Chapter 13. Binary Search Tree
This chapter presents solutions to the previous exercise, then tests the performance of the tree-backed map. I present a problem with the implementation and explain how Java’s TreeMap
solves it.
A Simple MyTreeMap
In the previous exercise I gave you the outline of MyTreeMap
and asked you to fill in the missing methods. Now I’ll present a solution, starting with findNode
:
private Node findNode(Object target) { // some implementations can handle null as a key, but not this one if (target == null) { throw new IllegalArgumentException(); } // something to make the compiler happy @SuppressWarnings("unchecked") Comparable<? super K> k = (Comparable<? super K>) target; // the actual search Node node = root; while (node != null) { int cmp = k.compareTo(node.key); if (cmp < 0) node = node.left; else if (cmp > 0) node = node.right; else return node; } return null; }
findNode
is a private method used by containsKey
and get
; it is not part of the Map
interface. The parameter target
is the key we’re looking for. I explained the first part of this method in the previous exercise:
In this implementation,
null
is not a legal value for a key.Before we can invoke
compareTo
ontarget
, we have to typecast it to some kind ofComparable
. The type wildcard used here is as permissive as possible; that is, it works with any type that implementsComparable
and whosecompareTo
method acceptsK
or any supertype ofK
.
After all that, the actual search is relatively simple. We initialize ...
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