exception handling in instance initializer

[Tom Tang]

The following example is from Khalid book with little modification.

class RoomOccupancyTooHighException
      extends Exception {}                      // (1) Checked Exception
class BankrupcyException
      extends RuntimeException {}               // (2) Unchecked Exception
class Hotel {
    // Instance Members
    private static boolean BANKRUPT = true;
    private int NO_OF_ROOMS = 215;
    private int OCCUPANCY_PER_ROOM = 5;
    private int MAX_NO_OF_GUEST;
    {                                           // Instance initializer block
        //if (true)// (3)
            throw new BankrupcyException();     // (4) Throws unchecked exception
    }
    {                                           // (5) Instance block
        try {
             if (OCCUPANCY_PER_ROOM > 4)        // (6) Handles checked exception
                 throw new RoomOccupancyTooHighException();
        } catch (RoomOccupancyTooHighException e) {
             System.out.println("ROOM OCCUPANCY TOO HIGH: " + OCCUPANCY_PER_ROOM);
             OCCUPANCY_PER_ROOM = 4;
        }
        MAX_NO_OF_GUEST = NO_OF_ROOMS * OCCUPANCY_PER_ROOM;
    }
    // ...
}
public class ExceptionsInInstBlocks {
    public static void main(String args[]) {
        new Hotel();
    }
}

My question is if we comment out line3 like above, then we have a compiler error:
C:\WINDOWS\Desktop\pgjc-source\Example_8.6\ExceptionsInInstBlocks.java:14: initializer must be able to complete normally
{ // Instance initializer block
The compiler said "initializer must be able to complete normally". This is obviously not true( just compile with line 3 and see what happens). I just find it interesting the if(true) line make such difference when compiling.
Another question: Khalid said: "Instance initializer blocks in anonymous classe can throw any exceptions". But I have trouble compiling the following code (also from his book with little modification):

import java.io.*;
class Base {
    protected int a;
    protected int b;
    void print() {
        System.out.println("a: " + a);
    }
}
class AnonClassMaker {
    Base creatAnon() {
        return new Base() {           // (1) Anonymous class
            {                         // (2) Instance initializer
                a = 5; b = 10;
                if(true)
                throw new IOException();
            }
            void print() {
                super.print();
                System.out.println("b: " + b);
            }
        };  // end anonymous class
    }
}
public class InstanceInitBlock {
    public static void main(String args[]) {
        new AnonClassMaker().creatAnon().print();
    }
}

I found nowhere to declare the caught exception. The only way out is use try and catch block. Then the exception handling in instance initializer in this case will be the same as in a static intializer. Why Khalid said the former has greater freedom?

[Tom Tang]

I think this is an interesting question and would welcome anybody to shed more light.
Tom

[Tom Tang]

I bring this up one more time. Though the posting is fairly long, but I assure you it's worth your time.

[Rekha Rao]

Just giving a shot at this one, not sure if it makes enough sense.
I think, you need to connect lot of things together here.
From JLS 8.6:
"It is a compile-time error if an instance initializer cannot complete normally "
From JLS: 14.20
"A break, continue, return, or throw statement cannot complete normally"

Hence the following code will give a compiler error ('initializer must be able to complete normally') .
class Test{
{
throw new TestException();
}
}
class TextException extends RuntimeException{
}

Also from JLS 14:20,
"HYPOTHETICAL: An if-then statement can complete normally iff at least one of the following is true:
The if-then statement is reachable and the condition expression is not a constant expression whose value is true.
The then-statement can complete normally
"
So, the following code compiles fine as, if-then statement is considered to complete normally (since if statement is reachable) and hence the instance initializer itself is considered to complete normally.
class Test{
{
if(true) // or if(false)
throw new TestException();
}
}
class TextException extends RuntimeException{
}

[Val Dra]

Declare the error in the constructor throws yourerror i think not sure.

[Tom Tang]

Thanks Rekha. That is a very good try. Sometimes we have to go really deep into JLS to sort things out.