A Practical Introduction to Data Structures and Algorithm Analysis

Sec. 5.3 Binary Tree Node Implementations 165ABCDEFGHIFigure 5.8 Illustration of a typical pointer-based binary tree implementation,where each node stores two child pointers and a value.−∗c∗+4 x ∗a2xFigure 5.9 An expression tree for 4x(2x + a) − c.larger to handle the wider range of possible values. At the same time, leaf nodesneed not store child pointers.Java allows us to differentiate leaf from internal nodes through the use of classinheritance. As we have seen with lists and with class BinNode, a base classprovides a general definition for an object, and a subclass modifies a base class toadd more detail. A base class can be declared for nodes in general, with subclassesdefined for the internal and leaf nodes. The base class of Figure 5.10 is namedVarBinNode. It includes a virtual member function named isLeaf, which indicatesthe node type. Subclasses for the internal and leaf node types each implementisLeaf. Internal nodes store child pointers of the base class type; they do not distinguishtheir children’s actual subclass. Whenever a node is examined, its versionof isLeaf indicates the node’s subclass.