how to initialize a hashmap in java code example

Example 1: new hashmap java

Map<String, String> myMap = new HashMap<String, String>() {{
        put("a", "b");
        put("c", "d");
    }};

Example 2: java 11 initialize map

Map<String, String> emptyMap = Map.of();
Map<String, String> singletonMap = Map.of("key1", "value");
Map<String, String> map = Map.of("key1","value1", "key2", "value2");

Example 3: java initialize map with values in one line

Map<String, Integer> map = Stream.of(
  new AbstractMap.SimpleEntry<>("idea", 1), 
  new AbstractMap.SimpleEntry<>("mobile", 2))
  .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));