TypeScript 享元模式讲解和代码示例
享元是一种结构型设计模式， 它允许你在消耗少量内存的情况下支持大量对象。
模式通过共享多个对象的部分状态来实现上述功能。 换句话来说， 享元会将不同对象的相同数据进行缓存以节省内存。
复杂度：
流行度：
使用示例： 享元模式只有一个目的： 将内存消耗最小化。 如果你的程序没有遇到内存容量不足的问题， 则可以暂时忽略该模式。
识别方法： 享元可以通过构建方法来识别， 它会返回缓存对象而不是创建新的对象。
概念示例
本例说明了享元设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
index.ts: 概念示例
/**
* The Flyweight stores a common portion of the state (also called intrinsic
* state) that belongs to multiple real business entities. The Flyweight accepts
* the rest of the state (extrinsic state, unique for each entity) via its
* method parameters.
*/
class Flyweight {
private sharedState: any;
constructor(sharedState: any) {
this.sharedState = sharedState;
}
public operation(uniqueState): void {
const s = JSON.stringify(this.sharedState);
const u = JSON.stringify(uniqueState);
console.log(`Flyweight: Displaying shared (${s}) and unique (${u}) state.`);
}
}
/**
* The Flyweight Factory creates and manages the Flyweight objects. It ensures
* that flyweights are shared correctly. When the client requests a flyweight,
* the factory either returns an existing instance or creates a new one, if it
* doesn't exist yet.
*/
class FlyweightFactory {
private flyweights: {[key: string]: Flyweight} = <any>{};
constructor(initialFlyweights: string[][]) {
for (const state of initialFlyweights) {
this.flyweights[this.getKey(state)] = new Flyweight(state);
}
}
/**
* Returns a Flyweight's string hash for a given state.
*/
private getKey(state: string[]): string {
return state.join('_');
}
/**
* Returns an existing Flyweight with a given state or creates a new one.
*/
public getFlyweight(sharedState: string[]): Flyweight {
const key = this.getKey(sharedState);
if (!(key in this.flyweights)) {
console.log('FlyweightFactory: Can\'t find a flyweight, creating new one.');
this.flyweights[key] = new Flyweight(sharedState);
} else {
console.log('FlyweightFactory: Reusing existing flyweight.');
}
return this.flyweights[key];
}
public listFlyweights(): void {
const count = Object.keys(this.flyweights).length;
console.log(`\nFlyweightFactory: I have ${count} flyweights:`);
for (const key in this.flyweights) {
console.log(key);
}
}
}
/**
* The client code usually creates a bunch of pre-populated flyweights in the
* initialization stage of the application.
*/
const factory = new FlyweightFactory([
['Chevrolet', 'Camaro2018', 'pink'],
['Mercedes Benz', 'C300', 'black'],
['Mercedes Benz', 'C500', 'red'],
['BMW', 'M5', 'red'],
['BMW', 'X6', 'white'],
// ...
]);
factory.listFlyweights();
// ...
function addCarToPoliceDatabase(
ff: FlyweightFactory, plates: string, owner: string,
brand: string, model: string, color: string,
) {
console.log('\nClient: Adding a car to database.');
const flyweight = ff.getFlyweight([brand, model, color]);
// The client code either stores or calculates extrinsic state and passes it
// to the flyweight's methods.
flyweight.operation([plates, owner]);
}
addCarToPoliceDatabase(factory, 'CL234IR', 'James Doe', 'BMW', 'M5', 'red');
addCarToPoliceDatabase(factory, 'CL234IR', 'James Doe', 'BMW', 'X1', 'red');
factory.listFlyweights();
Output.txt: 执行结果
FlyweightFactory: I have 5 flyweights:
Chevrolet_Camaro2018_pink
Mercedes Benz_C300_black
Mercedes Benz_C500_red
BMW_M5_red
BMW_X6_white
Client: Adding a car to database.
FlyweightFactory: Reusing existing flyweight.
Flyweight: Displaying shared (["BMW","M5","red"]) and unique (["CL234IR","James Doe"]) state.
Client: Adding a car to database.
FlyweightFactory: Can't find a flyweight, creating new one.
Flyweight: Displaying shared (["BMW","X1","red"]) and unique (["CL234IR","James Doe"]) state.
FlyweightFactory: I have 6 flyweights:
Chevrolet_Camaro2018_pink
Mercedes Benz_C300_black
Mercedes Benz_C500_red
BMW_M5_red
BMW_X6_white
BMW_X1_red
