为什么我的 "plain1.findPosition(iMsg)" 会出现 NullPointerException？

Question

第一个 Class 给我错误。我要用字母 A-Z 创建一个数组，然后让用户输入它所需要的键，并将键数组中每个字符的位置与用户输入的字符串

的位置进行比较

import java.util.*;
    public class Encrypt{
        private Square plain1;
        private Square plain2;
        private Square Encrypt1;
        private Square Encrypt2;

    public Encryption(String key1, String key2) {
        Square plain1 = new Square();
        Square plain2 = new Square();
        Square Encrypt1= new Square(key1);
        Square Encrypt2= new Square(key2);
    } 


    public String encrypt(String msg) {
        String EmpS = "";
        String STR = "";

        for(int i = 0; i < message.length(); i+=2){
            char iMsg = message.charAt(i);
            char iMsg2 = message.charAt(i+1);
            int[] posRay = plain1.findPosition(iMsg);
            int[] posRay2 = plain2.findPosition(iMsg2);
            String answer = "" + Encrypt1.getChar(posRay[0], posRay2[1]);
            String Combined = "" + answer;
            String answer2 = "" + Encrypt2.getChar(posRay2[0], posRay[1]);
            String Combined2 = "" + answer2;

            String BothCom = Combined + Combined2;
            STR = STR.concat(BothCom);

        return STR;
        }
        return STR;
    }

负责数组的第2个class

public class Square {
    private char[][] matrix;
public Square() {
        arr= new char[5][5];
        int ascii= 65;
        for (int i = 0; i < 5; i++){
            for(int j = 0; j < 5; j++){
                arr[i][j] = (char) ascii;
                ascii++;
                }
            }
        }
}
public int[] findPosition(char Chart) {
        int[] position= new int[2];
        position[0] = -1;
        popositions[1] = -1;
        for (int i = 0; i < 5; i++){
            for (int j = 0; i < 5; j++){
                if(matrix[i][j] == Chart){
                posistion[0] = i;
                position[1] = j;
                return position;
                }
            }
        }

我发现这是一个错误（其他一切正常），有什么问题吗？：

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Square.getPos(char)" because "this.plain1" is null
        at findPosition.encrypt(Encrypt.java:45)
        at IO.printResults(IO.java:101)
        at Test.main(Proj8.java:26)

Answer 1

您不是在分配 class 变量，您实际上是在方法内部分配新的局部变量。更改为：

public Encryption(String key1, String key2) {
        plain1 = new Square();
        plain2 = new Square();
        Encrypt1= new Square(key1);
        Encrypt2= new Square(key2);
    }

为什么我的 "plain1.findPosition(iMsg)" 会出现 NullPointerException？

Why am I getting NullPointerException on my "plain1.findPosition(iMsg)"?

java

arrays

sorting

nullpointerexception