How Can I Convert a List to a Map in Java 8 Using Streams?

Java 8: Convert List to Map

In Java 8 and above, you can easily convert a list of objects into a map using the powerful stream API and lambdas, without relying on third-party libraries. Let's modify the Java 7 example:

private Map<String, Choice> nameMap(List<Choice> choices) {
    Map<String, Choice> hashMap = choices.stream()
        .collect(Collectors.toMap(Choice::getName, Function.identity()));
    return hashMap;
}

Here's what's happening in this code:

1. The stream() method creates a stream of Choice objects from the original List.
2. The collect() method terminates the stream and collects the elements into a Map.

3. The Collectors.toMap() collector is used to create the map. It takes two arguments:

   • The first argument is a function that maps each element in the stream to the key of the map. Here, Choice::getName is used to map each choice to its name.
   • The second argument is a function that maps each element in the stream to the value of the map. In this case, Function.identity() is used to keep the original choice as the value.
4. The resulting Map is stored in the hashMap variable and returned.

This approach leverages Java 8 streams to write succinct and efficient code for converting lists into maps.

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