---

# (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()

`NumericFilter.isValid(String text)` is a low-level validation routine that determines whether an input string is acceptable as a numeric value for the UI filter workflow. Its business purpose is to protect numeric-entry fields from invalid user input while still allowing an empty value, which typically represents a cleared field or an optional entry state. The method enforces a simple decimal format rule: only digits are allowed, and at most one period (`.`) may appear in the string. In effect, it acts as a shared gatekeeper for numeric text normalization before downstream UI logic accepts or rejects the value.

The method implements a compact routing/validation pattern rather than a transformation pattern: it first short-circuits on empty input, then iterates through each character to decide whether the value remains valid. The branch logic splits into three business outcomes: empty input is accepted, a single decimal separator is allowed, and any non-digit character causes immediate rejection. Because the implementation is self-contained and does not call external services or persistence layers, its role in the larger system is that of a reusable utility used by UI input filters and related validation paths.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START["isValid(text)"]
    CHECK_EMPTY{"text.isEmpty()?"}
    RETURN_TRUE_EMPTY["return true"]
    INIT_DECIMAL["decimalCount = 0"]
    LOOP_COND{"i < text.length()?"}
    GET_CHAR["ch = text.charAt(i)"]
    DECIMAL_CHECK{"ch == '.' and decimalCount != 1?"}
    INC_DECIMAL["decimalCount++"]
    DIGIT_CHECK{"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_COND
    LOOP_COND -->|Yes| GET_CHAR
    GET_CHAR --> DECIMAL_CHECK
    DECIMAL_CHECK -->|Yes| INC_DECIMAL
    DECIMAL_CHECK -->|No| DIGIT_CHECK
    DIGIT_CHECK -->|No| RETURN_FALSE
    DIGIT_CHECK -->|Yes| LOOP_COND
    INC_DECIMAL --> LOOP_COND
    LOOP_COND -->|No| RETURN_TRUE
```

**Constant resolution:** No constant files were referenced by this method. The validation logic uses literal character and JDK API checks only.

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `text` | `String` | Candidate numeric input value coming from the UI filter pipeline. It may contain digits, a single decimal point, or be empty. Empty input is treated as valid so the user can clear the field without triggering an error state. Any other character immediately makes the value invalid. |

**Instance fields / external state read:** None. This method uses only its input parameter and local variables.

## 4. CRUD Operations / Called Services

This method performs no CRUD operation and invokes no application service, DAO, or persistence method. Its work is limited to in-memory character inspection and immediate boolean return.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|-----------------------|
| - | - | - | - | No external read/write/update/delete activity; local validation only |

## 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: -

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | Internal method in `NumericFilter` | `NumericFilter.<caller at line 177>` -> `NumericFilter.isValid` | `-` |
| 2 | Internal method in `NumericFilter` | `NumericFilter.<caller at line 190>` -> `NumericFilter.isValid` | `-` |

## 6. Per-Branch Detail Blocks

**Block 1** — **IF** `(text.isEmpty())` (L195)

> Accepts an empty string as valid input so the UI can preserve a cleared numeric field without error handling.

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

**Block 2** — **ELSE** `(text is not empty)` (L197)

> Initializes the decimal separator counter and begins character-by-character inspection.

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

**Block 2.1** — **FOR** `(i < text.length())` (L198)

> Iterates through every character to enforce the numeric-only rule.

| # | Type | Code |
|---|------|------|
| 1 | SET | `char ch = text.charAt(i);` |

**Block 2.1.1** — **IF** `(ch == '.' && decimalCount != 1)` (L200)

> Allows a decimal point and increments the decimal separator counter.

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

**Block 2.1.2** — **ELSE IF** `(!Character.isDigit(ch))` (L202)

> Rejects any non-digit character other than the first accepted decimal separator.

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

**Block 3** — **RETURN** `(all characters passed validation)` (L205)

> Completes validation successfully when every character is either a digit or one allowed decimal point.

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

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `text` | Field | Input candidate supplied to the numeric filter; represents the current text typed or pasted into a numeric UI control. |
| `decimalCount` | Local variable | Counter used to allow at most one decimal separator in the candidate value. |
| `Character.isDigit()` | JDK API | Java digit-check utility used to confirm that each non-decimal character is a valid numeric digit. |
| decimal separator (`.`) | Business term | The period character used to represent fractional numeric values such as `12.5`. |
| numeric filter | UI term | Input validation layer that prevents invalid characters from entering a numeric field. |
| empty input | Business term | A cleared or optional field state that is accepted as valid by this method. |