---

# (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 input validation for numeric text entered into the UI layer. Its business purpose is to decide whether a candidate value can be treated as a numeric input before the application accepts or displays it, which is typically used to guard user-driven text entry in a form or filter control. The method supports two acceptance paths: an empty string is considered valid, and non-empty strings are valid only when they contain digits and at most one decimal point. It behaves as a lightweight validation rule rather than a transformation or persistence routine, so its role is to prevent invalid values from propagating into downstream UI or business logic. The implementation uses a simple routing pattern: it short-circuits on empty input, then scans each character and rejects the value immediately when a non-numeric character appears outside the allowed decimal point rule. In the larger system, this method acts as a shared utility inside the UI class, protecting numeric entry points from malformed text without introducing any external service dependency.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
START(["isValid(text)"])
CHECK_EMPTY{"text.isEmpty()?"}
RETURN_TRUE1(["return true"])
INIT_DECIMAL["decimalCount = 0"]
FOR_LOOP{"for each character in text"}
GET_CHAR["char ch = text.charAt(i)"]
CHECK_DOT{"ch == '.' and decimalCount != 1?"}
INCREMENT_DECIMAL["decimalCount++"]
CHECK_DIGIT{"Character.isDigit(ch)?"}
RETURN_FALSE(["return false"])
RETURN_TRUE2(["return true"])
END_NODE(["End"])
START --> CHECK_EMPTY
CHECK_EMPTY -->|Yes| RETURN_TRUE1
CHECK_EMPTY -->|No| INIT_DECIMAL
RETURN_TRUE1 --> END_NODE
INIT_DECIMAL --> FOR_LOOP
FOR_LOOP --> GET_CHAR
GET_CHAR --> CHECK_DOT
CHECK_DOT -->|Yes| INCREMENT_DECIMAL
CHECK_DOT -->|No| CHECK_DIGIT
INCREMENT_DECIMAL --> FOR_LOOP
CHECK_DIGIT -->|Yes| FOR_LOOP
CHECK_DIGIT -->|No| RETURN_FALSE
RETURN_FALSE --> END_NODE
FOR_LOOP --> RETURN_TRUE2
RETURN_TRUE2 --> END_NODE
```

**Constant resolution note:** no project constants are referenced in this method.

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `text` | `String` | User-entered candidate value for a numeric UI field or filter. It may be empty, contain digits, and may include a single decimal point; any other character causes validation to fail. |

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

## 4. CRUD Operations / Called Services

This method does not call any external services, persistence operations, or CRUD-oriented business methods. It performs only in-memory validation with local control flow.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|-----------------------|
| - | - | - | - | No database, service-component, or CRUD 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: -

The only callers found in the source file are internal invocations from the same `UI.java` class, which call `isValid(sb.toString())` before allowing numeric text to be accepted.

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

## 6. Per-Branch Detail Blocks

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

> Validates the empty-input case and accepts it as a permissible value.

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

**Block 2** — SET / FOR `(initialize decimalCount and scan text)` (L199-L207)

> Initializes decimal tracking and iterates through every character in the input.

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

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

> Allows one decimal separator and counts it for subsequent validation.

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

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

> Rejects any character that is neither the approved decimal point nor a digit.

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

**Block 3** — RETURN `(all characters processed)` (L207)

> Accepts the text after a complete successful scan.

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

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|-------------------|
| `text` | Field | Candidate UI input value being validated as numeric text. |
| `decimalCount` | Technical term | Local counter that tracks how many decimal points have been seen in the input. |
| `Character.isDigit` | Technical API | Java standard library check that confirms whether a character is a numeric digit. |
| decimal point | Business term | The `.` character used to represent fractional numeric values in user input. |
| numeric filter | Business term | UI validation rule that restricts input to numeric characters only. |
| UI | Acronym | User Interface — the presentation layer where users enter or view data. |
| validation | Business term | A control step that confirms user input meets allowed format rules before acceptance. |