Book Excerpt and Interview: Effective Java, Second Edition

Josh,

We all love you and you are the star!!!!!

Thanks
Prashant

"They also asked us to add the following comment:"

which comment were you referring to ?

BR,
~A

My apologies - the comment being referred to is now found at the bottom of the article. When it was moved, the line you mentioned was not updated - it has been fixed now.

Thanks for catching that!

I'm very excited about this edition, and it is great to see InfoQ offering the generics chapter so we can take a peek before the book begins to ship. I don't know if this is the version that went to press, but I think there is a small error on a code snippet. On the bottom of page 121 we find:

// Reduction without generics or concurrency flaw
static Object reduce(List list, Function f, Object initVal) {
    Object[] snapshot = list.toArray(); // Locks list internally
    Object result = initVal;
    for (Object o : list)
        result = f.apply(result, o);
    return result;
}

// Reduction without generics or concurrency flaw
static Object reduce(List list, Function f, Object initVal) {
    Object[] snapshot = list.toArray(); // Locks list internally
    Object result = initVal;
    for (Object o : snapshot)
        result = f.apply(result, o);
    return result;
}

I am not sure I agree with your change entirely since the index of the array is never referenced in your code from within the for-each loop. However, I can see what you mean by the book version being incorrect since snapshot is not used anywhere.

Rafael,



You are absolutely right. What's worse, I caught this problem before the book went to print. I fixed it in the code example bundle (which will soon be posted on the book's web site). Somehow I failed to propagate the change into the book. I hope this is the only place where I did this.



I will fix the problem in the second printing and put it on the (currently nonexistent) errata page as soon as possible.



Thanks for spotting this!



Josh

Josh,

I'm wondering if you have revised Item 7 in the first edition, which contains this statement (in bold no less), which seems to me to be false:

"There is simply no way to extend an instantiable class and add an aspect while preserving the equals contract."

The example in the book missed these possible implementations for Point and ColorPoint respectively, which appear to me to fill the bill:

  public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null) return false;
    if (o.getClass() != getClass()) return false;
    Point p = (Point) o;
    return p.x == x && p.y == y;
  }

  public boolean equals(Object o) {
    if (!super.equals(o)) return false;
    ColorPoint p = (ColorPoint) o;
    return p.color == color;
  }

Very interesting & useful book. I really liked it

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