java - 链接列表和 Try/Catch

Question

所以问题是:

Create a Employee class which cannot be instantiated and has the following      fields:

• String name;
• String ppsNumber;
• int employeeNumber;
• int numberOfEmployees;
• protected double pay;

These data members are tracked using appropriate setter and getter methods.  Hourly
employees are paid €15.00 per hour and commission based employees are paid  10% of the
value of their sales figure. In the class you are required to appropriately  plan for a earnings
method (double earnings() and ensure that the method must be implemented in  subclasses.

Create a HourlyEmployee class and a CommissionEmployee class that are derived from
Employee. In each of these classes, create an overridden method named earnings.

Finally, you are required to test your classes using a client class and to  store the instances of
employees into a LinkedList, using try/catch blocks where appropriate.

我已经完成了大部分工作，只是卡在了最后，我在其中的某个地方犯了一些错误，这里是:

public abstract class Employee {

    //private instances
    private String name;
    private String ppsNumber;
    private int employeeNumber;
    private int numberOfEmployees;
    protected double earnings;
    protected double pay;
    protected double sales;

//default constructor
public Employee(String name, String ppsNumber, int employeeNumber, int    numberOfEmployees, double earnings, double pay, double sales) {
    name = "Not Given";
    ppsNumber = "Not Givwn";
    employeeNumber = 0;
    numberOfEmployees = 0;
    earnings = 0;
    pay = 0;
    sales = 0;
}

//getters and setters
public String getName(){
    return name;
}   
public void setName(String name){
    this.name = name;
}

public String getPPSNumber(){
    return ppsNumber;
}   
public void setPPSNumber(String ppsNumber){
    this.ppsNumber = ppsNumber;
}

public int getEmployeeNumber(){
    return employeeNumber;
}   
public void setEmployeeNumber(int employeeNumber){
    this.employeeNumber = employeeNumber;
}

public int getNumberOfEmployees(){
    return numberOfEmployees;
}   
public void setNumberOfEmployees(int numberOfEmployees){
    this.numberOfEmployees = numberOfEmployees;
}

public double getPay(){
    return pay;
}   
public void setPay(double pay){
    this.pay = pay;
}

public double getEarnings(){
    return earnings;

}
public void setEarnings(double earnings){
    this.earnings = earnings;
}

public double getSales(){
    return sales;
}
public void setSales(double sales){
    this.sales = sales;
}

//calculateEarnings method
abstract double calculateEarnings();

//toString method
@Override
public String toString(){
    return name + ppsNumber + getEmployeeNumber();
}

}//end class

.

import java.util.Scanner;

public class HourlyEmployee extends Employee {
    public HourlyEmployee(){
        super();        
    }

    //constructor
    public HourlyEmployee(String name, String ppsNumber, int employeeNumber, int numberOfEmployees, double earnings, double pay){
        super(name, ppsNumber, employeeNumber, numberOfEmployees, earnings, pay,  pay);
    }

    //calculate earnings method
    @Override
    double calculateEarnings() {
        //input hours worked to calculate earnings
        Scanner input = new Scanner(System.in);
        System.out.println("Enter Hours Worked: ");
        pay = input.nextDouble();
        //calculate earnings
        earnings = pay * 15;
        System.out.println("Employee's Earnings: " + earnings);
        return earnings;

    }//end method
}//end class

.

import java.util.Scanner;

public class CommissionEmployee extends Employee {
    public CommissionEmployee(){
        super();
    }

    //constructor
    public CommissionEmployee(String name, String ppsNumber, int employeeNumber, int numberOfEmployees, double earnings, double sales){
        super(name, ppsNumber, employeeNumber, numberOfEmployees, earnings, sales, sales);
    }

    //calculate earnings methods
    @Override
    double calculateEarnings() {
        //input sales value to calculate earnings
        Scanner input = new Scanner(System.in);
        System.out.println("Enter Sales Value: ");
        sales = input.nextDouble();
        //calculate earnings
        earnings = sales * 0.1;
        System.out.println("Employee's Earnings: " + earnings);
        return earnings;

    }//end method
}//end class

.

import java.util.LinkedList;
import java.util.Scanner;
import java.util.List;
import java.lang.ArrayIndexOutOfBoundsException;
import java.util.InputMismatchException;

public class EmployeeTester {

     public static void main(String[] args){

            Scanner input = new Scanner(System.in);

            int numberOfEmployees = 0;

            while (numberOfEmployees == 0){
                try{
                   System.out.print("Enter Number of Employees: ");
                   numberOfEmployees = input.nextInt();
                } catch (InputMismatchException e) {
                    System.out.println("Exception Thrown " + e);
                } 
               input.nextLine();//clears input
            }//end while

            Employee[] employees = new Employee[numberOfEmployees];

            //create linked list
            List<Employee> employeeList = new LinkedList<Employee>();

            //declare & create an HourlyEmployee
            employeeList.add(new HourlyEmployee());

            for(int i=0; i<employees.length; i++){

                String name;
                String ppsNumber;
                int employeeNumber;
                int x = 0;

            System.out.print("Name: ");
            name = input.next();
            System.out.print("PPS Number: ");
            ppsNumber = input.next();
            System.out.print("Employee Number: ");
            employeeNumber = input.nextInt();     

            employeeList.get(x).setName(name);

            x++; //increment x


                try{//if not using length to control loop
                    employees[i].setName(name);
                    employees[i].setPPSNumber(ppsNumber);
                    employees[i].setEmployeeNumber(employeeNumber);
                } catch (ArrayIndexOutOfBoundsException e) {
                    System.out.println("Array Index Out of Bounds");
                }

            }//end for

            //enhanced for loop
            for(Employee element:employees){
                System.out.println(element.toString());
                System.out.println(element.calculateEarnings());
            } 


            //declare & create an CommissionEmployee
            employeeList.add(new CommissionEmployee());

            for(int i=0; i<employees.length; i++){

                String name;
                String ppsNumber;
                int employeeNumber;
                int x = 0;

            System.out.print("Name: ");
            name = input.next();
            System.out.print("PPS Number: ");
            ppsNumber = input.next();
            System.out.print("Employee Number: ");
            employeeNumber = input.nextInt();     

            employeeList.get(x).setName(name);

            x++; //increment x


                try{//if not using length to control loop
                    employees[i].setName(name);
                    employees[i].setPPSNumber(ppsNumber);
                    employees[i].setEmployeeNumber(employeeNumber);
                } catch (ArrayIndexOutOfBoundsException e) {
                    System.out.println("Array Index Out of Bounds");
                }

            }//end for

            //enhanced for loop
            for(Employee element:employees){
                System.out.println(element.toString());
                System.out.println(element.calculateEarnings());
            } 

        }//end main()
}//end class

所以最初我的问题是，当我运行代码时，它会询问有多少员工，并询问姓名、pps 号码和员工号码，然后我收到错误:

Exception in thread "main" java.lang.NullPointerException
at EmployeeTester.main(EmployeeTester.java:54)

然后我意识到我忘记添加小时雇员和佣金雇员的构造函数，所以我这样做了，现在父类(super class)出现了错误:

public class HourlyEmployee extends Employee {
public HourlyEmployee(){
    super();        
}

错误读取

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
The constructor Employee() is undefined

at HourlyEmployee.<init>(HourlyEmployee.java:5)
at EmployeeTester.main(EmployeeTester.java:31)

我仍然遇到第一个问题，如果有人可以帮助我修复它并让代码再次运行那就太好了，提前致谢

Answer 1

我注意到的一些问题(假设这是第 54 行):

try{//if not using length to control loop
                employees[i].setName(name);
                employees[i].setPPSNumber(ppsNumber);
                employees[i].setEmployeeNumber(employeeNumber);
            }

在此代码中，您假设存储在 employees 数组中的对象已初始化，但事实并非如此。你需要做这样的事情

try{//if not using length to control loop
                employees[i] = new HourlyEmployee(); //or some other employee.
                employees[i].setName(name);
                employees[i].setPPSNumber(ppsNumber);
                employees[i].setEmployeeNumber(employeeNumber);
            }

其次，这个错误:线程“main”java.lang.Error中的异常: Unresolved 编译问题:
构造函数 Employee() 未定义意味着Employee类没有无参数构造函数。在 Java 中，默认情况下每个对象都有一个无参数构造函数，但是当您提供自己的构造函数时，它将被删除。

因此，您需要在 Employee 类中创建一个新的无参数构造函数。

编辑:作为旁注，虽然展示您尝试过的内容很好，但在提出 future 问题时请不要提供所有代码，而应仅提供相关内容并补充一些显示问题的代码。