java - 将2d数组传递给构造函数时发生NullPointerException

当我尝试将2d数组（myString）传递给构造函数时，Eclipse在以下行中向我显示NullPointerException：

DenseBoard<String> temp1 = new DenseBoard<String>(myString, "a");

smb可以请我解释一下我做错了什么吗？提前致谢！

public class Tester {

    public static void main(String[] args){

        String[][] myString = {{"A B C"}, {"D E F"}, {"G H I"}};
        DenseBoard<String> temp1 = new DenseBoard<String>(myString, "a");
        System.out.println(temp1);
    }
}

类密集板

import java.util.*;
public class DenseBoard <T> {

 private ArrayList<ArrayList<T>> myBoard;

 public DenseBoard(T[][] x, T fillElem){

      for(int i = 0; i < x.length; i++){
         ArrayList<T> values = new ArrayList<T>();
          for(int j = 0; j < x[0].length; j++){
              values.add(x[i][j]);
          }
          myBoard.add(values);
      }
  }

 public String toString(){
      String result = "";
      for(int i = 0; i < myBoard.size(); i++){
          for(int j = 0; j < myBoard.get(i).size(); j++){
              result += myBoard.get(i).get(j);
          }
          System.out.println();
      }
      return result;
  }

}

最佳答案

您尚未初始化变量myBoard，并且在for循环中必须使用x[i].length而不是x[0].length

尝试这个：-

package p1;
import java.util.ArrayList;
public class A1{
    public static void main(String[] args) {
        String[][] myString = {{"A B C"}, {"D E F"}, {"G H I"}};
        DenseBoard<String> temp1 = new DenseBoard<String>(myString, "a");
        System.out.println(temp1);
    }
}

class DenseBoard <T> {
    private ArrayList<ArrayList<T>> myBoard;
    public DenseBoard(T[][] x, T fillElem){
        myBoard = new ArrayList<>();
        for(int i = 0; i < x.length; i++){
            ArrayList<T> values = new ArrayList<T>();
            for(int j = 0; j < x[i].length; j++){
                values.add(x[i][j]);
            }
            System.out.println(i);
            System.out.println(values);
            myBoard.add(values);
        }
    }
    public String toString(){
        String result = "";
        for(int i = 0; i < myBoard.size(); i++){
            for(int j = 0; j < myBoard.get(i).size(); j++){
                result += myBoard.get(i).get(j);
            }
            System.out.println();
        }
        return result;
    }
}

关于java - 将2d数组传递给构造函数时发生NullPointerException，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/32410081/