Question #5 from Doug's Book

[Thomas Paul]

The code below will not compile. One line needs a single change to make it compile. What is the change required?
(Hint: This is not a simple syntax error like a missing semicolon. Don't try to play compiler. There is a more fundamental problem.)

import java.util.*;
public class ABC {
    Calendar c = setCalendar();
    public ABC() {} 
    
    Calendar setCalendar() throws Exception{
        Calendar rightNow = Calendar.getInstance();
        if (rightNow.get(Calendar.MONTH) == Calendar.AUGUST)
            throw new Exception("Don't run this in August");
        return rightNow;        
    }
}

[Alton Hernandez]

import java.util.*;
public class ABC {
   Calendar c = setCalendar();
   public ABC() [B] throws Exception {}[/B]
   Calendar setCalendar() throws Exception{
       Calendar rightNow = Calendar.getInstance();
       if (rightNow.get(Calendar.MONTH) == Calendar.AUGUST)
            throw new Exception("Don't run this in August");
       return rightNow;
  }
}

I believe the initialization of the instance variables & initializers are all 'lump' together with the code of the constructor to form the <init> method. So if any of those throws an exception, it must be declared in the constructor.
Is that correct?
[ August 13, 2003: Message edited by: Alton Hernandez ]

[Unni Kainila]

I guessed the same. Good excercise for my GC lesson!
[ August 13, 2003: Message edited by: Unni Kainila ]

[rani bedi]

c variable need to be initialized in the constructor which throws Exception

import java.util.*;
public class ABC
{
Calendar c; // = setCalendar();
    public ABC() throws Exception
    {
c = setCalendar();
}
    Calendar setCalendar() throws Exception
    {
        Calendar rightNow = Calendar.getInstance();
        if (rightNow.get(Calendar.MONTH) == Calendar.AUGUST)
            throw new Exception("Don't run this in August");
        return rightNow;
    }
}

[Thomas Paul]

Alton has the correct answer. The rule is that if an instance variable initializer can throw an exception then every constructor must throw that exception. Good job!
Now go out an but a copy of JavaRules from amazon for less than $5!!!
[ August 14, 2003: Message edited by: Thomas Paul ]

[Maulin Vasavada]

hi Thomas
i knew the answer Alton wrote BUT i tried to confirm it using a program.
guess what? it didnt work for me so i didnt post my answer,
here is what i wrote and got,
Program:
-------
import java.util.*;
public class ABC {
Calendar c = setCalendar();
public ABC() throws Exception {}
Calendar setCalendar() throws Exception{
Calendar rightNow = Calendar.getInstance();
if (rightNow.get(Calendar.MONTH) == Calendar.AUGUST)
throw new Exception("Don't run this in August");
return rightNow;
}
}

Result of javac:
----------------
ABC.java:5: Exception java.lang.Exception can't be thrown in initializer.
Calendar c = setCalendar();
^
1 error

then i realized why it would not work and wrote the code Prameet came up with later on. that code worked but u specified in the question that only one line needed to change to make the code compile successully and so i thought my answer is invalid
not that i want the book but just to make sure we know the correct answer.
regards
maulin

[Maulin Vasavada]

it may b 'coz of machine/jvm combination differences?
i 'm on,
SunOS machine 5.8 Generic_108528-10 sun4u sparc SUNW,Ultra-80
regards
maulin

[Thomas Paul]

The answer as given is the correct answer for J2SE 1.4.

[Maulin Vasavada]

hi Thomas
u r right. in j2se1.4 it works!!
i decompiled the class file and got following which is same as Prameet wrote
i used 'cavaj' decompiler

import java.util.Calendar;
public class ABC
{
    Calendar c;
    public ABC()
        throws Exception
    {
        c = setCalendar();
    }
    Calendar setCalendar()
        throws Exception
    {
        Calendar calendar = Calendar.getInstance();
        if(calendar.get(2) == 7)
        {
            throw new Exception("Don't run this in August");
        } else
        {
            return calendar;
        }
    }
}

regards
maulin

[Alton Hernandez]

Originally posted by Thomas Paul:

Now go out an but a copy of JavaRules from amazon for less than $5!!!

So how do you get it for $5? It says $50 in Amazon.
[ August 14, 2003: Message edited by: Alton Hernandez ]

[Jim Yingst]

Follow the link for "used & new".

[Thomas Paul]

I bought my copy from one of these guys and it was almost perfect condition. The only thing that was less than perfect was a stamp on the back saying that it couldn't be returned to the publisher.