Company

BasicEmployee.java

package com.example.helloworld;

import java.util.Date;

/**
 * Created by wannabe on 18.04.15.
 */
public abstract class BasicEmployee {
    protected int id;
    protected String name;
    protected float salary;
    protected Date hiringDate;

    /**
     * @param id
     * @param name
     * @param salary
     * @param hiringDate
     */
    public BasicEmployee(int id, String name, float salary, Date hiringDate) {
        this.id = id;
        this.name = name;
        this.salary = salary;
        this.hiringDate = hiringDate;
    }

    public String name() {
        return this.name;
    }

    public float salary() {
        return this.salary;
    }

    public BasicEmployee salary(float salary) {
        this.salary = salary;
        return this;
    }

    public int id() {
        return this.id;
    }

    public Date hiringDate() {
        return this.hiringDate;
    }
}

Company.java

package com.example.helloworld;

import java.util.HashMap;

/**
 * Created by wannabe on 18.04.15.
 */
public class Company {
    protected HashMap<Integer, BasicEmployee> employees;
    protected String name;

    public Company(String name) {
        this.name = name;
        this.employees = new HashMap<>();
    }
    public Company(String name, HashMap<Integer, BasicEmployee> employees) {
        this.name = name;
        this.employees = employees;
    }
    public String name() {
        return this.name;
    }
    public HashMap<Integer, BasicEmployee> employees() {
        return this.employees;
    }
    public Company employees(HashMap<Integer, BasicEmployee> employees) {
        this.employees = employees;
        return this;
    }
    public Company addEmployee(BasicEmployee employee) {
        this.employees.put(employee.id(), employee);
        return this;
    }
}

Employee.java

package com.example.helloworld;

import java.util.Date;

/**
 * Created by wannabe on 18.04.15.
 */
public class Employee extends BasicEmployee {
    protected Head head;
    /**
     * @param id
     * @param name
     * @param salary
     * @param hiringDate
     */
    public Employee(int id, String name, float salary, Date hiringDate) {
        super(id, name, salary, hiringDate);
    }

    /**
     * @param id
     * @param name
     * @param salary
     * @param hiringDate
     * @param head
     */
    public Employee(int id, String name, float salary, Date hiringDate, Head head) {
        super(id, name, salary, hiringDate);
        this.head = head;
    }

    public Head head() {
        return this.head;
    }

    public BasicEmployee head(Head head) {
        this.head = head;
        return this;
    }
}

Head.java

package com.example.helloworld;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;

/**
 * Created by wannabe on 18.04.15.
 */
public class Head extends BasicEmployee {
    HashMap<Integer, BasicEmployee> subordinates;


    public static Head build(BasicEmployee employee) {
        return new Head(employee.id(), employee.name(), employee.salary(), employee.hiringDate());
    }
    public static Head build(BasicEmployee employee, HashMap<Integer, BasicEmployee> subordinates) {
        return new Head(employee.id(), employee.name(), employee.salary(), employee.hiringDate(), subordinates);
    }
    /**
     * @param id
     * @param name
     * @param salary
     * @param hiringDate
     */
    public Head(int id, String name, float salary, Date hiringDate, HashMap<Integer, BasicEmployee> subordinates) {
        super(id, name, salary, hiringDate);
        this.subordinates = subordinates;
    }

    /**
     * @param id
     * @param name
     * @param salary
     * @param hiringDate
     */
    public Head(int id, String name, float salary, Date hiringDate) {
        super(id, name, salary, hiringDate);
        this.subordinates = new HashMap<>();
    }

    public HashMap<Integer, BasicEmployee> subordinates() {
        return this.subordinates;
    }
    public Head subordinates(HashMap<Integer, BasicEmployee> subordinates) {
        this.subordinates = subordinates;
        return this;
    }
}

Main.java

package com.example.helloworld;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;

/**
 * Created by wannabe on 12.04.15.
 */
public class Main
{
    public static void main(String[] args) throws ParseException
    {
        Company company = new Company("Google");
        DateFormat formatter = new SimpleDateFormat("dd-MM-yyyy");

        Employee worker1 = new Employee(1, "Программист Вася", 15.55f, formatter.parse("11-11-2015"));
        HashMap<Integer, BasicEmployee> workerList = new HashMap<>();
        workerList.put(worker1.id(), worker1);

        Head head = new Head(2, "Сергей Брин", 500f, formatter.parse("11-11-2015"), workerList);

        company.addEmployee(worker1).addEmployee(head);
        for (Map.Entry<Integer, BasicEmployee> employee : company.employees().entrySet()) {
            System.out.println(employee.getValue().id());
        }
    }
}