594 Assignment 2: A Tree ADT
Spring 2006, David Matuszek
Implement general trees. Use Eclipse. Provide good Javadoc documentation for all public or package fields, constructors, and methods.
An abstract data type has a contract with its users, which is specified
by its public members and described via Javadoc. It provides certain operations,
and restricts access to only those operations. Your
is such an ADT.
In addition, any class is responsible for ensuring the validity of its data.
In this assignment, you are to take that responsibility very, very seriously
A tree is composed of nodes. Each node has a value, and may have
Tree class will be genericized, so that you
can specify the type of values in the nodes; the children will be (references
Your assignment is to define the following classes and methods.
public class Tree<V>
This is your ADT class. Each object in the
Tree class represents
a single node; however, nodes are linked together, so that any node may be considered
as the "root" of a complete tree. In the following, the terms "node"
and "Tree" are synonyms, but I tend to use "node" when I'm
talking about one specific object of type
Tree, and "Tree"
when I'm referring to that node and all its descendents (children, children
of children, etc.).
Tree class should have the following field:
public V value
public. Although a class is responsible for ensuring the validity of its members, it doesn't matter to us what the user does with this field, because it's just "data"--it doesn't affect the structure or validity of the tree.
Tree class should have the following constructor:
public Tree(V value, Tree... children)
- Creates a
Treenode with the given
valueand zero or more
Tree class should have the following methods:
public Tree firstChild()
public Tree lastChild()
public int numberOfChildren()
public Tree child(int index) throws NoSuchElementException
index-th child of this tree (counting from zero, as with arrays). Throws an
indexis less than zero or greater than or equal to the number of children.
public Iterator<Tree> children()
remove()methods, all of which should be implemented.
public void addChild(Tree newChild) throws IllegalArgumentException
newChildas the new last child of this tree, provided that the resultant tree is valid (see below). If the operation would result in an invalid tree, the tree is unchanged and the method throws an
public void addChild(int index, Tree newChild) throws IllegalArgumentException
newChildas the new
index-th child of this tree (counting from zero), provided that the resultant tree is valid (see below). The child previously at this index, and all subsequent children, are "shifted right" (their index is increased) to make room for the new child. If the index is less than zero or greater than (not greater than or equal to) the current number of children, or if the operation would result in an invalid tree, the tree is unchanged and the method throws an
public Tree removeChild(int index) throws NoSuchElementException
index-th child of this tree, or throws a
indexis illegal. (This method, and the
remove()method of the above Iterator, simply remove the child from the list of children of this tree; no major tree surgery is involved. The removed subtree remains intact.)
public boolean hasChildren()
trueif this node has children. This is a convenience routine: The user could just test
node.numberOfChildren() > 0instead.
public boolean equals(Object object)
Tree, and (2) the
valuefields of the two trees are equal, and (3) each child of one Tree
equalsthe corresponding child of the other Tree.
==, while non-null objects must be compared using
equals(Object), and (2) this method is recursive. Also note that you will need this method in order to do unit testing on your Tree class.
public String toString()
toString()representation of the value in that node, terminated with a newline (
\n). Each child is indented two spaces under its parent. For example:
one two five three four six seven
|The result of calling
"one\n two\n five\n three\n four\n six\n seven\n"
value. They are unnecessary because this is a public field and we don't care how it is used.
A tree will be considered valid if there are no loops in it. If, starting
from some node in the tree and following child links you can get back to the
same node, then there is a loop and the tree is invalid. You need to
test for validity in the
Child methods. We will,
however, allow subtrees to be shared, provided there are no loops.
Use the following algorithm. Before adding a node
child as a new
child of node
parent (each of which may be inside some tree structure),
test if node
child occurs in the tree whose root is
and test if node
parent occurs in the tree whose root is
If either of these conditions occurs, do not perform the operation,
but instead throw an
IllegalArgumentException instead. Note that
(1) the tests must search for identical (
==) nodes, not just equal
ones, and (2) the search is inherently recursive.
You will need a private search method to implement the tests.
Since this search method will be private, you cannot test it explicitly--rather,
you test it implicitly, by making sure that your
will throw an exception when asked to construct an invalid tree.
public class TreeTest
As part of the assignment, write, use, and turn in a JUnit test class for the
Tree class. Be thorough, and don't forget to test that exceptions
are thrown when they should be.
When grading your program, we will use our own JUnit tests, as well as or instead
of yours, so be sure to follow the above specifications exactly. Be especially
careful that your
toString() has the correct spaces and newlines.
The best way to keep the children of a node is probably in an
If a node has no children, your code will probably be simpler with an empty
ArrayList than with a
null value for children.
toString() methods, and the
search method you use to look for potential loops, must be recursive. You may
not use a
or similar data structure, to implement these methods.
Please use TDD (Test-Driven Development). This means:
Write stubs for all the methods. (Methods which return a value should
return the value that is most likely to be wrong.)
Doing things a little at a time this way is almost sure to reduce the amount of time you spend debugging.
Please zip up and turn in your completed program, including all Java source and class files and all Javadoc generated documentation, via Blackboard, before midnight Tuesday, January 24.