Mental Model: TUI Spreadsheet in Java

Spreadsheets feel mysterious until you stop thinking in grids and start thinking in cell keys + evaluation rules.

The Core Model

This spreadsheet is really two systems:

1. Storage system: Map<String, String> from cell key to raw content.
2. Evaluation system: turn raw content into display value.

Raw might be 42 or =A1+B1. Value is what users see.

Why Key-Value Beats 2D Arrays Here

For beginners, sparse storage is easier.

• Only store cells the user set.
• A1 is just a normalized string key.
• No need to pre-create giant tables.

In Java, HashMap is a perfect fit for this mental model.

Formula Thinking

Formula evaluation is a small parser problem.

• Strip spaces.
• Split on +.
• Resolve each token as number or cell reference.
• Return error markers when invalid.

You’re not building Excel. You’re building one clean rule at a time.

Java-Specific Insight

Java pushes explicit validation, which is good here.

• normalizeCell protects your storage layer.
• numberValue isolates conversion logic.
• evaluate isolates formula rules.

That separation keeps bugs local and fixable.

Debugging Strategy

When output looks wrong, inspect in this order:

1. normalized cell key
2. raw stored value
3. evaluated tokens
4. final computed result

Most spreadsheet bugs are just one bad step in that chain.

Extension Path

Good next features:

• subtraction and multiplication
• circular reference detection
• CSV import/export

Add one feature, then re-run your model: “store raw, evaluate safely, show value.”