lists:

List<String> subjectArr = Arrays.asList<String>("aa", "bb", "cc"); List<Long> numArr = Arrays.asList<Long>(2L, 6L, 4L); 

How do I create new List and zip two Lists into it?

List<?> subjectNumArr = zip(subjectArr, numArr); // subjectNumArr == [{'aa',2},{'bb',6},{'cc',4}] 

Answer 1

Here's Java-8 solution using the Pair class (like in @ZhekaKozlov answer):

public static <A, B> List<Pair<A, B>> zipJava8(List<A> as, List<B> bs) {     return IntStream.range(0, Math.min(as.size(), bs.size()))             .mapToObj(i -> new Pair<>(as.get(i), bs.get(i)))             .collect(Collectors.toList()); } 

In Java 9 onwards you can use Map.entry():

    public static <A, B> List<Map.Entry<A, B>> zipJava8(List<A> as, List<B> bs) {         return IntStream.range(0, Math.min(as.size(), bs.size()))                 .mapToObj(i -> Map.entry(as.get(i), bs.get(i)))                 .collect(Collectors.toList());     } 

Answer 2

As per related question, you can use Guava (>= 21.0) to do this:

List<String> subjectArr = Arrays.asList("aa", "bb", "cc"); List<Long> numArr = Arrays.asList(2L, 6L, 4L); List<Pair> pairs = Streams.zip(subjectArr.stream(), numArr.stream(), Pair::new)         .collect(Collectors.toList()); 

Note that the guava method is annotated as @Beta, though what that means in practice is up to interpretation, the method has not changed since version 21.0.