打印3D陣列

Question

我正在嘗試打印3D陣列。 這是我的代碼：

    public static void print(int [][][] array)
{
    for (int i=0; i<array.length; i++ )
    {
        for (int x=0; x<array[i].length;x++)
        {
            System.out.println();
            System.out.print("row "+ x);
            for (int j=0; j<array[i][x].length;j++)
            {
                    System.out.print (array[i][x][j]+ " ");
            }
        }
    }

我做錯什么了嗎？ 每次我打電話

 ThreeDRay.print(d3);

我收到此錯誤：

在ThreeDRayRunner.main（ThreeDRayRunner.java:54）的ThreeDRay.print（ThreeDRay.java:13）處的線程“ main”中的java.lang.NullPointerException異常

其余代碼如下：

    public static void main( String args[] )
{
Scanner keyboard = new Scanner(in);

    out.print("How many matrices do you wish to enter? :: ");
    int matCnt = keyboard.nextInt();

    //instantiate a ThreeDRay

    int[][][] d3= new int [matCnt][][];


    for (int x=0; x < d3.length ;++x){
          d3[x] = new int[0][0];

    for(int i = 0; i < matCnt; i++)
    {
        out.print("What is the size of matrix " + i + " : ");
        int size = keyboard.nextInt();

        int[][] mat = new int[size][size];
        out.println();


        for(int r=0; r<mat.length; r++)
        {
            for(int c=0; c<mat[r].length; c++)
            {
                out.print("Enter a value for spot " + r + " - " + c + " :: ");
               mat[r][c]=keyboard.nextInt();
            }
        }



    if (i==0 && i<matCnt)
    {
    for (int l=0; l<=matCnt; l++){
          out.println("\nThreeDRay before setting mat at spot "+l);



    }
    }


       ThreeDRay.print(d3);


       d3[i] = mat;


        out.println("\nThreeDRay after setting mat at spot "+i);

           ThreeDRay.print(d3);

我必須證明我如何填充矩陣

 //user inputs values for first matrix 

在添加之前：

數組[0] =

數組[1] =

數組[2] =

//添加用戶輸入

添加后：

數組[0] =行0 = [...]

  row 1 = [...] ... depending on user given size of the first matrix Array[1] = Array[2] = 

//詢問第二個矩陣的輸入

在添加之前

數組[0] =行0 = [...]

  row 1 = [...] ... depending on user given size of the first matrix Array[1] = Array[2] = 

添加后

數組[0] =行0 = [...]

  row 1 = [...] ... depending on user given size of the first matrix 

數組[1] =行0 = [...]

  row 1 = [...] ... depending on user given size of the first matrix 

數組[2] =

Answer 1

您需要在此for循環中關閉花括號：

    for (int x = 0; x < d3.length; ++x) {
        d3[x] = new int[0][0];
    }

如果沒有大括號，您的程序將僅初始化d3一個元素，而其余元素仍為null之后，將繼續進入下一個for循環，當您嘗試打印正在執行的整個d3時，將給出NullPointerException 。