---

# (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 presentation-oriented demonstration routine that showcases the JDK 11 `String.isBlank()` capability using a set of representative string values. Its business purpose is to validate and explain how the platform distinguishes between visually empty text and text that contains whitespace characters only, which is important in input validation, user-facing examples, and developer education. The method does not transform persisted data or invoke downstream business workflows; instead, it prints the boolean outcome of `isBlank()` for four sample cases so the caller can observe the runtime behavior directly.

The method follows a simple sequential demonstration pattern: it first emits a section header, then evaluates an empty string, a line-separator value, a tab-only string, and a spaces-only string. Each sample represents a different whitespace category that may appear in real-world text fields. Because the method is self-contained and has no branching, it acts as a didactic utility inside the `Example` class rather than as a reusable domain service.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START["demonstrateStringIsBlank()"]
    N1["Call writeHeader(\"String.isBlank()\")"]
    N2["Set emptyString = \"\""]
    N3["Print emptyString.isBlank() result"]
    N4["Set onlyLineSeparator = System.getProperty(\"line.separator\")"]
    N5["Print onlyLineSeparator.isBlank() result"]
    N6["Set tabOnly = \"\\t\""]
    N7["Print tabOnly.isBlank() result"]
    N8["Set spacesOnly = \"   \""]
    N9["Print spacesOnly.isBlank() result"]
    END["Return"]
    START --> N1
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5
    N5 --> N6
    N6 --> N7
    N7 --> N8
    N8 --> N9
    N9 --> END
```

## 3. Parameter Analysis

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

This method accepts no parameters. It reads one JVM system property, `line.separator`, and uses only local constants and standard output as its runtime context.

## 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` |

Analyze all method calls within this method and classify each as a CRUD operation.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| R | `Example.writeHeader` | Example | - | Writes a console header for the demonstration section |
| R | `String.isBlank` | JDK 11 String API | - | Evaluates whether the sample string is empty or contains only whitespace |
| R | `System.getProperty` | JDK System API | JVM property `line.separator` | Retrieves the platform line-separator value used as the whitespace example |
| R | `System.out.println` | JDK System API | Console output | Outputs the boolean result for each sample string |

## 5. Dependency Trace

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | `Example.main(String[] args)` | `Example.main(String[] args)` -> `Example.demonstrateStringIsBlank()` | `String.isBlank [R] whitespace example` |

The only discovered caller is the `main` method in the same `Example` class, and the invocation is commented out in source. No external Screen, Batch, or CBS caller was found in the Java source set searched.

## 6. Per-Branch Detail Blocks

Because the method contains no conditional branches, loops, or exception handlers, the execution flow is linear and can be documented as a single top-level block sequence.

**Block 1** — [SEQUENTIAL] (L79-L93)

> Demonstration setup and whitespace evaluation for four sample string values.

| # | Type | Code |
|---|------|------|
| 1 | CALL | `writeHeader("String.isBlank()");` |
| 2 | SET | `String emptyString = "";` |
| 3 | EXEC | `System.out.println("空字符串    -> " + emptyString.isBlank());` // prints whether an empty string is blank |
| 4 | SET | `String onlyLineSeparator = System.getProperty("line.separator");` |
| 5 | EXEC | `System.out.println("换行符     -> " + onlyLineSeparator.isBlank());` // prints whether a line separator is blank |
| 6 | SET | `String tabOnly = "\t";` |
| 7 | EXEC | `System.out.println("Tab 制表符 -> " + tabOnly.isBlank());` // prints whether a tab-only string is blank |
| 8 | SET | `String spacesOnly = "   ";` |
| 9 | EXEC | `System.out.println("空格       -> " + spacesOnly.isBlank());` // prints whether a spaces-only string is blank |
| 10 | RETURN | `}` |

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `String.isBlank()` | Technical API | JDK 11 string utility that returns `true` when a string is empty or contains only whitespace characters |
| `line.separator` | JVM property | Platform-specific line separator value, such as newline characters used by the operating system |
| `writeHeader` | Utility method | Local helper that prints a section title before the sample output |
| `空字符串` | UI label | Empty string example used to show that zero-length text is considered blank |
| `换行符` | UI label | Line-separator example used to show that newline-only text is considered blank |
| `Tab 制表符` | UI label | Tab character example used to show that tab-only text is considered blank |
| `空格` | UI label | Space-only example used to show that whitespace-only text is considered blank |
| `whitespace` | Technical term | Characters such as spaces, tabs, and line separators that do not represent visible content |
| JDK 11 | Platform term | Java Development Kit version 11, which introduced `String.isBlank()` |