我正在开发一个关于电子数据处理系统的项目，由于上述类型的异常，我遇到了一些问题。在代码中我使用的是列表数组。我将在代码下方显示：
package panellinies;
import java.util.ArrayList;
import java.util.Scanner;
public class Panellinies
{
private static int i;
private static int j;
private static int k;
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
System.out.println("Give the number of candidates");
System.out.println();
int num_candidates = input.nextInt();
System.out.println();
System.out.println("Give the number of the universities");
int num_universities = input.nextInt();
System.out.println();
System.out.println("Give the number of lessons");
int num_lessons = input.nextInt();
System.out.println();
float[][] coefficients = new float [num_universities][num_lessons];
for (i = 0; i < num_universities; i++)
{
for (j = 0; j < num_lessons; j++)
{
System.out.println("Give the coefficients of each lesson for each university");
coefficients[i][j] = input.nextFloat();
}
}
float[][] grades = new float [num_candidates][num_lessons];
for (i = 0; i < num_candidates; i++)
{
for (j = 0; j < num_lessons; j++)
{
System.out.println("Give the grade of the candidate No. " + i+1 + " in lesson " + j+1);
do
{
grades[i][j] = input.nextFloat();
} while (grades[i][j] > 100 || grades[i][j] < 0);
}
}
int[] max_numberofcandidates = new int [num_universities];
for (i = 0; i < num_universities; i++)
{
System.out.println("Give the number of candidates that each university " + (i+1) + " accepts");
max_numberofcandidates[i] = input.nextInt();
}
int university_code = 0;
ArrayList<Integer>[] selected_universities = new ArrayList [num_candidates];
for (i = 0; i < num_candidates; i++)
{
try
{
selected_universities[i].add(0);
}
catch (NullPointerException e)
{
System.out.println("The exception: " + e + " has occured!");
}
}
int leaver = 0;
System.out.println("Breakpoint 1");
for (i = 0; i < num_candidates; i++)
{
System.out.println("Candidate No. " + i+1 + " give in sorted sequence the increasing codes of the universities you wish to enter...");
System.out.println("Press 0 to terminate your list");
do
{
try
{
if (leaver != 0) break;
System.out.println("Give your code now...");
university_code = input.nextInt();
selected_universities[i].add(university_code);
leaver++;
}
catch(NullPointerException e)
{
System.out.println("The exception: " + e + " has occured!");
}
} while (university_code != 0);
}
System.out.println("Breakpoint 2");
ArrayList<Integer>[] temporarily_success_candidates = new ArrayList [num_universities];
for (i = 0; i < num_universities; i++)
{
try
{
temporarily_success_candidates[i].add(0);
}
catch (NullPointerException e)
{
System.out.println("The exception: " + e + " has occured!");
}
}
float[][][] telikoi_vathmoi = new float [num_candidates][num_universities][num_lessons];
float[][] average_grades = new float [num_candidates][num_universities];
for (i = 0; i < num_candidates; i++)
{
for (j = 0; j < num_universities; j++)
{
average_grades[i][j] = 0;
for (k = 0; k < num_lessons; k++)
{
telikoi_vathmoi[i][j][k] = 0;
}
}
}
for (i = 0; i < num_candidates; i++)
{
for (j = 0; j < num_universities; j++)
{
telikoi_vathmoi[i][j][0] = 0;
for (k = 0; k < num_lessons; k++)
telikoi_vathmoi[i][j][k] += grades[i][k] * coefficients[j][k];
System.out.println("Breakpoint 3");
try
{
average_grades[i][j] = telikoi_vathmoi[i][j][k] / num_lessons;
}
catch (ArrayIndexOutOfBoundsException e)
{
System.out.println("The exception: " + e + " has occured!");
}
}
}
System.out.println("Breakpoint 4");
int highly_preferred_university;
try
{
for (i = 0; i < num_candidates; i++)
{
//while ((selected_universities[counter].get(0) != null) && (temporarily_success_candidates[counter].get(0) == null))
if ((selected_universities[i].get(0) != null) && (temporarily_success_candidates[i].get(0) == null))
{
try
{
highly_preferred_university = selected_universities[i].get(0);
if (temporarily_success_candidates[i].size() < max_numberofcandidates[i])
temporarily_success_candidates[i].add(i);
else
{
if (average_grades[i][highly_preferred_university] < average_grades[i - 1][highly_preferred_university])
System.out.println("Candidate No. " + (i + 1) + " you are rejected!");
else
{
for (j = i; j > 0; j--)
{
if (average_grades[j][highly_preferred_university] < average_grades[i][highly_preferred_university])
temporarily_success_candidates[highly_preferred_university].remove(j);
}
}
temporarily_success_candidates[i].add(i);
}
System.out.println("Breakpoint 5");
selected_universities[i].remove(highly_preferred_university);
}
catch (NullPointerException e)
{
System.out.println("The exception: " + e + " has occured!");
}
}
}
}
catch (NullPointerException e)
{
System.out.println("The exception: " + e + " has occured!");
}
System.out.println("Breakpoint 6");
for (i = 0; i < num_universities; i++)
{
try
{
System.out.println("The candidates having succeeded in entering the university with code: " + selected_universities[i] + " are the below ones: " + temporarily_success_candidates[i]);
}
catch (NullPointerException e)
{
System.out.println("The exception: " + e + " has occured!");
}
}
System.out.println("Breakpoint 7");
}
}
try-catch块指示ArrayIndexOutOfBoundsException和NullPointerException发生的位置。
如何解决这些问题，以免发生异常？
我期待尽快收到您的回复。
提前谢谢！
答案 0 :(得分：0)
目前尚不清楚你在这里要做什么：
//YOUR CODE
int university_code = 0;
ArrayList<Integer>[] selected_universities = new ArrayList[num_candidates];
for (i = 0; i < num_candidates; i++)
{
selected_universities[i] = null;
}
我认为你得到一个空指针异常，因为你没有初始化每个ArrayList。你只是将它设置为null。
尝试用以下内容替换空行：
selected_universities[i]= new ArrayList();
我很难说出你之后想要做什么，但是你可能需要在此之后调整（leave！= 0）代码。