danchisholm.net exam3 Question 6

[Dmitry Golynkin]

class ColorException extends Exception {}
class WhiteException extends ColorException {}
abstract class Color {
  abstract void m1() throws ColorException;
}
class White extends Color {
  void m1() throws WhiteException {throw new WhiteException();}
  public static void main (String[] args) {
    White white = new White();
    int a,b,c,d;
    a = b = c = 0;
    try {
      white.m1();
      a++;
    } catch (WhiteException e) {b++;}
    finally {c++;}
    System.out.print(a+","+b+","+c);
  }
}

Hi friends. It seems that must be an error because method variable d doesn't initialized, but the code compiles fine. WHY?
[Code tags added by Val]
[ August 19, 2002: Message edited by: Valentin Crettaz ]

[Valentin Crettaz]

Local variables are not required to be initialized as long as they are not used within the method's body. In this case, d is not used, and thus, the compiler doesn't need to complain.
For more information, please read JLS 14.4 Local Variable Declaration Statements

[Dmitry Golynkin]

thank you Guru

[Dmitry Golynkin]

code:
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Question 19
1. class Amber {
2. public static void main(String[] args) {
3. int[][] a = {{1,2},{'a'-'a','b'-'a','c''a'},{~0,2&3,1<<1}};
4. Object[] obj = (Object[])a.clone();
5. for(int i = 0;i<obj.length; i++) {
6. int[] ia = (int[])obj[i];
7. System.out.print(ia[i]);
8. }
9. }
10. }
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What {1,2} and {~0,2&3,1<<1} are doing in the array initialization? ARE they array members?
[ August 19, 2002: Message edited by: Dmitry Golynkin ]
[ August 19, 2002: Message edited by: Dmitry Golynkin ]

[Valentin Crettaz]

First off, you should start another discussion when posting a new question unrelated to the one already under discussion.
Let's rewrite this:

int[][] a = {
     {1,2},
     {'a'-'a','b'-'a','c'-'a'},
     {~0,2&3,1<<1}
};

As you can see, the array "a" is a bidimensional array containing integer primitives. The components of the array "a" are initialized by the expressions given in the array initializer (after the '=' sign). Thus, the array after initialization contains the following values:
row 1: 1,2
row 2: 0,1,2
row 3: -1,2,2
Concerning the last subarray:
~0 inverts all bits of 0, which yields -1
2&3, that is, 00000010 & 00000011 yields 2
1 << 1 yields 2
And by the way (Dan?), I think there is a typo in the array initializer (unless the cut and paste didn't work).
Second row, third component, 'c''a' should be something like 'c'-'a'.
[ August 19, 2002: Message edited by: Valentin Crettaz ]

[Dan Chisholm]

Originally posted by Valentin Crettaz:

And by the way (Dan?), I think there is a typo in the array initializer (unless the cut and paste didn't work).
[ August 19, 2002: Message edited by: Valentin Crettaz ]

It must have been a cut and paste problem, because the web page doesn't have the problem.

[Valentin Crettaz]

That's what I thought Dan Keep up the good work...