Exception Handling in java

Question

i was trying to run the following code but i am getting error please clarify my doubt

import java.util.*;

    class Except 
    { public class AlfaException extends Exception{}
      public static void main(String[] args)
       {

        int b;
        Scanner s=new Scanner(System.in);
          try
            { 
              b=s.nextInt();
            }
          catch(InputMismatchException ex)
               {
                 try
                     {
                        if(('b'> 67)&&('b'<83)){}
                     }
                 catch(AlfaException e){
                   throw new AlfaException("hello");
                    }         
                 System.out.println("error found");
               }
        }
    }  



 Except.java:20: non-static variable this cannot be referenced from a static cont
ext
               throw new AlfaException("hello");
                     ^

1 error

@eng Because someone with a reputation lower than 2000 has already edited the question and the edit hasn't been approved by users with a higher reputation. — Ocaso Protal
– Ocaso Protal, Commented Jul 19, 2011 at 6:53
Alternatively, you can throw the exception as follows: new Except().new AlphaException();. — Buhake Sindi
– Buhake Sindi, Commented Jul 19, 2011 at 6:55

bezmax · Accepted Answer · 2011-07-19 06:39:44Z

5

Static context is a context that runs on class without actual instance of that class. Your main method is static, that means it can only access static variables. However, your AlfaException is not static. Meaning that it will be bound to an instance of Except class - which you do not have.

Therefore you have 2 choises:

Make AlfaException also static: public static class AlfaException extends Exception{}. That will make it reside in static scope so it will be possible to access it from static functions.
Move all the main(...) method logic into non-static context. Create a function called doWork() that is not static, move all the code from main to doWork, and then call it like this:

.

public static void main(String[] args) {
    Except instance = new Except();
    instance.doWork();
}

answered Jul 19, 2011 at 6:39

bezmax

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Comments

developmentalinsanity · Accepted Answer · 2011-07-19 06:34:57Z

3

Your AlfaException is a non-static inner class of Except, so it can only be instantiated from inside an instance of Except. The main method is static, so doesn't have an enclosing instance.

Change the declaration of AlfaException to:

public static class AlfaException extends Exception{}

and it should work.

answered Jul 19, 2011 at 6:34

developmentalinsanity

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fnst · Accepted Answer · 2011-07-19 06:46:28Z

0

There are couple of mistakes:

AlfaException is never thrown in your try-block
AlfaException is a non-static inner class of Except (see other answers)
If you rethrow AlfaException in catch-block, the main needs a throws like this:
```
public static void main(String[] args) throws AlfaException { ...
```

answered Jul 19, 2011 at 6:46

fnst

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deepakl.2000 · Accepted Answer · 2011-07-19 06:51:48Z

0

import java.util.*;

class Except 
{ public static class AlfaException extends Exception{

    public AlfaException(String string) {
        super();
    }
}
  public static void main(String[] args) throws AlfaException
   {

    int b;
    Scanner s=new Scanner(System.in);
      try
        { 
          System.out.println("Enter the value for b");
          b=s.nextInt();
          System.out.println("b value is "+b);
        }
      catch(InputMismatchException ex)
           {
             if(('b'> 67)&&('b'<83)){}         
             System.out.println("error found");
           }
    }
}

output:
Enter the value for b
80b
error found

answered Jul 19, 2011 at 6:51

deepakl.2000

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