# Business Logic — Items.select() [10 LOC]

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

## 1. Role

### Items.select()

`Items.select()` is a generic, reusable utility method that filters a list by applying a predicate — a functional interface called `Predicater<I>` — to each element. It follows a functional-stream pattern (akin to Java 8's `Stream.filter()`), enabling callers to express filtering logic inline via anonymous classes or lambda expressions. The method is purely functional in its effect: it reads every element from the input list without mutating it, evaluates each against the predicate, and produces a new list containing only the elements that satisfy the condition. This method plays the role of a shared data-processing primitive, called from multiple areas of the `JKKWribSvcKeiOperateCC` class to filter lists of service-contract line items (`CAANMsg` objects), maps of key-value pairs, and other generic collections. Its design pattern is that of a higher-order function — it accepts logic (`Predicater`) as a parameter — making it the backbone for declarative filtering throughout the service layer. In the larger system, it abstracts away boilerplate iteration so callers can focus on what constitutes a "match" rather than how to collect matches.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["select in, predicater"])
    INIT["result = new ArrayList(DEFAULT_ARRAY_SIZE=100)"]
    LOOP["For each item in in"]
    EVAL["predicater.evaluate(item)"]
    COND{evaluate returns true?}
    ADD["result.add(item)"]
    NEXT["Advance to next item"]
    FINISH["Return result"]

    START --> INIT
    INIT --> LOOP
    LOOP --> EVAL
    EVAL --> COND
    COND -- true --> ADD
    COND -- false --> NEXT
    ADD --> NEXT
    NEXT --> LOOP
```

**CRITICAL — Constant Resolution:**

| Constant | Value | Business Meaning |
|----------|-------|-----------------|
| `DEFAULT_ARRAY_SIZE` | `100` | Default initial capacity for the result `ArrayList` |

**Processing flow description:**
1. **Initialization**: A new `ArrayList` is created with an initial capacity of `DEFAULT_ARRAY_SIZE` (100). This avoids repeated resizing for typical mid-sized lists while avoiding excessive memory allocation for small lists.
2. **Iteration**: The method iterates over every element in the input `ArrayList` using an enhanced for-each loop.
3. **Predicate evaluation**: For each element, the `Predicater<I>.evaluate(item)` method is invoked. This is the only branching point — the predicate is implemented by the caller and encodes the business filtering rule.
4. **Conditional collection**: If `evaluate()` returns `true`, the item is appended to the result list. If it returns `false`, the item is silently skipped.
5. **Return**: After all elements have been processed, the filtered result list is returned. If no elements match, an empty list is returned.

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `in` | `ArrayList<I>` | The source collection of items to filter. In practice, this carries business entities such as service-contract line items (`CAANMsg`), key-value maps (`HashMap<String, String>`), or other domain objects that need to be narrowed down to a relevant subset. |
| 2 | `predicater` | `Predicater<I>` | A functional interface that encapsulates the filtering rule. Its `evaluate(I input)` method returns `true` if the item should be included in the result. The caller implements this interface inline (via anonymous class or lambda) to express domain-specific selection criteria — e.g., "select only active service types" or "select items matching a specific service code." |

| # | Field / External State | Type | Business Description |
|---|----------------------|------|---------------------|
| 1 | `DEFAULT_ARRAY_SIZE` (static final) | `int = 100` | The default initial capacity used for the output `ArrayList`. Tuned as a practical heuristic for typical result sizes in the application. |

## 4. CRUD Operations / Called Services

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

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| R | `Predicater.evaluate` | Predicater (functional interface) | - | Reads each input item through the predicate's `evaluate` method. This is a read-only operation that evaluates business rules to decide inclusion. |

**Classification notes:**
- This method itself performs no direct database or entity-level operations (no INSERT/UPDATE/DELETE).
- It is a **Read (R)** operation at the collection level: it reads all elements from the input list and reads from the predicate's `evaluate` method, producing a filtered read result.
- The predicate's `evaluate` implementation (provided by the caller) may internally perform further database reads or business logic — but those are opaque from the perspective of `select()` itself.

## 5. Dependency Trace

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

No screen/batch entry points found within 8 hops. Direct callers found: 15 methods.
Terminal operations from this method: `evaluate` [-], `evaluate` [-], `evaluate` [-], `evaluate` [-], `evaluate` [-]

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | CBS: `JKKWribSvcKeiOperateCC.filterWribSvcKeis()` | `filterWribSvcKeis()` → `Items.select()` | `evaluate [R]` (predicate on CAANMsg list) |
| 2 | CBS: `JKKWribSvcKeiOperateCC.generateKeisForCreate()` | `generateKeisForCreate()` → `Items.select()` | `evaluate [R]` (predicate on CAANMsg list) |
| 3 | CBS: `JKKWribSvcKeiOperateCC.resolveDchskmCds()` | `resolveDchskmCds()` → `Items.select()` | `evaluate [R]` (predicate on map entries) |
| 4 | CBS: `JKKWribSvcKeiOperateCC.resolveSvcKeiNos()` | `resolveSvcKeiNos()` → `Items.select()` | `evaluate [R]` (predicate on map entries) |

**Notes on dependency trace:**
- All callers reside within the same CBS class (`JKKWribSvcKeiOperateCC`), confirming that `Items.select()` serves as an internal utility for the discount-service-contract screen logic.
- The terminal operation is always `evaluate` — the predicate encapsulates the actual business filtering rule, which varies per caller (e.g., filtering by service type code, status code, or numeric range).
- No direct screen or batch entry points were found within 8 hops, indicating `JKKWribSvcKeiOperateCC` itself is called by a higher-level controller or action class.

## 6. Per-Branch Detail Blocks

### Block 1 — STATEMENT (result initialization) (L16633)

> Creates the output collection with a pre-defined initial capacity to avoid repeated ArrayList resizing.

| # | Type | Code |
|---|------|------|
| 1 | SET | `ArrayList<I> result = new ArrayList<I>(DEFAULT_ARRAY_SIZE)` // Initialize output list with capacity 100 [-> DEFAULT_ARRAY_SIZE=100] |

### Block 2 — FOR LOOP (item iteration) (L16634)

> Iterates over every element in the input collection using an enhanced for-each loop. No nesting beyond the inner if-block.

| # | Type | Code |
|---|------|------|
| 1 | SET | `I item : in` // Enhanced for-each over input list — type parameter `I` resolves to caller's concrete type (e.g., CAANMsg, HashMap) |

**Block 2.1** — IF (predicate evaluation) (L16635)

> For each item, applies the caller's filtering logic. This is the only decision point in the method.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `predicater.evaluate(item)` // Invoke caller-supplied predicate — returns true if item should be included [Predicater<I>.evaluate] |

**Block 2.1.1** — IF body (add matching item) (L16636)

> Appends items that pass the predicate to the result list.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `result.add(item)` // Add matching item to filtered result list |

**Block 2.1.2** — IF false branch (implicit)

> Items that fail the predicate are silently skipped. No explicit else block exists — execution falls through to the next iteration.

| # | Type | Code |
|---|------|------|
| 1 | SKIP | (no operation) // Item does not satisfy predicate — proceed to next iteration |

### Block 3 — RETURN (L16638)

> Returns the fully constructed filtered list. If the input was empty or no items matched, returns an empty list.

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `return result` // Return the filtered collection |

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `Predicater<I>` | Interface | Functional interface defining a `boolean evaluate(I input)` contract. Encapsulates a single-item filtering rule supplied by the caller. |
| `Transformer<I, O>` | Interface | Functional interface defining an `O transform(I input)` contract. Used by the companion `Items.map()` method for type-conversion mapping. |
| `Closure<I>` | Interface | Functional interface defining a `void execute(I input)` contract. Used by the companion `Items.each()` method for side-effect operations on each item. |
| `DEFAULT_ARRAY_SIZE` | Constant | Default initial capacity (100) for newly created `ArrayList` instances within the `Items` utility class. |
| `Items` | Class | A static utility class embedded within `JKKWribSvcKeiOperateCC.java`. Provides functional-collection operations (`select`, `map`, `each`, `exist`) for generic Java collections without requiring external libraries. |
| `CAANMsg` | Entity | Service-contract line item message object — carries details of a single service type and pricing entry within a customer's discount service contract. |
| JKKWribSvcKeiOperateCC | Class | Discount Service Contract Operations Control Class — handles all CRUD and validation operations for the discount service-contract screen in the K-Opticom customer backbone system. |
| eo | System | "e-Opticom" — the NTT communication service customer management backbone system in which this code runs. |
| K-Opticom | Business term | A Japanese broadband ISP brand operated by NTT; the domain context for this codebase (telecom service order and contract management). |