从另一个类调用时如何保持输出变量

Question

In the main class the user inputs a number saved with the variable number but when I call a second class where the variable number is used it says it is unassigned.

Here the two classes:

Main class:

package maiN;

import java.util.Scanner;

public class director {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Scanner keyboard = new Scanner(System.in);
        System.out.println("enter a base nine number");

        String number = keyboard.next();
        nintodec.nintodec();

    }

}

and the called class where the variable number remains unassigned:

 package maiN;

 public class nintodec {
 public  static void nintodec(){
 number = new StringBuffer(number).reverse().toString();

 int numero=0 ;           
 int mult=1;
    for(int i = 0; i < number.length(); i++)
    {
       int digit = number.charAt(i);
       digit = Character.getNumericValue(digit);

        numero=numero+(mult*digit);

               mult=mult*9;
    }
    System.out.println(numero);

Answer 1

First off, change the method name nintodec() to convertToDec() so it won't be confused with a constructor.

public static void convertToDec() {...}

Now to your question. You can simply declare number as a parameter in the method.

public static void convertToDec(String number) {...}

When you call the method in the main class, pass in number as the argument. This gives convertToDec() access to the variable.

nintodec.convertToDec(number);

As a side note, class names should be in CamelCase . Change class director to Director , and class nintodec to NinToDec . Let me know if you need additional help.

Answer 2

So first of all you should stick to the naming conventions commonly used for Java applications (see Code Conventions for Java Programming Language ) also for the code snippets. So class names should be in CamelCase, package names all-lowercase, etc...

Regarding your question, the current code would not compile as the name number in the method ninetodec can not be resolved to a variable. This is because the variable "number" defined in the main method of class director is not visible outside of the method.

When calling

String number = Scanner.next();

a new local variable with the name "number" of type String is created within the scope of the main method. It contains the value returned by the call Scanner.next(). Only code within the same method block which is following this line, can read and interact with this variable.

It is not visible outside of this method, eg in the nintodec method, so the compiler complains that this variable is unknown. To make it visible for the nintodec method, I have to explicitly pass it to the method. So the following change of the code would at least compile

import java.util.Scanner;

public class director {

    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("enter a base nine number");

        String number = keyboard.next();
        nintodec.nintodec(number);
    }
}

and

public class nintodec {
    public static void nintodec(String number) {
        number = new StringBuffer(number).reverse().toString();

        int numero = 0;
        int mult = 1;
        for (int i = 0; i < number.length(); i++) {
            int digit = number.charAt(i);
            digit = Character.getNumericValue(digit);

            numero = numero + (mult * digit);

            mult = mult * 9;
        }
        System.out.println(numero);
    }
}