---

# (DD10) Business Logic — NumericFilter.isValid() [17 LOC]

| Field | Value |
|-------|-------|
| Fully Qualified Name | `com.github.blaxk3.ui.NumericFilter` |
| Layer | Utility |
| Module | `ui` (Package: `com.github.blaxk3.ui`) |

## 1. Role

### NumericFilter.isValid()

This method performs local input validation for numeric text before the value is accepted into the UI editing flow. Its business purpose is to protect numeric entry fields from invalid characters while still allowing the user to type an empty value during editing and to enter a single decimal point for fractional numbers.

The method implements a simple validation-and-routing pattern: it evaluates the current text buffer, allows the empty state as a valid intermediate condition, then scans each character to decide whether the input remains admissible. Digits are accepted, one decimal separator is accepted, and any other character causes immediate rejection. In other words, this method acts as a shared guard for numeric screen input rather than as a business transaction handler.

Within the larger system, `isValid()` is a low-level UI utility that supports incremental typing behavior in numeric fields. It does not create, read, update, or delete domain records; instead, it enforces presentation-layer data integrity so that downstream business logic receives only properly formatted numeric input.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["isValid(text)"])
    CHECK_EMPTY{"text.isEmpty()?"}
    RETURN_TRUE_EMPTY(["return true"])
    INIT_DECIMAL(["Set decimalCount = 0"])
    LOOP_CHECK{"i < text.length()?"}
    GET_CHAR(["Read ch = text.charAt(i)"])
    CHECK_DOT{"ch == '.' and decimalCount != 1?"}
    INCREMENT(["decimalCount++"])
    CHECK_DIGIT{"Character.isDigit(ch)?"}
    RETURN_FALSE(["return false"])
    RETURN_TRUE(["return true"])
    START --> CHECK_EMPTY
    CHECK_EMPTY -->|Yes| RETURN_TRUE_EMPTY
    CHECK_EMPTY -->|No| INIT_DECIMAL
    INIT_DECIMAL --> LOOP_CHECK
    LOOP_CHECK -->|Yes| GET_CHAR
    GET_CHAR --> CHECK_DOT
    CHECK_DOT -->|Yes| INCREMENT
    INCREMENT --> LOOP_CHECK
    CHECK_DOT -->|No| CHECK_DIGIT
    CHECK_DIGIT -->|Yes| LOOP_CHECK
    CHECK_DIGIT -->|No| RETURN_FALSE
    LOOP_CHECK -->|No| RETURN_TRUE
```

**CRITICAL — Constant Resolution:**
This method does not reference any named constants or external constant classes. The only literal controls are the empty-string check, the decimal point character `'.'`, and the counter comparison against `1`.

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `text` | `String` | Current editable value from a numeric input field. It can be empty during typing, can include digits, and can include at most one decimal point. If it contains any other character, the method rejects it immediately. |

Instance fields and external state read by the method: none. The method evaluates only its input parameter and local variables.

## 4. CRUD Operations / Called Services

This method does not invoke any business service, repository, DAO, or SC/CBS operation. It is a pure validation helper that returns a boolean result based on character-level inspection.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| - | `isValid` | - | - | Pure UI validation logic; no persistence or service interaction |

## 5. Dependency Trace

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

No screen/batch entry points found within 8 hops. Direct callers found: 2 methods.
Terminal operations from this method: -

Trace who calls this method and what this method ultimately calls.

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | `UI$NumericFilter.insertString(...)` | `UI$NumericFilter.insertString(...)` -> `NumericFilter.isValid(String text)` | - |
| 2 | `UI$NumericFilter.replace(...)` | `UI$NumericFilter.replace(...)` -> `NumericFilter.isValid(String text)` | - |

## 6. Per-Branch Detail Blocks

**Block 1** — **IF** `(text.isEmpty())` (L196)

> Allows an empty buffer as a valid intermediate numeric entry state.

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `return true;` |

**Block 2** — **SET / FOR** `(initialize and iterate through text characters)` (L199-L208)

> Scans the candidate value one character at a time to confirm that it remains numeric.

| # | Type | Code |
|---|------|------|
| 1 | SET | `byte decimalCount = 0;` |
| 2 | SET | `for (int i = 0; i < text.length(); i++)` |
| 3 | EXEC | `char ch = text.charAt(i);` |

**Block 2.1** — **IF** `(ch == '.' and decimalCount != 1)` (L201)

> Accepts the first decimal point only. A second decimal point is not counted as valid punctuation and will be rejected by the digit check branch.

| # | Type | Code |
|---|------|------|
| 1 | SET | `decimalCount++;` |

**Block 2.2** — **ELSE-IF** `(!Character.isDigit(ch))` (L203)

> Rejects any non-digit character that is not the allowed decimal separator.

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `return false;` |

**Block 3** — **RETURN** `(after loop completes)` (L209)

> Confirms the entire text passed validation.

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `return true;` |

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `text` | Field | The current contents of a numeric input control being validated. |
| `decimalCount` | Variable | Counter used to track whether a decimal separator has already been accepted. |
| `ch` | Variable | The current character being examined in the input string. |
| `Character.isDigit` | Technical API | Java standard library check that returns true when a character is a numeric digit. |
| decimal point `'.'` | Symbol | Fraction separator used in decimal numbers. |
| numeric input field | Business term | A UI field intended to accept only numbers, optionally with one decimal fraction. |
| validation guard | Technical term | A pre-check that prevents invalid user input from entering the application state. |
| intermediate editing state | Business term | A temporarily incomplete value, such as an empty field while the user is typing. |