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

| Field | Value |
|-------|-------|
| Fully Qualified Name | `io.github.biezhi.java11.string.Example` |
| Layer | Utility (Inferred from package: generic code example/showcase utility) |
| Module | `string` (Package: `io.github.biezhi.java11.string`) |

## 1. Role

### Example.demonstrateStringIsBlank()

This method is a code demonstration utility designed to showcase the `String.isBlank()` method introduced in JDK 11. It systematically constructs four distinct string values — an empty string, a string containing only the platform line separator, a string containing only a tab character, and a string containing only spaces — and prints the result of calling `isBlank()` on each one. The method serves no business operation; rather, it functions as an educational or reference artifact in the `java11.string` showcase package, which collects representative usages of Java 11 API additions. Its role in the larger system is purely illustrative: it prints diagnostic output that a developer or business analyst can read to understand which character sequences `String.isBlank()` considers blank, contrasting with `String.isEmpty()` which only detects zero-length strings. The method has no conditional branches, no external service calls, and no state mutation.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["demonstrateStringIsBlank()"])
    STEP1["writeHeader - String.isBlank()"]
    STEP2["emptyString = empty string"]
    STEP3["Print: emptyString.isBlank"]
    STEP4["onlyLineSeparator = line.separator"]
    STEP5["Print: onlyLineSeparator.isBlank"]
    STEP6["tabOnly = tab character"]
    STEP7["Print: tabOnly.isBlank"]
    STEP8["spacesOnly = spaces"]
    STEP9["Print: spacesOnly.isBlank"]
    END_NODE(["Return void"])

    START --> STEP1
    STEP1 --> STEP2
    STEP2 --> STEP3
    STEP3 --> STEP4
    STEP4 --> STEP5
    STEP5 --> STEP6
    STEP6 --> STEP7
    STEP7 --> STEP8
    STEP8 --> STEP9
    STEP9 --> END_NODE
```

The method executes a linear sequence of five phases with no branching:

1. **Header**: Calls `writeHeader("String.isBlank()")` to emit a section header identifying the demonstrated API.
2. **Empty string test**: Creates a zero-length string (`""`) and prints whether `isBlank()` returns true.
3. **Line separator test**: Retrieves the platform line separator via `System.getProperty("line.separator")` and prints whether `isBlank()` returns true.
4. **Tab character test**: Creates a single-tab string (`"\t"`) and prints whether `isBlank()` returns true.
5. **Spaces test**: Creates a string of three spaces (`"   "`) and prints whether `isBlank()` returns true.

All four test cases produce `true`, demonstrating that `String.isBlank()` considers any string composed entirely of Unicode whitespace (or zero length) as blank.

## 3. Parameter Analysis

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

This method takes no parameters. It constructs all test data internally.

**External state read:**

| # | Name | Type | Business Description |
|---|------|------|---------------------|
| 1 | `System.line.separator` | Platform property | The platform-specific line separator string (e.g., `
` on Unix, `\r
` on Windows), retrieved via `System.getProperty("line.separator")` |

## 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` — prints a section header |

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| - | `System.getProperty` | `System` | - | Reads the JVM system property `line.separator` to obtain the platform line separator string |
| - | `System.out.println` | `System` | - | Prints formatted output to standard output (console) |

This method performs no Create, Read, Update, or Delete operations on business data. It interacts only with the Java standard library (`System`, `String`) for demonstration purposes.

## 5. Dependency Trace

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | N/A | No callers found | - |

This method is not called by any other class in the codebase. It is a standalone demonstration method invoked manually or referenced in documentation/javadoc examples. The only other reference in the codebase is a commented-out call at line 110 of the same file.

## 6. Per-Branch Detail Blocks

> This method contains no conditional branches (no if/else, switch, loops, or try/catch). The flow is strictly linear. Each operation is documented below in sequential block order.

**Block 1** — EXEC `(writeHeader call)` (L80)

> Writes a section header to identify this demonstration.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `writeHeader("String.isBlank()")` // Prints a section header identifying the JDK 11 feature being demonstrated |

**Block 2** — SET + EXEC `(empty string test)` (L82–L83)

> Creates a zero-length string and tests whether `isBlank()` considers it blank. An empty string has no characters, so `isBlank()` returns `true`.

| # | Type | Code |
|---|------|------|
| 1 | SET | `emptyString = ""` // Empty string literal |
| 2 | EXEC | `System.out.println("空文字列 -> " + emptyString.isBlank())` // Prints Japanese label "空文字列" (empty string) followed by the blankness result |

**Block 3** — SET + EXEC `(line separator test)` (L85–L86)

> Retrieves the platform-specific line separator and tests blankness. Line separators are whitespace characters, so `isBlank()` returns `true`.

| # | Type | Code |
|---|------|------|
| 1 | SET | `onlyLineSeparator = System.getProperty("line.separator")` // Platform line separator (e.g., "
" on Unix, "\r
" on Windows) |
| 2 | EXEC | `System.out.println("改行文字 -> " + onlyLineSeparator.isBlank())` // Prints Japanese label "改行文字" (line separator character) followed by the blankness result |

**Block 4** — SET + EXEC `(tab character test)` (L88–L89)

> Creates a single-tab string and tests blankness. Tabs are whitespace characters, so `isBlank()` returns `true`.

| # | Type | Code |
|---|------|------|
| 1 | SET | `tabOnly = "\t"` // Single tab character |
| 2 | EXEC | `System.out.println("Tab 制御文字 -> " + tabOnly.isBlank())` // Prints Japanese label "Tab 制御文字" (tab control character) followed by the blankness result |

**Block 5** — SET + EXEC `(spaces test)` (L91–L92)

> Creates a string of three space characters and tests blankness. Spaces are whitespace characters, so `isBlank()` returns `true`.

| # | Type | Code |
|---|------|------|
| 1 | SET | `spacesOnly = "   "` // Three consecutive space characters |
| 2 | EXEC | `System.out.println("空白 -> " + spacesOnly.isBlank())` // Prints Japanese label "空白" (blank/whitespace) followed by the blankness result |

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `String.isBlank()` | JDK 11 API | A method on `java.lang.String` that returns `true` if the string is empty or contains only Unicode whitespace characters (spaces, tabs, line separators, etc.). Introduced in JDK 11 as a more capable replacement for checking emptiness compared to `String.isEmpty()`. |
| `String.isEmpty()` | JDK 1.0 API | The original method on `java.lang.String` that returns `true` only if the string length is zero. Does not treat whitespace-only strings as empty. |
| 空文字列 (kū moji ressetsu) | Japanese label | "Empty string" — the first test case, a `""` literal with zero characters |
| 改行文字 (kai gyō moji) | Japanese label | "Line separator character" — the second test case, a string containing only the platform line separator |
| Tab 制御文字 (Tab seigyō moji) | Japanese label | "Tab control character" — the third test case, a string containing only a tab character (`\t`) |
| 空白 (kuhaku) | Japanese label | "Blank/whitespace" — the fourth test case, a string containing only space characters |
| line.separator | JVM property | A standard Java system property whose value is the platform-specific line separator string (`
` on Linux/macOS, `\r
` on Windows) |
| writeHeader | Internal utility | A method in the `Example` class that prints a section header to the console, used to visually separate demonstration sections |