Published May 04, 2022
[
Every organization is composed of employees. Each of the employees has the same features i.e. has a salary, has some responsibilities, may or may not report to someone, may or may not have some subordinates etc.
Composite pattern lets clients treat the individual objects in a uniform manner.
In software engineering, the composite pattern is a partitioning design pattern. The composite pattern describes that a group of objects is to be treated in the same way as a single instance of an object. The intent of a composite is to “compose” objects into tree structures to represent part-whole hierarchies. Implementing the composite pattern lets clients treat individual objects and compositions uniformly.
Taking our employees example from above. Here we have different employee types
interface Employee {
getName(): string;
setSalary(salary: number);
getSalary(): number;
getRoles(): [];
}
class Developer implements Employee {
protected salary: number;
protected name: string;
protected roles;
constructor(name: string, salary: number) {
this.name = name;
this.salary = salary;
}
getName(): string {
return this.name;
}
getSalary(): number {
return this.salary;
}
getRoles(): [] {
return this.roles;
}
setSalary(salary: number) {
this.salary = salary;
}
}
class Designer implements Employee {
protected salary: number;
protected name: string;
protected roles;
constructor(name: string, salary: number) {
this.name = name;
this.salary = salary;
}
getName(): string {
return this.name;
}
getSalary(): number {
return this.salary;
}
getRoles(): [] {
return this.roles;
}
setSalary(salary: number) {
this.salary = salary;
}
}
Then we have an organization which consists of several different types of employees
class Organization {
protected employees: Employee[];
addEmployee(employee: Employee){
this.employees.push(employee);
}
getNetSalaries(): number {
return this.employees.reduce((salaries: number, employee: Employee) => {
return salaries + employee.getSalary()
}, 0)
}
}
And then it can be used as
const john = new Developer('John Doe', 12000)
const jane = new Developer('Jane Doe', 15000)
const organization = new Organization()
organization.addEmployee(john)
organization.addEmployee(jane)
organization.getNetSalaries();