---

# (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 client-side numeric text validation for UI input handling. Its business purpose is to determine whether a candidate string can be treated as a valid numeric value for a screen field, allowing either an empty value or a sequence composed only of digits with at most one decimal point. In practical terms, it acts as a reusable guard that prevents invalid characters from being accepted into numeric entry controls.

The method implements a lightweight validation/dispatch pattern: it first resolves the special case for empty input, then iterates through every character to enforce digit-only content with a limited decimal format. The single branching rule set covers two business outcomes: accept a blank value as valid input, or reject any string that contains a non-digit character other than a permitted decimal separator. This class-level logic is shared infrastructure for the UI layer and is not tied to any database, service component, or transaction flow.

## 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"])
    INIT_LOOP(["for i from 0 to text.length - 1"])
    GET_CHAR(["char ch = text.charAt(i)"])
    CHECK_DOT{"ch == '.' and decimalCount != 1?")
    INC_DECIMAL(["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 --> INIT_LOOP
    INIT_LOOP --> GET_CHAR
    GET_CHAR --> CHECK_DOT
    CHECK_DOT -- "Yes" --> INC_DECIMAL
    CHECK_DOT -- "No" --> CHECK_DIGIT
    INC_DECIMAL --> INIT_LOOP
    CHECK_DIGIT -- "Yes" --> INIT_LOOP
    CHECK_DIGIT -- "No" --> RETURN_FALSE
    INIT_LOOP --> RETURN_TRUE
```

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `text` | `String` | The user-entered numeric candidate value from a UI field. It may be blank, a whole number, or a decimal-style value. The method accepts blank input as valid, accepts digits with at most one decimal point, and rejects any other character pattern. |

Instance fields or external state read by this method: none.

## 4. CRUD Operations / Called Services

This method does not invoke any other business methods, service components, repository methods, or database operations. It performs in-memory validation only.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| - | - | - | - | No external CRUD or persistence interaction; the method only inspects the input string and returns a boolean verdict. |

## 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 | Screen: `UI.java` internal caller | `UI.java` line 177 -> `isValid(String text)` | `-` |
| 2 | Screen: `UI.java` internal caller | `UI.java` line 190 -> `isValid(String text)` | `-` |

## 6. Per-Branch Detail Blocks

**Block 1** — IF `(text.isEmpty())` (L197)

> Validates the empty-input special case and allows the field to remain blank.

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

**Block 2** — SET `(initialize decimal tracking)` (L201)

> Prepares the decimal separator counter before scanning the input string.

| # | Type | Code |
|---|------|------|
| 1 | SET | `byte decimalCount = 0;` |

**Block 3** — FOR `(i < text.length())` (L202)

> Iterates through each character in the candidate numeric text.

| # | Type | Code |
|---|------|------|
| 1 | SET | `char ch = text.charAt(i);` |
| 2 | IF | `if (ch == '.' && decimalCount != 1)` |
| 3 | SET | `decimalCount++;` |
| 4 | ELSE-IF | `else if (!Character.isDigit(ch))` |
| 5 | RETURN | `return false;` |

**Block 3.1** — IF `(ch == '.' && decimalCount != 1)` (L204)

> Accepts the first decimal point and counts it so additional decimal points can be rejected.

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

**Block 3.2** — ELSE-IF `(!Character.isDigit(ch))` (L206)

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

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

**Block 4** — RETURN `(all characters accepted)` (L209)

> Completes validation successfully after every character passes the digit/decimal rule.

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

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `text` | Field | User-entered candidate value being validated for numeric formatting in a UI control. |
| `decimalCount` | Technical variable | Counter used to track how many decimal separators have been encountered while scanning the input. |
| `Character.isDigit` | Technical API | Java standard-library digit check used to confirm that a character is numeric. |
| decimal point (`.`) | Business term | Allowed separator for decimal-form numeric entry. |
| numeric input validation | Business term | UI-level rule enforcement that prevents invalid characters from being accepted into a number field. |
| UI | Technical layer | Presentation-layer components that collect and validate user input before downstream processing. |