代码编译但是当你运行它时会出现一条错误消息，它会给出一个空指针异常。作为SEEN的底部。代码应该从在程序中输入的txt文件中读取文本，然后创建一个新的txt文件，其中第一个txt文件的内容按服务年数排序。但是，我一直收到该错误消息。任何帮助将不胜感激。我在底部添加了错误消息，感谢所有帮助您的时间和精力的人，非常感谢：）
（25分）定义一个名为Employee的Java类。该类有数据成员 并为以下六个数据项中的每一个提供随附的访问器和增变器方法。 （这涉及创建Employee.java文件。）
服务年限（整数） （25分）创建一个包含至少五种不同数据的文本（数据）文件 员工（对象）。让每个数据项都在自己的行中 文本文件。例如，文件的前六行可能如下所示：
086244
莎莉·史密斯
100000.00
会计
管理器
7
（50分）'Heap'是一个满足堆属性的基于树的数据结构。 max-heap是一个完整的二叉树，其中每个内部节点中的值大于或等于该节点子节点中的值。
通过拥有一个堆（或一个满足堆属性的数组），在数组上执行重要任务会更有效（通常更快），例如在数组中查找最大元素（并删除它）和排序数组。
在此作业中，您必须编写一个程序，从文件中读取员工列表。该文件的名称将为“Employee.txt”。程序应将排序的数组输出到名为“SortedEmployee.txt”的文件中 Heapsort代码：
public class HeapSort
{
//heap sort method
public static <Employee extends Comparable<Employee>> void heapSort(Employee[] list)
{
//create a Heap of integers
Heap<Employee> heap = new Heap<>();
//add elements to the heap
for (int i = 0; i< list.length; i++)
heap.add(list[i]);
//remove elements from the heap
for(int i = list.length - 1; i >= 0; i--)
list[i] = heap.remove();
}
}
堆代码：
import java.util.ArrayList;
public class Heap<Employee extends Comparable<Employee>>
{
private ArrayList<Employee> list = new ArrayList<>();
public Heap(){}
public Heap(Employee[] objects)
{
for(int i = 0; i < objects.length; i++)
add(objects[i]);
}
public void add(Employee newObject)
{
list.add(newObject);
int currentIndex = list.size() - 1;
while(currentIndex > 0)
{
int parentIndex = (currentIndex -1)/2;
if(list.get(currentIndex).compareTo(list.get(parentIndex)) > 0)
{
Employee temp = list.get(currentIndex);
list.set(currentIndex, list.get(parentIndex));
list.set(parentIndex, temp);
}
else
break;
currentIndex = parentIndex;
}
}
public Employee remove()
{
if(list.size() == 0) return null;
Employee removeObject = list.get(0);
list.set(0, list.get(list.size() -1));
list.remove(list.size() -1);
int currentIndex = 0;
while(currentIndex < list.size())
{
int leftChildIndex = 2 * currentIndex + 1;
int rightChildIndex = 2 * currentIndex + 2;
if(leftChildIndex >= list.size()) break;
int maxIndex = leftChildIndex;
if(rightChildIndex < list.size())
{
if(list.get(maxIndex).compareTo(list.get(rightChildIndex)) < 0)
maxIndex = rightChildIndex;
}
if(list.get(currentIndex).compareTo(list.get(maxIndex)) < 0)
{
Employee temp = list.get(maxIndex);
list.set(maxIndex, list.get(currentIndex));
list.set(currentIndex, temp);
currentIndex = maxIndex;
}
else
break;
}
return removeObject;
}
public int getSize()
{
return list.size();
}
public void print()
{
for (int i = 0; i <= getSize()-1; i++)
{
System.out.print("Index: " + i + " Data: " + list.get(i));
System.out.println();
}
}
}
员工对象类：
public class Employee implements Comparable<Employee>
{
private String id;
private String name;
private double salary;
private String department;
private String position;
private int yos;
public Employee(String id, String name, double salary,String department,String position,int yos)
{
this.id = id;
this.name = name;
this.salary = salary;
this.department = department;
this.position = position;
this.yos = yos;
}
public void setid(String id)
{
this.id = id;
}
public void setname(String name)
{
this.name = name;
}
public void setsalary(double salary)
{
this.salary = salary;
}
public void setdepartment(String department)
{
this.department = department;
}
public void setposition(String position)
{
this.position = position;
}
public void setyos(int yos)
{
this.yos = yos;
}
public String getid()
{
return id;
}
public String getname()
{
return name;
}
public double getsalary()
{
return salary;
}
public String getdepartment()
{
return department;
}
public String getposition()
{
return position;
}
public int getyos()
{
return yos;
}
public int compareTo(Employee emp)
{
return (this.yos - emp.yos);
}
public String toString()
{
return "ID=" + this.id+ ", name=" + this.name+ ", salary= $" + this.salary+ ", department:" + this.department+ ", postion:" + this.position+ ",yos= $" + this.yos + "]\n";
}
}
演示代码：
import java.util.*;
import java.io.*;
public class EmployeeDemo
{
public static void main(String[] args)throws IOException
{
Employee[] list = new Employee[5];
Scanner keyboard = new Scanner(System.in);
System.out.println("Please enter the text file: ");
String fileName = keyboard.nextLine();
File myFile = new File(fileName);
Scanner inputFile = new Scanner(myFile);
//Read all of the values from the file
//and calculate their total
//Read a value from the file
String id = inputFile.nextLine();
String name = inputFile.nextLine();
double salary = inputFile.nextDouble();
String clear = inputFile.nextLine();
String department = inputFile.nextLine();
String position = inputFile.nextLine();
int yrService = inputFile.nextInt();
String llear = inputFile.nextLine();
list[0] = new Employee(id,name,salary,department,position,yrService);
//close the file
// File o = new File("SortedEmployee.txt");
//o.createNewFile();
System.out.println("Enter the file name to be transfered to: ");
String filename = keyboard.nextLine();
PrintWriter outputFile = new PrintWriter(filename);//dont need the top
//HeapSort<Employee> h = new heapSort<Employee>(Employee);
HeapSort.heapSort(list);
//Display the sum of the numbers
while(inputFile.hasNext())//this loop is wrong too
{
outputFile.println(list[0].toString());
}
outputFile.close();
inputFile.close();
System.out.print("File Sorted and Transferred");
}
}
这是我收到的错误消息：
Please enter the text file:
C:\Users\jose385\Desktop\Employee.txt
Enter the file name to be transfered to:
green
Exception in thread "main" java.lang.NullPointerException
at Heap.add(Heap.java:22)
at HeapSort.heapSort(HeapSort.java:13)
at EmployeeDemo.main(EmployeeDemo.java:50)
----jGRASP wedge2: exit code for process is 1.
----jGRASP: operation complete.
答案 0 :(得分：1)
您使Employee[] list = new Employee[5];
的大小为5
list[0] = new Employee(id,name,salary,department,position,yrService);
但只添加一个元素
Comparable实际上只对一个元素进行排序是什么意思
还尝试按照正确的方法来实施{{1}}