# (DD11) Business Logic — Example.demonstrateStringIsBlank() [15 LOC]

| Field | Value |
|-------|-------|
| Fully Qualified Name | `io.github.biezhi.java11.string.Example` |
| Layer | Utility |
| Module | `string` (Package: `io.github.biezhi.java11.string`) |

## 1. Role

### Example.demonstrateStringIsBlank()

This method is a demonstration utility that illustrates the behavior of the JDK 11 `String.isBlank()` API across several representative text inputs. It is not a business transaction method in the traditional CRUD sense; instead, it acts as an educational sample that prints the evaluation result for multiple whitespace scenarios so developers can understand how the runtime classifies blank strings. The method first emits a section header, then evaluates an empty string, a platform line-separator value, a tab character, and a space-only string.

From a business-operation perspective, the method supports platform validation and developer education around text normalization rules. Its role in the larger system is a standalone example entry point used in a sample class that groups Java 11 string features. The implementation follows a simple sequential demonstration pattern: initialize a candidate string, invoke `isBlank()`, and print the outcome. There are no conditional branches, persistence operations, or external service calls.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["demonstrateStringIsBlank()"])
    H1(["writeHeader(\"String.isBlank()\")"])
    S1(["Set emptyString = \"\""])
    C1(["Print blank check for empty string"])
    S2(["Set onlyLineSeparator = System.getProperty(\"line.separator\")"])
    C2(["Print blank check for line separator"])
    S3(["Set tabOnly = \"\\t\""])
    C3(["Print blank check for tab"])
    S4(["Set spacesOnly = \"   \""])
    C4(["Print blank check for spaces"])
    END(["Return"])
    START --> H1
    H1 --> S1
    S1 --> C1
    C1 --> S2
    S2 --> C2
    C2 --> S3
    S3 --> C3
    C3 --> S4
    S4 --> C4
    C4 --> END
```

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| - | (none) | - | - |

Instance fields / external state read by this method:
- `System.getProperty("line.separator")` reads the JVM line-separator property from the runtime environment.
- No instance fields are read or modified.

## 4. CRUD Operations / Called Services

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

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| - | `Example.writeHeader` | Example | - | Calls `writeHeader` in `Example` |

This method does not perform database CRUD. It only invokes local utility methods and JDK library APIs.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| - | `Example.writeHeader` | Example | - | Writes the sample section header for the console demo |
| - | `System.getProperty` | JDK | JVM system property `line.separator` | Reads the platform line-separator configuration |
| - | `String.isBlank` | JDK | - | Evaluates whether each sample string contains only whitespace |
| - | `System.out.println` | JDK | Console output | Prints the computed demonstration result |

## 5. Dependency Trace

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 | Screen:Example | `Example.main` -> `Example.demonstrateStringIsBlank` | `System.getProperty [R] JVM line.separator` |
| 2 | Documentation reference | `.codewiki/io/github/biezhi/java11/string.md` -> `Example.demonstrateStringIsBlank` | `String.isBlank [R] -` |

Notes:
- The repository search did not find additional Java callers for `demonstrateStringIsBlank(`.
- The method is effectively self-contained and has no downstream business-service dependencies.

## 6. Per-Branch Detail Blocks

**Block 1** — [SEQUENCE] `(method entry)` (L79)

> Initialize the console demonstration for `String.isBlank()`.

| # | Type | Code |
|---|------|------|
| 1 | CALL | `writeHeader("String.isBlank()");` |

**Block 2** — [SEQUENCE] `(empty string sample)` (L81-L82)

> Demonstrates that an empty string is considered blank.

| # | Type | Code |
|---|------|------|
| 1 | SET | `String emptyString = "";` |
| 2 | EXEC | `System.out.println("空字符串    -> " + emptyString.isBlank());` |

**Block 3** — [SEQUENCE] `(line separator sample)` (L84-L85)

> Demonstrates how the current platform line separator is treated by `isBlank()`.

| # | Type | Code |
|---|------|------|
| 1 | SET | `String onlyLineSeparator = System.getProperty("line.separator");` |
| 2 | EXEC | `System.out.println("换行符     -> " + onlyLineSeparator.isBlank());` |

**Block 4** — [SEQUENCE] `(tab sample)` (L87-L88)

> Demonstrates that a tab-only string is considered blank.

| # | Type | Code |
|---|------|------|
| 1 | SET | `String tabOnly = "\t";` |
| 2 | EXEC | `System.out.println("Tab 制表符 -> " + tabOnly.isBlank());` |

**Block 5** — [SEQUENCE] `(spaces-only sample)` (L90-L91)

> Demonstrates that a spaces-only string is considered blank.

| # | Type | Code |
|---|------|------|
| 1 | SET | `String spacesOnly = "   ";` |
| 2 | EXEC | `System.out.println("空格       -> " + spacesOnly.isBlank());` |

**Block 6** — [RETURN] `(method exit)` (L92-L93)

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `}` |

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `String.isBlank()` | Technical API | JDK 11 string predicate that returns `true` when a string is empty or contains only whitespace characters |
| `writeHeader` | Utility method | Console formatting helper that prints the title of the demonstration section |
| `line.separator` | JVM property | Platform-specific newline sequence used by the current runtime |
| `emptyString` | Local variable | Sample input representing a zero-length string |
| `onlyLineSeparator` | Local variable | Sample input representing the JVM newline sequence |
| `tabOnly` | Local variable | Sample input representing a single tab character |
| `spacesOnly` | Local variable | Sample input representing a string made only of spaces |
| `System.out.println` | JDK API | Standard console output used to display example results |
| `JDK 11` | Platform term | Java Development Kit version 11, which introduced `String.isBlank()` |
| `blank` | Business term | Text containing no visible characters, or only whitespace |
| `whitespace` | Business term | Space-like characters such as spaces, tabs, and line breaks |
| `Utility` | Layer | A helper-style class or method used for demonstration and formatting rather than domain persistence |