Effective Commenting Strategies

Effective Commenting Strategies

Good comments explain the "why" behind code, not the "what." Use these strategies to write comments that enhance code maintainability without creating maintenance burden.

When to Use

• Adding comments to new code
• Reviewing existing comments for quality
• Establishing team commenting standards
• Optimizing comment density for readability
• Handling performance-sensitive code with comments

Core Principle: Intent Over Repetition

Good comments should:

• Not repeat code or explain what the code does
• Clarify intent at a higher abstraction level than the code
• Act as navigation like book headings or table of contents
• Help maintenance by explaining the original programmer's intent
• **Be efficient"—reading one English comment is faster than parsing 20 lines of code

Rule: If the code already explains everything, a comment that repeats it provides no value.

Comment Types

Marker Comments

Purpose: Remind developers of incomplete work (not intended for production)

Requirements:

• Use standardized markers (e.g., ***, TBD, TODO)
• Make markers mechanically searchable
• Include in release checklist to prevent shipping known defects

Action: Search for all markers before release to ensure no incomplete code ships.

Explanatory Comments

Purpose: Explain complex, tricky, or sensitive code

Strategy:

• If code is complex enough to need explanation, refactor the code first
• Make the code itself clearer
• Then use summary or intent comments if still needed

Summary Comments

Purpose: Condense several lines of code into one or two sentences

Value: More valuable than code-repeating comments because readers can scan them faster than reading code

When to use: Particularly helpful when non-original authors need to modify code

Intent Comments

Purpose: Explain the purpose of a code section at the intent/​problem level

Level: Operates more at the problem level than the solution level

Example:

• Intent: "Get current employee information"
• Solution/​Summary: "Update employeeRecord object"

Metadata Comments

Purpose: Record information that cannot be expressed in code

Includes:

• Copyright notices
• Confidentiality statements
• Version numbers
• Design notes
• Requirement references
• Online reference pointers
• Optimization notes
• Tool-required comments (e.g., Javadoc)

Maintainable Comment Style

Avoid High-Maintenance Styles

Do not use styles that require manual alignment:

• ❌ Leader dots (...) connecting variables and descriptions
• ❌ Asterisk boxes (*) surrounding paragraphs—requires adjusting both sides
• ❌ Plus-sign underlines (+---+)—requires precise positioning when text length changes

Principle: Prefer accurate comments over pretty comments. If maintaining aesthetics requires tedious work, abandon that style.

Syntax Guidelines

For Java and C++:

• Single-line comments: Use // syntax, keep comments short
• Multi-line comments: Use /​* ... */ syntax—easier to maintain than manually wrapped // lines

For emphasis: Use standard-length lines (via editor macros), not lines that vary with comment length

Comment Density Guidelines

Optimal Density

IBM Research Finding: Approximately 1 comment per 10 statements maximizes code clarity

• Below this density: Code becomes difficult to understand
• Above this density: Readability decreases

Avoid Quotas

Do not enforce rigid standards like "at least 1 comment per 5 lines"

Reason: This addresses the symptom (lack of comments) without solving the root cause (unclear code)

Performance Considerations

Principle: Do not avoid comments due to performance concerns (e.g., interpreted environments, network transmission overhead)

Solution: Create a separate release build

Implementation: Run a tool during the build process to automatically strip comments from the production version

Pseudocode Programming Process (PPP) Comment Efficiency

When using the Pseudocode Programming Process:

1. Recognize the pattern: Effective PPP naturally results in "a comment every few lines"
2. Understand the nature: Comment quantity is a side effect of the process, not a goal
3. Focus on efficiency: Don't count comments—evaluate whether each comment is effective
4. Assess sufficiency: Comments are sufficient if they:
   • Describe why the code was written
   • Meet the other standards in this skill

Conclusion: If comments explain "why" and meet quality standards, the quantity is adequate—don't worry about the number.