Java 错误消息 "Cannot be resolved to a variable"？

Question

好的，所以我对 java 有点陌生，我正在尝试创建一个类，它可以要求用户输入一个 12 位长的 upc 代码，检查以确保它是一个有效的代码，然后显示如果是或不是。我的当前程序有很多错误，我似乎无法弄清楚。这是我到目前为止的代码:

public class Upc {
    private long upc;

    public Upc(long upcs) {
        upc = upcs;
    }

    public long getUpc() {

        int m = (n2 + n4 + n6 + n8 + n10);
        long n = (n1 + n3 + n5 + n7 + n9 + n11);
        long r = (10 - (m + 3 * n) % 10);

        long n12 = (int) (upc % 10);
        upc /= 10;
        long n11 = (int) (upc % 10);
        upc /= 10;
        long n10 = (int) (upc % 10);
        upc /= 10;
        long n9 = (int) (upc % 10);
        upc /= 10;
        long n8 = (int) (upc % 10);
        upc /= 10;
        long n7 = (int) (upc % 10);
        upc /= 10;
        long n6 = (int) (upc % 10);
        upc /= 10;
        long n5 = (int) (upc % 10);
        upc /= 10;
        long n4 = (int) (upc % 10);
        upc /= 10;
        long n3 = (int) (upc % 10);
        upc /= 10;
        long n2 = (int) (upc % 10);
        upc /= 10;
        long n1 = (int) (upc % 10);

        if (r == n12) {
            return (upc + " is a feasible UPC code");
        } else {
            return (upc + " is an invalid UPC code");
        }
    }
}

我的错误如下:

13 errors found:
File: C:\Users\Andrew\Downloads\Upc.java  [line: 10]
Error: n2 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 10]
Error: n4 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 10]
Error: n6 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 10]
Error: n8 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 10]
Error: n10 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 11]
Error: n1 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 11]
Error: n3 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 11]
Error: n5 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 11]
Error: n7 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 11]
Error: n9 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 11]
Error: n11 cannot be resolved to a variable
File: C:\Users\Andrew\Downloads\Upc.java  [line: 39]
Error: Type mismatch: cannot convert from java.lang.String to long
File: C:\Users\Andrew\Downloads\Upc.java  [line: 42]
Error: Type mismatch: cannot convert from java.lang.String to long

我觉得修复一两个问题可以消除很多问题，有人可以帮助我吗？

Answer 1

这个变量定义在

之后

long n12 = (int) (upc%10);
upc /= 10;
long n11 = (int) (upc%10);
upc /= 10;
long n10 = (int) (upc%10);
upc /= 10;
long n9 = (int) (upc%10);
upc /= 10;
long n8 = (int) (upc%10);
upc /= 10;
long n7 = (int) (upc%10);
upc /= 10;
long n6 = (int) (upc%10);
upc /= 10;
long n5 = (int) (upc%10);
upc /= 10;
long n4 = (int) (upc%10);
upc /= 10;
long n3 = (int) (upc%10);
upc /= 10;
long n2 = (int) (upc%10);
upc /= 10;
long n1 = (int) (upc%10);



int m = (n2 + n4 + n6 + n8 + n10);
long n = (n1 + n3 + n5 + n7 + n9 + n11);
long r = (10-(m+3*n)%10);

您正在使用 undefined variable ，使用后您定义了该变量

编辑:如果

当你定义你的方法与返回值一样长的时间并且你返回字符串值时，查看返回值

return (upc + " is a feasible UPC code"); 

你需要在方法中或作为返回时间更改返回类型，如果你想返回这个，那么你的方法签名看起来像这样

public long getUpc(){
  // and return will work
  return (upc + " is a feasible UPC code"); 
}

但是如果你只想要数值那么不要改变它的方法签名就像这样返回upc

return upc;