Java错误消息“无法解析为变量”？

Question

好吧，所以我有点新来的Java和我试图做一个类，这将能够要求用户输入一个12位长的upc代码，检查以确保其有效的代码，然后显示如果它是否。我目前的程序有很多错误，而且我似乎无法弄清楚。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"); 
     } 
    } 
} 

和是我的错误如下：

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 

我觉得像固定一两件事情将消除这种很多，谁能帮助我？

Answer 1

这个变量使用了不被定义的变量之后

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); 

找你定义和使用后，可以定义变量

编辑：因为如果

在定义你使用返回值的方法很长时间，并返回字符串值，请参阅返回值

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

您需要更改返回类型无论是在方法或回程时间一样，如果你想回到这点，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"); 
} 

，但如果你只想数值则没有变化它的方法签名只是像这样返回upc

return upc; 

Answer 2

这是因为你还没有宣布这些变量您在本使用它们这些行前：

int m = (n2 + n4 + n6 + n8 + n10); 
long n = (n1 + n3 + n5 + n7 + n9 + n11); 

您后宣布他们...基于我认为

你正在尝试做，你需要将这三条线移动到之后那大块的分割/模数码：

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

Answer 3

这是因为您在告诉编译器它们是什么之前使用了变量。首先，你应该宣布他们，然后使用它们。