What is the method for initializing and assigning values in a map in Java?

2 years ago
William Carter
1 minute

In Java, there are various ways to initialize and assign values to a Map object. Here are some common methods:

  1. Initialize and assign values literally.
Map<String, Integer> map = new HashMap<>();
map.put("key1", 1);
map.put("key2", 2);
  1. Initializing and assigning values using the constructor of the implementing class of Map.
Map<String, Integer> map = new HashMap<>(Map.of("key1", 1, "key2", 2));

Alternatively:

Map<String, Integer> map = new HashMap<>(Map.ofEntries(
    Map.entry("key1", 1),
    Map.entry("key2", 2)
));
  1. add all items to the collection
Map<String, Integer> originalMap = new HashMap<>();
originalMap.put("key1", 1);
originalMap.put("key2", 2);

Map<String, Integer> newMap = new HashMap<>();
newMap.putAll(originalMap);
  1. Flow continuously in a particular direction.
Map<String, Integer> map = Stream.of(
    new AbstractMap.SimpleEntry<>("key1", 1),
    new AbstractMap.SimpleEntry<>("key2", 2)
).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

These are some common methods, so you can choose the appropriate initialization and assignment methods based on specific needs and usage scenarios.

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