CODEWITHSUNDEEP
java
Rdesmond
Rdesmond

Reputation: 1211

Java: number of times something is initialized

I came across the code below, and was wondering if each Tree instance would be referencing a different EMPTY object, or if it would reference the same object for all tree instances (only be instantiated once).

class Tree<T> {
    public final Tree<T> EMPTY = new EmptyTree<T> ();

    /** True iff THIS is the empty tree. */
    public boolean isEmpty () { return false; }

    private static class EmptyTree<T> extends Tree<T> {
        /** The empty tree */
        private EmptyTree () { }
        public boolean isEmpty () { return true; }
    }
    ...
}

My intuition was that it would have to be 'public static final....' for only one object to be initialized across the class for EMPTY.

From page 99-100 of Data Structures Into Java

Upvotes: 1

Views: 74

Answers (1)

GhostCat
GhostCat

Reputation: 140525

You are correct. This code uses a new EMPTY object each time.

Which is of course valid, but not the "normal" thing to do. Of course, I am on of those people that say that static is actually an abnormality within good OO design; but the Java language allows to use static; and (unless there are good reasons within code not shown here) ... the reasonable way would be to have a shared static EMPTY Tree constant.

But that code looks strange anyway - what is the "sense" in having an isEmpty() method that returns always false for example?!

My "intuition" here: I would step back and do a full review of that code in order to understand if there are "more" surprises within that class.

Upvotes: 4

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