java - 如何打印空的二维数组而不出现空指针异常

Question

我对 Java 比较陌生，对于一个学校项目，我需要打印一个 2D 数组。该项目的基础是使用值 null 打印它。但我无法将其放入 for 循环而不得到 java.lang.NullPointerException。有人可以帮忙吗？

private int ROWS;
private int COLUMNS;
private int WIDTH;

private String[][] sheet;
private String[][] values;
private int precision;

public SpreadSheet(int rows, int cols, int width, int precision) {
    this.ROWS = rows;
    this.COLUMNS = cols;
    /*this.WIDTH = width;
    this.precision = precision;*/
}

public void printSheet(){
    for (int i = 0; i < sheet.length; i++) {
        for (int j = 0; j < sheet[i].length; j++) {
            System.out.println(sheet);
        }
        System.out.println("\n");
    }
}

主要:

import java.util.Scanner;
public class DemoSpreadSheet {

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    SpreadSheet sh = new SpreadSheet(4, 6, 15, 2);
    sh.printSheet();
}

}

Answer 1

对 SpreadSheet 函数进行一些小更改:

public SpreadSheet(int rows;int cols;int width;int precision)
    {
      this.Sheet=new String[rows][cols];
      /*creates an array with 4 rows and 6  columns..(assuming this is what you wanted to do)*/
      }

您的打印表函数也存在错误:

System.out.println(Sheet); //illogical
 /*sheet does not print the content of the array Sheet*/

将其更改为:

System.out.println(Sheet[i][j]);
/*this will print null */