要求有一个abstract类，类名为Employee。Employee的子类有YearWorker、MonthWorker、WeekWorker。YearWorker对象按年领取薪水，MonthWorker对象按年领取薪水，WeekWorker对象按年领取薪水。Employee有一个abstract方法。 子类必须重写父类的earnings()，给出各自领取薪水的具体方式。另外有一个Company类，该类用Employee对象数据成员，Employee对象数组的单元可以是YearWorker对象的上转型对象或MonthWorker对象的上转型对象或WeekWorker对象的上转型对象。程序能输出Company对象一年需要支付的薪水总额。

好的，以下是一个实现上述需求的Java代码：

abstract class Employee {
    public abstract double earnings();
}

class YearWorker extends Employee {
    private double salary;

    public YearWorker(double salary) {
        this.salary = salary;
    }

    @Override
    public double earnings() {
        return salary;
    }
}

class MonthWorker extends Employee {
    private double salary;

    public MonthWorker(double salary) {
        this.salary = salary;
    }

    @Override
    public double earnings() {
        return salary * 12;
    }
}

class WeekWorker extends Employee {
    private double salary;

    public WeekWorker(double salary) {
        this.salary = salary;
    }

    @Override
    public double earnings() {
        return salary * 52;
    }
}

class Company {
    private Employee[] employees;

    public Company(Employee[] employees) {
        this.employees = employees;
    }

    public double totalPay() {
        double total = 0;
        for (Employee e : employees) {
            total += e.earnings();
        }
        return total;
    }
}

public class Main {
    public static void main(String[] args) {
        Employee[] employees = new Employee[3];
        employees[0] = new YearWorker(50000);
        employees[1] = new MonthWorker(4000);
        employees[2] = new WeekWorker(800);
        Company company = new Company(employees);
        System.out.println("The company needs to pay " + company.totalPay() + " per year.");
    }
}

在这个程序中，Employee类是抽象类，定义了一个抽象方法earnings()。YearWorker、MonthWorker和WeekWorker类是Employee的子类，分别实现了earnings()方法来计算各自领取薪水的方式。

最后，Company类用Employee对象数据成员，Employee对象数组的单元可以是YearWorker对象的上转型对象或MonthWorker对象的上转型对象或WeekWorker对象的上转型对象。程序能输出Company对象一年需要支付的薪水总额。