java - 将数据导入二维公共(public)数组

Question

我正在为学校开发一个程序，它将 3 个程序组合在一起(一个转置二维数组，一个将对角线相加并告诉它们，一个将行相加)。我遇到的问题是将所有数据导入二维数组“输入”，以便所有方法都可以使用它。每次我尝试运行该程序时，它都会给出“java.lang.NullPointerException:null”。我该如何解决这个问题？

我的代码:

    import java.io.File;
    import java.io.FileNotFoundException;
    import java.util.Scanner;
    /**
     * This is program combines 3 programs in 1
     * 
     * @author (your name) 
     * @version (a version number or a date)
     */
    public class threeprogs
    {
// instance variables - replace the example below with your own
private int x;
public static int[][] input;
public static int[][] output;
/**
 * Runs All methods
 */
public  static void main(String[] args)
{
   //inputs info
    File file = new File("prog464a.dat");
    try { 
        Scanner scanner = new Scanner(file);
        while(scanner.hasNextInt())
        {
            for(int i = 0; i<5; i++)
            {
                for(int j = 0; j<5; j++)
                {
                    input[i][j] = scanner.nextInt();
                    output[i][j] = input[i][j];
                }   
            }
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
   int programs = 0;
   while(programs <3)
    {
        //make all programs execute here
        switch (programs)
        {
                case 0:  transpose();
                 break;
                 case 1:  AddDiag();
                 break;
                 case 2:  AddRowsandCol();
                 break;
                }
         //prints output
        for(int i=0; i<5;i++)
        {
            System.out.print("\n");
            for(int j=0;j<5;j++)
            {
                System.out.print(output[i][j]);
            }
        }
    }
}
/**
 * An example of a method - replace this comment with your own
 * 
 * @param  y   a sample parameter for a method
 * @return     the sum of x and y 
 */
public static int[][] transpose()
{  
    for(int i=0; i<input.length; i++)
    {
        for(int j=1; j<input[0].length; j++)
        {
            output[i][j] = input[j][i];
        }
    }
    return output;
}
public static String AddRowsandCol()
{  
    int total = 0;
    int loop = 0;
    for(int i=0; i<5; i++)
    {
       for(int j=0; j<5; j++)
       {
           if(loop<i)
           {
                output[loop][5] = total;
                total = 0;
           }
           total += output[i][j];
        }
    }
    return "Origional Matrix\n" +input +"\n\nWithTotals" +output;
}
public static String AddDiag()
{  
    int totala = 0;
    int totalb = 0;
    int count = 5;
    for(int i=0; i<5; i++)
    {
        count--;
        totala += input[i][i];
        totalb += input[i][count];
    }
    return "Main Diagonal Sum " +totala +"\nOther Diagonal Sum" +totalb;
}
    }

Answer 1

在分配任何值之前应初始化input数组

int[][] input = new int[5][5];

同样对于输出数组:

int[][] output = new int[5][5];