Interface Segregation Principle

Prefer small, focused interfaces so classes only provide what they need.

What is Interface Segregation Principle?

The Interface Segregation Principle says to prefer several small interfaces over one big one, so classes aren't forced to provide methods they don't need.

// Instead of one IMachine with Print, Scan and Fax:
public interface IPrinter { void Print(string doc); }
public interface IScanner { string Scan(); }

public class BasicPrinter : IPrinter { public void Print(string doc) { } }

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Updated September 27, 2026