如何在循环之外使用此变量？

Question

when i try to use the variable "encryptionKey" outside the loop or if-statement it's declared in, it throws a compile error "cannot find symbol".. any idea?

else if (inputPlainResultArray.length == 4 || inputPlainResultArray.length == 9 || inputPlainResultArray.length == 16)
{
   char[] encryptionKey = inputPlainResultArray;
   System.out.print("Encryption Key: ");
   System.out.print(encryptionKey);
   System.out.println();
   System.out.println();
   System.out.println();
   System.exit(0);

}
}
}

Answer 1

Because it's local variable , which means you can't access it outside the scope where it's declared. You should take a look on which types of variables exists in Java

In your particular case you may use instance variable , so you either declare char[] encryptionKey outside the method:

 public class YourClass{
   char[] encryptionKey;
   // other methods, fields, etc.
}

and you'll be able to use this variable in any place in this class, or declare inside the method, bit outside the else-if scope:

char[] encryptionKey = null;
if (...){}

else if (...){
char[] encryptionKey = inputPlainResultArray;
}

so it'll be visible for all entities inside this particular method.

Answer 2

That's because the scope of that variable is in the curly braces of the loop / if statement. You cannot use it like this. Instead declare it outside and use it.

In your case it will look something like this:

char[] encryptionKey = null;
if (...)
...
else if (inputPlainResultArray.length == 4 || inputPlainResultArray.length == 9 || inputPlainResultArray.length == 16)
{
    encryptionKey = inputPlainResultArray;
    System.out.print("Encryption Key: ");
    System.out.print(encryptionKey);
    System.out.println();
    System.out.println();
    System.out.println();
    System.exit(0);
}

Answer 3

create the variable outside of the method

char[] encryptionKey;

inside of the method then you can have

encryptionKey = ...

the only problem is if you try to call it before you initialize the variable, so be careful, or take precautions such as if(encryptionKey==null) return;

Answer 4

You cannot access the variable "encryptionKey" from outside the loop because you have declared it inside the loop. Move the declaration outside and it will work.

char[] encryptionKey;    
else if (inputPlainResultArray.length == 4 || inputPlainResultArray.length == 9 || inputPlainResultArray.length == 16)
{

             encryptionKey = inputPlainResultArray;
             ....
}

Answer 5

Use break keyword, not System.exit(0);

if(condition){
        //do something
        break;
    }