Building Applications with Spring 5 and Vue.js 2

The Open-Closed Principle (OCP)

A software artifact should be open for extension but closed for modification.

Bertrand Meyer coined the OCP in 1988, providing us with guidance on how to create a design that is stable in the face of changes.

Here, we're going to borrow the DrawAllShapes example from Agile Software Development: Principles, Patterns, and Practices, to explain this principle here. We will write the example in ES6; the unrelated details have been omitted:

class Circle extends Shape { constructor(radius, point) {    this.type = 'circle'     // ...  }}class Square extends Shape {  constructor(width, point) {    this.type = 'square'    // ...  }}function drawCircle(circle) {  // Draw circle logic here}function drawSquare(square) { // Draw square ...