Adapter Design Pattern
Overview
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Terminology
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Adapter UML Diagram
Source Code
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./src/adapter/adapter-concept.ts
// Adapter Concept Sample Code
interface IA {
methodA(): void
}
class ClassA implements IA {
methodA() {
console.log('method A')
}
}
interface IB {
methodB(): void
}
class ClassB implements IB {
methodB() {
console.log('method B')
}
}
class ClassBAdapter implements IA {
// ClassB does not have a methodA, so we can create an adapter
#classB: ClassB
constructor() {
this.#classB = new ClassB()
}
methodA() {
'calls the class b method_b instead'
this.#classB.methodB()
}
}
// The Client
// Before the adapter I need to test the objects class to know which
// method to call.
const ITEMS = [new ClassA(), new ClassB()]
ITEMS.forEach((item) => {
if (item instanceof ClassB) {
item.methodB()
} else {
item.methodA()
}
})
// After creating an adapter for ClassB I can reuse the same method
// signature as ClassA (preferred)
const ADAPTED = [new ClassA(), new ClassBAdapter()]
ADAPTED.forEach((item) => {
item.methodA()
})
Output
node ./dist/adapter/adapter-concept.js
method A
method B
method A
method B
Adapter Use Case
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Example UML Diagram
Source Code
./src/adapter/client.ts
// Adapter Example Use Case
import CubeA from './cube-a'
import CubeBAdapter from './cube-b-adapter'
const totalCubes = 5
let counter = 0
const manufactureCube = () => {
// produce 5 cubes from which ever supplier can manufacture it first
const width = Math.floor(Math.random() * 10) + 1
const height = Math.floor(Math.random() * 10) + 1
const depth = Math.floor(Math.random() * 10) + 1
let cube = new CubeA()
let success = cube.manufacture(width, height, depth)
if (success) {
counter = counter + 1
} else {
// try other manufacturer
console.log('Company A was busy, so trying company B')
cube = new CubeBAdapter()
success = cube.manufacture(width, height, depth)
if (success) {
counter = counter + 1
} else {
console.log('Company B was busy, so trying company A')
}
}
}
// wait some time between manufacturing each cube
const interval = setInterval(() => {
manufactureCube()
if (counter >= totalCubes) {
clearInterval(interval)
console.log(`${totalCubes} cubes have been manufactured`)
}
}, 1000)
./src/adapter/cube-a.ts
// A hypothetical Cube tool from Company A
export interface ICubeA {
manufacture(width: number, height: number, depth: number): boolean
}
export default class CubeA implements ICubeA {
static last_time = Date.now()
manufacture(width: number, height: number, depth: number): boolean {
// if not busy, then manufacture a cube with dimensions
const now = Date.now()
if (now > CubeA.last_time + 1500) {
console.log(
`Company A built Cube with dimensions ${width}x${height}x${depth}`
)
CubeA.last_time = now
return true
}
return false // busy
}
}
./src/adapter/cube-b.ts
// A hypothetical Cube tool from Company B
export interface ICubeB {
create(
top_left_front: [number, number, number],
bottom_right_back: [number, number, number]
): boolean
}
export default class CubeB implements ICubeB {
static last_time = Date.now()
create(
top_left_front: [number, number, number],
bottom_right_back: [number, number, number]
): boolean {
// if not busy, then manufacture a cube with coords
const now = Date.now()
if (now > CubeB.last_time + 3000) {
console.log(
`Company B built Cube with coords [${top_left_front[0]},${top_left_front[1]},${top_left_front[2]}],[${bottom_right_back[0]},${bottom_right_back[1]},${bottom_right_back[2]}]`
)
CubeB.last_time = now
return true
} else {
return false // busy
}
}
}
./src/adapter/cube-b-adapter.ts
// Adapter for CubeB that implements ICubeA
import { ICubeA } from './cube-a'
import CubeB from './cube-b'
export default class CubeBAdapter implements ICubeA {
#cube: CubeB
constructor() {
this.#cube = new CubeB()
}
manufacture(width: number, height: number, depth: number): boolean {
const success = this.#cube.create(
[0 - width / 2, 0 - height / 2, 0 - depth / 2],
[0 + width / 2, 0 + height / 2, 0 + depth / 2]
)
return success
}
}
Output
node ./dist/adapter/client.js
Company A was busy, so trying company B
Company B was busy, so trying company A
Company A built Cube with dimensions 6x5x10
Company A was busy, so trying company B
Company B built Cube with coords [-4,-3,-2.5],[4,3,2.5]
Company A built Cube with dimensions 4x5x3
Company A was busy, so trying company B
Company B was busy, so trying company A
Company A built Cube with dimensions 10x2x1
Company A was busy, so trying company B
Company B built Cube with coords [-0.5,-2,-2.5],[0.5,2,2.5]
5 cubes have been manufactured
Summary
...Refer to Book or Videos for extra content.