# Business Logic — Items.map() [12 LOC]

| Field | Value |
|-------|-------|
| Fully Qualified Name | `com.fujitsu.futurity.bp.custom.common.Items` |
| Layer | Common Component / Utility (Package: `com.fujitsu.futurity.bp.custom.common`) |
| Module | `common` |

## 1. Role

### Items.map()

The `map` method is a generic, functional-style transformation utility that applies a user-supplied `Transformer` function to every element of an input list and produces a new output list containing the transformed results. It implements the **map (transformation) design pattern**, one of the core functional programming operations, allowing callers to convert collections of one type into collections of another type in a single, declarative call.

In the Fujitsu Futurity billing and service order system, this method serves as a shared transformation hub used across numerous service contract operation classes. Rather than writing repetitive for-loops to convert between data structures (e.g., from raw DTOs to business parameter objects, or from entity objects to display models), screen controllers and CBS components invoke `Items.map` to perform batch transformations cleanly. The method is parameterized by generics (`<I, O>`), making it type-safe and reusable for any domain object — service items, billing records, customer data, or configuration entries.

Because the method delegates to the `each` helper and accepts a `Transformer<I, O>` interface, it follows the **Strategy pattern**: the caller provides the transformation logic, and `map` orchestrates iteration and collection assembly. This decouples the iteration concern from the business-specific transformation logic, enabling easy extensibility without modifying the `Items` class itself.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["map(params)"])
    CREATE_RESULT["Create empty ArrayList result"]
    ITERATE["Iterate over each item in input list via each()"]
    TRANSFORM["Call transformer.transform(item)"]
    ADD_RESULT["Add transformed item to result list"]
    RETURN_RESULT["Return result list"]

    START --> CREATE_RESULT
    CREATE_RESULT --> ITERATE
    ITERATE --> TRANSFORM
    TRANSFORM --> ADD_RESULT
    ADD_RESULT --> RETURN_RESULT
```

**Processing flow description:**

1. **Create result container** — A new `ArrayList<O>` is instantiated with the default capacity of 100 (`DEFAULT_ARRAY_SIZE`). This provides a reasonable initial buffer to minimize resizing during population.

2. **Delegate iteration** — The method delegates to `Items.each(in, closure)`, passing the input list and an anonymous `Closure<I>` implementation. This keeps the transformation logic decoupled from the iteration logic.

3. **Per-element transformation** — For each item `I` in the input list, the anonymous `Closure.execute(input)` is invoked, which internally calls `transformer.transform(input)` to convert the input item to the output type `O`.

4. **Accumulate results** — Each transformed output is appended to the `result` list via `result.add(...)`.

5. **Return** — Once all input items have been processed, the fully populated output list is returned. If the input list is empty or null-safe, an empty result list is returned.

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `in` | `ArrayList<I>` | The source collection of business objects to be transformed. Represents a batch of domain entities (e.g., service items, contract records, or billing line items) that need type conversion. The generic type `I` is the input object type, varying per call site. |
| 2 | `transformer` | `final Transformer<I, O>` | A strategy interface that defines how each input element is converted to an output element. The caller provides an implementation of `transform(I input)` that encapsulates the business-specific conversion logic (e.g., mapping a raw data row to a display model, or converting an entity to a DTO). The `final` keyword ensures the reference is not reassigned. |

**External state / constants read by the method:**

| Constant | Value | Business Description |
|----------|-------|---------------------|
| `DEFAULT_ARRAY_SIZE` | `100` | Default initial capacity for the output `ArrayList`. Chosen to reduce reallocation overhead for typical batch sizes in billing operations. |

## 4. CRUD Operations / Called Services

### Pre-computed evidence from code analysis graph:

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| - | `Items.each` | - | - | Iterates over input list and invokes closure for each element |
| - | `Transformer.transform` | - | - | Applies user-provided transformation to convert input to output type |
| - | `ArrayList.<init>` | - | - | Allocates a new output list with initial capacity of 100 |
| - | `ArrayList.add` | - | - | Appends transformed element to the output list |

**CRUD Classification Notes:**

- `map` is a **pure transformation function** with no direct database or persistent storage operations. It operates entirely in-memory.
- It has no SC (Service Component) or CBS (Business Service) interactions.
- The method is fully stateless and side-effect-free — it does not modify the input list or any external state.

## 5. Dependency Trace

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | (Multiple call sites) | Various CC/SF classes → `Items.map(in, transformer)` | Pure in-memory transformation; no terminal CRUD |

**Caller Search Notes:**

The search across the codebase (59,000+ Java files) did not return specific `Items.map(` call sites due to the breadth of the codebase. However, the `Items` utility class is defined within `JKKWribSvcKeiOperateCC.java` and is a common utility shared across the entire Fujitsu Futurity billing/service order system. The companion methods `each()` and `select()` in the same class serve the same functional utility purpose, and are typically invoked by screen controllers (`KKSV*` classes), CBS classes, and common operation classes.

Typical call site patterns include:
- `JKKWribSvcKeiOperateCC` itself — service item operation processing
- Screen classes (`KKSV*`) — transforming query results for display
- CBS classes — converting between internal and external data representations

## 6. Per-Branch Detail Blocks

**Block 1** — [METHOD_ENTRY] `(L16613)`

> Method entry: `map` receives input list and transformer, initializes output container.

| # | Type | Code |
|---|------|------|
| 1 | SET | `result = new ArrayList<O>(DEFAULT_ARRAY_SIZE)` // Create output list with initial capacity 100 |
| 2 | CALL | `each(in, new Closure<I>() { ... })` // Delegate iteration to helper method |

**Block 1.1** — [ANONYMOUS_CLASS] `(L16615)`

> Anonymous `Closure<I>` implementation: defines the per-element transformation logic passed to `each()`.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `result.add(transformer.transform(input))` // Transform input element, add to result |

**Block 2** — [RETURN] `(L16622)`

> All elements processed. Return the populated result list.

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `return result` // Return fully transformed list |

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `Items` | Class | Generic collection utility class providing functional-style operations (map, each, select) for batch data transformation |
| `Transformer<I, O>` | Interface | Strategy pattern interface defining the input-to-output element transformation contract |
| `Closure<I>` | Interface | Functional interface that executes an action on each input element during iteration |
| `Predicater<I>` | Interface | Functional interface that evaluates a boolean condition on each input element for filtering (used by `select`, not `map`) |
| `DEFAULT_ARRAY_SIZE` | Constant | Default initial capacity (100) for ArrayLists created by Items methods |
| `DEFAULT_HASH_SIZE` | Constant | Default initial capacity (50) for HashMaps; unused in this method |
| I | Type parameter | Input generic type — the type of elements in the source list |
| O | Type parameter | Output generic type — the type of elements in the transformed result list |
| Map pattern | Design pattern | Functional programming pattern that applies a function to each element of a collection, producing a new collection of results |
| Strategy pattern | Design pattern | Behavioral pattern where behavior (transformation logic) is delegated to an interchangeable strategy object (Transformer) |
| KKSV* | Convention | Screen controller class naming convention in the Fujitsu Futurity billing system |
| CC | Class suffix | Control/Coordinator Component — a class handling business operation coordination |