Employee.java

public class Employee extends Person { //subclass of Person

	public Employee(String name, int salary) throws NegativeSalaryException {
		super(name, -salary);
		if (salary < 0) { //The salary given as argument is strictly less than 0
			throw new NegativeSalaryException("An employee cannot have a negative salary!");
		}
	}
	
	@Override
	public void pay(int amount) throws NegativeSalaryException {
      if (getDebt() + amount > 0) { //The argument is too positive and would change the employee's salary to become negative
          throw new NegativeSalaryException("An employee cannot be overpaid by " + (amount + getDebt()) + " yuans!");
      }
      setDebt(getDebt() + amount);
  }

	public static void testEmployee() {
		try {
			Employee e = new Employee("Daniel", -10000);
			System.out.println(false);
		} catch (NegativeSalaryException e) {
			System.out.println(e.getMessage() == "An employee cannot have a negative salary!");
		}
		try {
			Employee e = new Employee("Daniel", 0);
		} catch (NegativeSalaryException e) {
			System.out.println(false);
		}
		try {
			Employee e = new Employee("Daniel", 10000);
			System.out.println(e.getName() == "Daniel");
			System.out.println(e.getDebt() == -10000);
			e.setDebt(20000);
			System.out.println(e.getDebt() == 20000);
			e.setDebt(-10000);
			System.out.println(e.getDebt() == -10000);
			e.pay(2000);
			System.out.println(e.getDebt() == -8000);
			e.pay(-2000);
			System.out.println(e.getDebt() == -10000);
			e.pay(10000);
			System.out.println(e.getDebt() == 0);
			e.pay(1);
			System.out.println(false);
		} catch (NegativeSalaryException e) {
			System.out.println(e.getMessage().equals("An employee cannot be overpaid by 1 yuans!"));
		}
	}
}