12 - 상속 다루기 - 슈퍼클래스 추출하기

개요

비슷한 일을 수행하는 두 클래스가 보이면, 공통 부분을 추상화해 슈퍼클래스로 옮길 수 있다. 데이터는 필드 올리기, 동작은 메서드 올리기 리팩터링을 수행한다.

 

비슷한 대안으로 클래스 추출하기가 있다. 차이는 구성(과 위임)을 이용하냐 상속을 이용하냐 차이다.

 

예시

연간 비용, 월간 비용

class Employee{     constructor(name, id, monthlyCost){         this._id = id;         this._name = name;         this._monthlyCost = monthlyCost;     }     get monthlyCost() {return this._monthlyCost;}     get name() {return this._name;}     get id() {return this._id;}     get annualCost(){ return this._monthlyCost * 12; } } class Department{     constructor(name, staff){         this._name = name;         this._staff = staff;     }     get staff(){return this._staff.slice();}     get name(){return this._name;}     get totalMonthlyCost(){         return this.staff             .map(e=e.monthlyCost)             .reduce((sum,cost)=>sum+cost);     }     get headCount(){         return this.staff.length;     }     get totalAnnualCost(){         return this.totalMonthlyCost * 12;     } }

class Party{} //일단 빈 슈퍼클래스를 만들고 확장한다. class Employee extends Party{     constructor(name, id, monthlyCost){         super();         this._id = id;         this._name = name;         this._monthlyCost = monthlyCost;     }     get monthlyCost() {return this._monthlyCost;}     get name() {return this._name;}     get id() {return this._id;}     get annualCost(){ return this._monthlyCost * 12; } } class Department extends Party{     constructor(name, staff){         super();         this._name = name;         this._staff = staff;     }     get staff(){return this._staff.slice();}     get name(){return this._name;}     get totalMonthlyCost(){         return this.staff             .map(e=e.monthlyCost)             .reduce((sum,cost)=>sum+cost);     }     get headCount(){         return this.staff.length;     }     get totalAnnualCost(){         return this.totalMonthlyCost * 12;     } }

class Party{     constructor(name){//데이터부터 옮기기(생성자)         this._name = name;     } } class Employee extends Party{     constructor(name, id, monthlyCost){         super(name);         this._id = id;         this._monthlyCost = monthlyCost;     }     get monthlyCost() {return this._monthlyCost;}     get name() {return this._name;}     get id() {return this._id;}     get annualCost(){ return this._monthlyCost * 12; } } class Department extends Party{     constructor(name, staff){         super(name);         this._staff = staff;     }     get staff(){return this._staff.slice();}     get name(){return this._name;}     get totalMonthlyCost(){         return this.staff             .map(e=e.monthlyCost)             .reduce((sum,cost)=>sum+cost);     }     get headCount(){         return this.staff.length;     }     get totalAnnualCost(){         return this.totalMonthlyCost * 12;     } }

class Party{     constructor(name){         this._name = name;     }     //옮긴 데이터 관련 메서드 올리기     get name() {return this._name;} } class Employee extends Party{     constructor(name, id, monthlyCost){         super(name);         this._id = id;         this._monthlyCost = monthlyCost;     }     get monthlyCost() {return this._monthlyCost;}     get id() {return this._id;}     get annualCost(){ return this._monthlyCost * 12; } } class Department extends Party{     constructor(name, staff){         super(name);         this._staff = staff;     }     get staff(){return this._staff.slice();}     get totalMonthlyCost(){         return this.staff             .map(e=e.monthlyCost)             .reduce((sum,cost)=>sum+cost);     }     get headCount(){         return this.staff.length;     }     get totalAnnualCost(){         return this.totalMonthlyCost * 12;     } }

class Department extends Party{     constructor(name, staff){         super(name);         this._staff = staff;     }     get staff(){return this._staff.slice();}     //비슷한 로직은 좀 더 추상화된 쪽 이름으로, 혹은 추상화시켜 함수선언바꾸기     get monthlyCost(){         return this.staff             .map(e=e.monthlyCost)             .reduce((sum,cost)=>sum+cost);     }     get headCount(){         return this.staff.length;     }     get annualCost(){         return this.monthlyCost * 12;     } }

class Party{     constructor(name){         this._name = name;     }     get name() {return this._name;}     get annualCost(){         return this.monthlyCost * 12;     } } class Employee extends Party{     constructor(name, id, monthlyCost){         super(name);         this._id = id;         this._monthlyCost = monthlyCost;     }     get monthlyCost() {return this._monthlyCost;}     get id() {return this._id;} } class Department extends Party{     constructor(name, staff){         super(name);         this._staff = staff;     }     get staff(){return this._staff.slice();}     get monthlyCost(){         return this.staff             .map(e=e.monthlyCost)             .reduce((sum,cost)=>sum+cost);     }     get headCount(){         return this.staff.length;     } }