Encapsulation

Software Engineering 07 Sep 2026 10 min read

Keeping Behavior Close to Data with Tell, Don’t Ask

A class can hide its fields and still force every caller to understand its rules. The usual symptom is code that asks an object for several values, makes a decision with those values, and then tells the object what state to change. That design spreads knowledge. When the rule changes, every place that reconstructed the rule may need to change too. Tell, Don’t Ask is a design heuristic for reducing that problem. Instead of asking an object for internal information so another object can decide what should happen, tell the object the intent and let the component that owns the relevant rules make the decision.

Software Engineering Software Design

Software Engineering 05 Sep 2026 9 min read

Replace Query-Then-Act with Intention-Revealing Operations

An object can expose perfectly reasonable getters and still make a system difficult to change. The problem appears when callers repeatedly read those values, interpret them, and then decide which mutation is allowed. Suppose several parts of an application do this: if order.status == "pending" and order.paymentReceived: order.status = "confirmed" The caller is not merely using data. It knows the rule for confirming an order. If another caller needs the same behavior, that rule is likely to be copied. When the rule changes, every copy becomes a place that can disagree.

Software Engineering Software Design

Software Engineering 04 Sep 2026 9 min read

Limiting Object Navigation to Protect Encapsulation

A method can depend on far more of a system than its parameter list suggests. The warning sign is often a chain that reaches through one object to inspect several others: order.customer.address.country.code The expression is short, but the caller now knows that an order has a customer, the customer has an address, the address has a country, and the country exposes a code. A change anywhere along that path can force the caller to change even when the caller’s real question has not changed.

Software Engineering Software Design