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

| Field | Value |
|-------|-------|
| Fully Qualified Name | `io.github.biezhi.java11.string.Example` |
| Layer | Utility (inferred from package `io.github.biezhi.java11.string` — a JDK feature showcase library) |
| Module | `string` (Package: `io.github.biezhi.java11.string`) |

## 1. Role

### Example.demonstrateStringIsBlank()

This method is a standalone demonstration utility that showcases the `String.isBlank()` method introduced in JDK 11. It serves as a live example within the *Java 11 String API* showcase project (`java-simple-advanced-examples` by biezi), used to verify and display how `String.isBlank()` correctly identifies various forms of "blank" content — including empty strings, whitespace-only strings, line separators, tab characters, and multi-space strings. It implements no conditional branching or business routing; instead, it follows a linear sequence: printing a section header, declaring several string constants, and printing the result of calling `isBlank()` on each. Its role in the larger system is that of a **developer-facing tutorial entry point** — one of many `demonstrateXxx()` methods in the `Example` class that serve as runnable examples for learning JDK 11 features. There are no callers outside of the file itself; the method is intentionally commented out in the main `main` method (line 110) and is expected to be run directly or via an IDE.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["demonstrateStringIsBlank()"])
    WRITE_HEADER["writeHeader(\"String.isBlank()\")"]
    EMPTY_STR["emptyString = \"\" (empty string literal)"]
    PRINT_EMPTY["System.out.println(空文字列 -> emptyString.isBlank())"]
    LINE_SEP["onlyLineSeparator = System.getProperty(\"line.separator\")"]
    PRINT_LINE_SEP["System.out.println(改行符 -> onlyLineSeparator.isBlank())"]
    TAB_STR["tabOnly = \"\\t\" (tab character literal)"]
    PRINT_TAB["System.out.println(Tab 制表符 -> tabOnly.isBlank())"]
    SPACE_STR["spacesOnly = \"   \" (three-space string literal)"]
    PRINT_SPACE["System.out.println(空白 -> spacesOnly.isBlank())"]
    END_NODE(["Return / Next"])

    START --> WRITE_HEADER
    WRITE_HEADER --> EMPTY_STR
    EMPTY_STR --> PRINT_EMPTY
    PRINT_EMPTY --> LINE_SEP
    LINE_SEP --> PRINT_LINE_SEP
    PRINT_LINE_SEP --> TAB_STR
    TAB_STR --> PRINT_TAB
    PRINT_TAB --> SPACE_STR
    SPACE_STR --> PRINT_SPACE
    PRINT_SPACE --> END_NODE
```

**CRITICAL — Constant Resolution:**
No external constants are referenced in this method. All string literals are inline. No conditional branches exist.

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| - | (none) | - | This method takes no parameters. It operates entirely on inline string literals and system properties. |

**Inline variables and their business meaning:**

| Variable | Type | Business Description |
|----------|------|---------------------|
| `emptyString` | `String` | An empty string literal `""` — used to verify `isBlank()` returns `true` for zero-length content. |
| `onlyLineSeparator` | `String` | The platform's line separator (e.g., `
` on Unix, `\r
` on Windows) — used to verify `isBlank()` correctly identifies line-break-only content as blank. |
| `tabOnly` | `String` | A single tab character `"\t"` — used to verify `isBlank()` recognizes whitespace control characters. |
| `spacesOnly` | `String` | A three-space string `"   "` — used to verify `isBlank()` detects simple space-only content as blank. |

## 4. CRUD Operations / Called Services

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

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| - | `Example.writeHeader` | Example | - | Prints a section header for the demonstration output |
| - | `System.out.println` | JRE | - | Prints result strings to standard output |
| - | `System.getProperty` | JRE | - | Reads the platform line separator system property |

This method performs **no database or entity operations**. It is a pure console-output demonstration. No Create, Read, Update, or Delete operations against any persistent storage occur.

## 5. Dependency Trace

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | (none) | *(no callers found — method is commented out at Example.java:110)* | *(none — method performs no CRUD)* |

The only reference to `demonstrateStringIsBlank()` in the entire codebase is a commented-out call at line 110 of `Example.java`, which is the class's `main` method. The method is currently **not invoked** at runtime. It is designed to be executed manually, e.g., via an IDE's "run method" feature or by uncommenting the call in `main`.

## 6. Per-Branch Detail Blocks

This method contains **no conditional branches** (no if/else, switch, loops). It is a linear sequence of statements. Each statement is documented below as a sequential block.

**Block 1** — [EXEC] (L79–80)

> Print the section header for the `String.isBlank()` demonstration.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `writeHeader("String.isBlank()");` // Prints a formatted section header |

**Block 2** — [EXEC] (L82–83)

> Create an empty string literal and verify `isBlank()` returns `true`.

| # | Type | Code |
|---|------|------|
| 1 | SET | `emptyString = "";` // Empty string literal |
| 2 | EXEC | `System.out.println("空文字列   -> " + emptyString.isBlank());` // Prints "空文字列    -> true" |

**Block 3** — [EXEC] (L85–86)

> Fetch the platform's line separator and verify `isBlank()` returns `true`.

| # | Type | Code |
|---|------|------|
| 1 | SET | `onlyLineSeparator = System.getProperty("line.separator");` // Platform-specific line break (
 or \r
) |
| 2 | EXEC | `System.out.println("改行符     -> " + onlyLineSeparator.isBlank());` // Prints "改行符     -> true" |

**Block 4** — [EXEC] (L88–89)

> Create a tab-only string and verify `isBlank()` returns `true`.

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

**Block 5** — [EXEC] (L91–92)

> Create a multi-space string and verify `isBlank()` returns `true`.

| # | Type | Code |
|---|------|------|
| 1 | SET | `spacesOnly = "   ";` // Three-space string literal |
| 2 | EXEC | `System.out.println("空白       -> " + spacesOnly.isBlank());` // Prints "空白       -> true" |

## 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 whitespace characters (spaces, tabs, newlines, etc.). Introduced in JDK 11 as an improvement over `StringUtils.isEmpty()`. |
| 空文字列 | Japanese term | "Empty string" — a string with zero characters (`""`). `isBlank()` returns `true`. |
| 改行符 | Japanese term | "Line separator" / "Line break" — platform-specific newline character(s). `isBlank()` returns `true` when the string contains only line separators. |
| 制表符 | Japanese term | "Tab character" — the `\t` whitespace control character. `isBlank()` returns `true`. |
| 空白 | Japanese term | "Whitespace" / "Blank" — a string containing only space characters. `isBlank()` returns `true`. |
| `writeHeader` | Utility method | A helper method in the same `Example` class that prints a formatted section header to `System.out` for demo purposes. |
| `line.separator` | System property | A JVM system property holding the platform's line separator string (`"
"` on Unix/Linux, `"\r
"` on Windows). |
| JDK 11 | Product | Java Development Kit version 11 (released September 2018), which introduced `String.isBlank()` as part of the String API enhancements. |