Field-Level Documentation in Java Classes

When maintaining large codebases, documenting field purposes direct in the source code becomes essential. Java provides Javadoc syntax specifically designed for this purpose.

Basic Syntax for Field Documentation

Field documentation uses block comments that begin with /** and end with */. These comments appear immediately before the field declaration they describe.

public class Product {
    /**
     * Unique identifier assigned to each product instance.
     * Format: alphanumeric string with maximum 12 characters.
     */
    private String productId;

    /**
     * Current retail price in USD.
     * Value must be non-negative.
     */
    private double price;

    /**
     * Quantity available in warehouse inventory.
     * Default value is 0.
     */
    private int stockQuantity;
}

Documentation Best Practices

Include semantic details: Describe what the field represents, not just its data type. Mention any constraints, default values, or format requirements that apply.

Avoid redundant type information: Writing @param String name when the field is private String name adds no value since the type is already visible in the code.

Document units and formats: When applicable, specify measurement units, date formats, or encoding schemes.

public class SensorReading {
    /**
     * Temperature measurement in Celsius degrees.
     * Range: -273.15 to 1000.00
     */
    private double temperature;

    /**
     * Timestamp in ISO 8601 format (yyyy-MM-dd'T'HH:mm:ss'Z').
     */
    private String timestamp;
}

Multi-Field Documentation Pattern

When multiple fields share a common purpose, group them logically within the class structure:

public class Order {
    // Identification fields
    /** Unique order number generated by the system. */
    private long orderNumber;

    /** Customer-provided reference code for external tracking. */
    private String customerReference;

    // Monetary fields
    /** Subtotal before applying discounts or taxes. */
    private BigDecimal subtotal;

    /** Total discount amount applied to this order. */
    private BigDecimal discount;
}

Generated Documentation Output

When Javadoc tools process these comments, they create HTML documentation where field descriptions appear in organized tables. This documentation remains synchronized with the source code as long as the comment are updated alongside field modifications.

Tools like Javadoc, JAutodoc for Eclipse, or IntelliJ IDEA's documentation generation features extract these block comments and format them for display in API documentation pages.