The given code defines a Java class and initializes a...

The given code defines a Java class and initializes a static Map named vMap that likely creates mappings between string representations of an enum (MyOrigEnum) and instances of the MyDerivedType class. Let’s break it down step by step to understand what it does:

private static final Map<String, MyDerivedType> vMap =
    Stream.of(MyOrigEnum.values())
          .collect(Collectors.toMap(
              e -> e.getValue() + " ",  // 1. Key: String value derived from `MyOrigEnum` values concatenated with a space.
              MyDerivedType::new,       // 2. Value: A new `MyDerivedType` instance is created for each enum value.
              (e1, e2) -> e2,           // 3. Merge function: If key collisions occur, keep the latest value.
              LinkedHashMap::new        // 4. Use a `LinkedHashMap` to maintain insertion order.
          ));

Detailed Explanation:

1. Enum Conversion to Stream (Stream.of(MyOrigEnum.values())):

   • MyOrigEnum.values() returns an array of all constants in the MyOrigEnum enum.
   • This array is converted to a Stream to allow functional processing.

2. Key Generation (e -> e.getValue() + " "):

   • The lambda function e -> e.getValue() + " " is used to generate keys for the map.
   • For each enum constant, its getValue() method is called (likely retrieving some string representation of the enum constant) and appending a space (" ").

3. Value Generation (MyDerivedType::new):

   • The method reference MyDerivedType::new is used to create new instances of the MyDerivedType class for each enum constant.
   • This assumes that MyDerivedType has a constructor that accepts a single parameter (possibly MyOrigEnum).

4. Handling Duplicate Keys ((e1, e2) -> e2):

   • If two enum constants produce the same key (which would happen if two getValue() results are the same, differing only by appended whitespace), the second value (e2) will overwrite the first (e1).

5. Map Implementation (LinkedHashMap::new):

   • A LinkedHashMap is used to store the resulting key-value pairs, which preserves the order in which elements are added to the map.

6. Static Final Field:

   • The resulting map (vMap) is stored in a static final field, meaning it is a constant and shared among all instances of MyDerivedType.

Simplified Summary:

• This code constructs a static LinkedHashMap called vMap.
• The keys in the map are strings created by appending a space to the enum's getValue() method.
• The values in the map are new MyDerivedType instances created for each enum constant.
• If there are any key collisions, the later value will overwrite the earlier one.
• The map preserves insertion order because LinkedHashMap is used.

Let me know if you'd like further clarification!