# (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 local input-validation routine used by the numeric filter to decide whether a candidate text value can be accepted as a valid numeric entry. The method performs a lightweight character-by-character validation rather than parsing the entire string into a number, which keeps the check fast and suitable for real-time UI filtering. It accepts empty input as valid, allowing the user to clear the field or continue typing without immediate rejection. For non-empty values, it permits digits and at most one decimal point, making it suitable for decimal-number entry in a text field. Any other character causes the method to fail validation immediately. In the larger system, this method acts as a shared utility inside the `NumericFilter` UI helper and supports interactive data entry by preventing invalid characters from reaching the model.

The method implements a simple validation-and-short-circuit pattern: it first handles the empty-string case, then iterates through each character and returns early when an invalid character is found. The two branch conditions cover the only accepted numeric formats here: an empty value and a decimal number with one optional `.` separator. There are no external service calls, persistence actions, or data mutations beyond the local loop counter and decimal counter.

## 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_CHECK{"i < text.length() ?")
GET_CHAR(["ch = text.charAt(i)"])
DOT_CHECK{"ch == '.' and decimalCount != 1 ?"}
INC_DECIMAL(["decimalCount++"])
DIGIT_CHECK{"Character.isDigit(ch) ?"}
RETURN_FALSE(["return false"])
NEXT_I(["i++"])
RETURN_TRUE_END(["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 --> DOT_CHECK
DOT_CHECK -->|Yes| INC_DECIMAL
DOT_CHECK -->|No| DIGIT_CHECK
DIGIT_CHECK -->|No| RETURN_FALSE
DIGIT_CHECK -->|Yes| NEXT_I
INC_DECIMAL --> NEXT_I
NEXT_I --> LOOP_CHECK
LOOP_CHECK -->|No| RETURN_TRUE_END
```

**CRITICAL — Constant Resolution:**
No constants are referenced by this method. The validation logic uses only literal checks for `''`-empty input, `'.'` decimal separator, and `Character.isDigit(...)`.

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `text` | `String` | User-entered candidate value for a numeric UI field. It may be empty, contain digits, or include a single decimal point. Any other character makes the input invalid and blocks acceptance by the filter. |

**Instance fields / external state read:** None. The method uses only the incoming argument and local variables.

## 4. CRUD Operations / Called Services

This method does not call any external business service, controller, DAO, or CRUD endpoint. It performs in-memory validation only.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|-----------------------|
| - | - | - | - | No persistence or service access; pure input validation |

## 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: -

`NumericFilter.isValid(String)` is called from two locations inside the same `UI.java` file, both as part of the numeric filtering workflow.

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | Utility: `UI` inner logic | `UI` numeric-input handling -> `isValid(sb.toString())` -> `NumericFilter.isValid` | None |
| 2 | Utility: `UI` inner logic | `UI` numeric-input handling -> `isValid(sb.toString())` -> `NumericFilter.isValid` | None |

## 6. Per-Branch Detail Blocks

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

> Accepts blank input so the user can clear the field or continue editing without triggering a validation failure.

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

**Block 2** — ELSE (L199)

> Initializes decimal tracking before scanning the text one character at a time.

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

**Block 2.1** — FOR loop body `(i < text.length())` (L200)

| # | Type | Code |
|---|------|------|
| 1 | SET | `char ch = text.charAt(i);` |
| 2 | IF | `if (ch == '.' && decimalCount != 1) {` |

**Block 2.1.1** — IF `(ch == '.' && decimalCount != 1)` (L202)

| # | Type | Code |
|---|------|------|
| 1 | SET | `decimalCount++;` |
| 2 | NEXT | `continue to next loop iteration` |

**Block 2.1.2** — ELSE IF `(!Character.isDigit(ch))` (L203)

> Rejects any character that is neither the allowed decimal separator nor a digit.

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

**Block 2.1.3** — ELSE (valid digit path) (L203)

| # | Type | Code |
|---|------|------|
| 1 | LOOP | `advance to next character` |

**Block 3** — AFTER LOOP (L208)

> If the loop completes without encountering an invalid character, the text is treated as a valid numeric value.

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

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `text` | Field | Candidate input string being validated for numeric entry in the UI. |
| `decimalCount` | Variable | Local counter used to ensure the input contains at most one decimal point. |
| `.` | Symbol | Decimal separator permitted in numeric input. |
| `Character.isDigit` | Java API | Standard character classification used to allow numeric digits only. |
| NumericFilter | Class | UI-side input filter that constrains text entry to numeric values. |
| UI | Class/module | Swing user-interface class containing the numeric validation helper. |
| `isValid` | Method | Validation method that accepts empty strings and decimal numeric text while rejecting all other characters. |