miliare / hoover-ocp

Hoover kata to explain Open Closed Principle

SOLID : Open Closed Principle

Forked from xke-solid https://github.com/xebia-france/xke-solid

Why?

public void clean() {
  for (int i = 0 ; i < program.length() ; i++) {
    switch (program.charAt(i)) {
      case('A'):
        goForward();
        break;
      case('D'):
        turnRight();
        break;
      case('G'):
        turnLeft();
        break;
      default:
        throw new IllegalArgumentException("Invalid command: " + program.charAt(i));
    }
  }
}

When adding a new command changes multiple classes like adding one new Command and updating the already created class Hoover, the class which runs the program, you should stop and think.

Definition :

Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification

Which means: keep as much as possible existing code unchanged when adding new functionality.

How?

Most of the use cases involves inheritance and polymorphism but you can also use patterns like Decorator, Factory or Observer.