Introduction

This assignment gives you opportunities to write a completely new generic entry tree class according to the following requirements. These requirements are selected to help you develop independent skills of writing methods for manipulating entry trees. Thus, you are provided with only a minimal set of template code. In addition, this assignment gives you opportunities to sharpen your testing skills with JUnit by writing JUnit test code for the entry tree class. Note that we have designed this assignment specially for this course, so some terms used in this assignment may be different from what other instructors have used before. Doing this assignment will help you develop the ability to understand trees and to write and debug well-structured programs.

An entry tree is a rooted tree with each node having any number of unordered children that are each given a unique key of type K. The root node is a dummy node with no key (key is null). Since the children of each node have different keys, a unique sequence of keys is obtained by walking down any path from the root to any other node and concatenating the keys at these nodes in order. So each path from the root to any other node corresponds to a unique sequence of keys. In addition to the key type K, there is another data type V called a value type. The root has no value (value is null), whereas every leaf node that is not the root has a value. Any internal node that is not the root either has a value or has no value. A pair of key sequence and value is called an entry. An entry tree is used to represent a mapping from key sequences to values with the property that if a node other than the root has a value, then the key sequence on the path from the root to the node is mapped to the value. Entry trees are useful as a data structure for representing a dictionary with the key type K being Character and the value type V being String and an Internet IP address directory in which each unique IP address as a sequence of Integer is assigned to an organization as a value.

An entry tree is implemented by using a linked structure (see a picture of an example entry tree in an attachment). In this structure, the children of a node are stored in a doubly linked list with no dummy node and not circular. Each node has a child link referring to the first node of the doubly linked list for its children. The child link of the node is null if it has no child. The nodes in the doubly linked list are connected together with links next and prev. The prev link of the first node in any doubly linked list is always null; the next link of the last node in any doubly linked list is always null. Each node has a parent link; the parent link of the root node is always null. The parent link of every child node refers to its parent node. In addition, each node has two types of data: key of type K and value of type V. The key and value fields of the root node are always null. Every other node has a key field that is not null. If a node has no value, then its value field is null. The value field of every leaf node that is not the root is never null.

You should first look at the attached input and output files before you read the specification of each method below in detail.

Requirements for class EntryTree

Write a public class named EntryTree with five public methods. The specification of each method is given below. You should introduce common private methods to avoid duplication of code. Note that a recursive method is easier to write than an iterative method. Both types of methods are acceptable for this assignment. We suggest that you first write the showTree method so that you can check if the tree constructed by other methods is correct by printing out the tree. In addition, you need to write a JUnit test set for each public method except showTree.

public V search(K[] keyarr)

The method returns null if keyarr is null or its length is 0. If any element of keyarr is null, then the method throws a NullPointerException exception. The method returns the value of the entry with the key sequence specified in keyarr or null if this tree contains no entry with the key sequence. An example is given in an attachment to illustrate this method.

public K[] prefix(K[] keyarr)

The method returns null if keyarr is null, or its length is 0. If any element of keyarr is null, then the method throws a NullPointerException exception. A prefix of the array keyarr is a key sequence in the subarray of keyarr from index 0 to any index m ΒΈ 0; the corresponding suffix is a key sequence in the subarray of keyarr from index m + 1 to index keyarr.length - 1. The method returns an array of type K[] with the longest prefix of the key sequence specified in keyarr such that the keys in the prefix are, respectively, with the nodes on the path from the root to a node. The length of the returned array is the length of the longest prefix. Note that if the length of the longest prefix is 0, then the method returns null. An example is given in the attachment to illustrate this method.

public boolean add(K[] keyarr, V aValue)

The method returns false if keyarr is null, its length is 0, or aValue is null. If any element of keyarr is null, then the method throws a NullPointerException exception. The method locates the node P corresponding to the longest prefix of the key sequence specified in keyarr such that the keys in the prefix label the nodes on the path from the root to the node. If the length of the prefix is equal to the length of keyarr, then the method places aValue at the node P and returns true. Otherwise, the method creates a new path of nodes (starting at a node S) labelled by the corresponding suffix for the prefix, connects the prefix path and suffix path together by making the node S a child of the node P, and returns true. An example is given in the attachment to illustrate this method.

public V remove(K[] keyarr)

The method returns null if keyarr is null or its length is 0. If any element of keyarr is null, then the method throws a NullPointerException exception. The method returns null if the tree contains no entry with the key sequence specified in keyarr. Otherwise, the method finds the path with the key sequence, saves the value field of the node at the end of the path, sets the value field to null. The following rules are used to decide whether the current node and higher nodes on the path need to be removed. The root node cannot be removed. Any node whose value is not null cannot be removed. Consider a non-root node whose value is null. If the node is a leaf node (has no child), then the node is removed. Otherwise, if the node is the parent of an only child and the child node is removed, then the node is removed. Finally, the method returns the saved old value.

public void showTree()

The method prints the tree on the console in the output format shown in the attachment. If the tree has no entry, then the method just prints out the line for the dummy root node.

Requirements for class Dictionary

Write a class named Dictionary with a main() method for using the EntryTree class to process a file of commands (one per line). Each command line consists of the name of a public method of the EntryTree class followed by its arguments in string form if the method has arguments. The name of the file is available to the main() method from its args argument at index 0. You can assume that the command file is correct in format. The main() method creates an object of the EntryTree class with K being Character and V being String, reads each line from the command file, decodes the line into String parts, forms corresponding arguments, and call the public method from the EntryTree object with the arguments, and prints out the result on the console. Note that the name of a public method in the EntryTree class on each command line specifies that the public method should be called from the EntryTree object. A sample input file of commands and a sample output file are attached.

The sample output file was produced by directing the console output to a file. The output from your program does not need to look exactly like the sample output file.

Requirements for inner class Node

The Node class needs to implement the EntryNode interface in a code template for automated testing.

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