我试图实现一个包含给定节点的子节点列表的树。当我尝试在main方法中输出size时，它返回1。有人能看到我的createNode方法有什么问题吗?在有人生气之前，我只是包含了我所有的代码，这样你就可以看到我在做什么:)
public class LinkedTree<E> implements Tree<E> {
protected TreePosition<E> root; // reference to the root
protected int size; // number of nodes
public LinkedTree() {
root = null; // start with an empty tree
size = 0;
}
/** Returns the number of nodes in the tree. */
public int size() {
return size;
}
/** Returns whether the tree is empty. */
public boolean isEmpty() {
return (size == 0);
}
/** Returns whether a node is internal. */
public boolean isInternal(Position<E> v) throws InvalidPositionException {
return !isExternal(v);
}
/** Returns whether a node is external. */
public boolean isExternal(Position<E> v) throws InvalidPositionException {
TreePosition<E> vv = checkPosition(v); // auxiliary method
return (vv.getChildren() == null) || vv.getChildren().isEmpty();
}
/** Returns whether a node is the root. */
public boolean isRoot(Position<E> v) throws InvalidPositionException {
checkPosition(v);
return (v == root());
}
/** Returns the root of the tree. */
public Position<E> root() throws EmptyTreeException {
if (root == null)
throw new EmptyTreeException("The tree is empty");
return root;
}
/** Returns the parent of a node. */
public Position<E> parent(Position<E> v) throws InvalidPositionException,
BoundaryViolationException {
TreePosition<E> vv = checkPosition(v);
Position<E> parentPos = vv.getParent();
if (parentPos == null)
throw new BoundaryViolationException("No parent");
return parentPos;
}
/** Returns an iterable collection of the children of a node. */
public Iterable<Position<E>> children(Position<E> v)
throws InvalidPositionException {
TreePosition<E> vv = checkPosition(v);
if (isExternal(v))
throw new InvalidPositionException(
"External nodes have no children");
return vv.getChildren();
}
/** Returns an iterable collection of the tree nodes. */
public Iterable<Position<E>> positions() {
PositionList<Position<E>> positions = new NodePositionList<Position<E>>();
if (size != 0)
preorderPositions(root(), positions); // assign positions in
// preorder
return positions;
}
/** Returns an iterator of the elements stored at the nodes */
public Iterator<E> iterator() {
Iterable<Position<E>> positions = positions();
PositionList<E> elements = new NodePositionList<E>();
for (Position<E> pos : positions)
elements.addLast(pos.element());
return elements.iterator(); // An iterator of elements
}
/** Replaces the element at a node. */
public E replace(Position<E> v, E o) throws InvalidPositionException {
TreePosition<E> vv = checkPosition(v);
E temp = v.element();
vv.setElement(o);
return temp;
}
/** Adds a root node to an empty tree */
public Position<E> addRoot(E e) throws NonEmptyTreeException {
if (!isEmpty())
throw new NonEmptyTreeException("Tree already has a root");
size = 1;
root = createNode(e, null, null);
return root;
}
/** Swap the elements at two nodes */
public void swapElements(Position<E> v, Position<E> w)
throws InvalidPositionException {
TreePosition<E> vv = checkPosition(v);
TreePosition<E> ww = checkPosition(w);
E temp = w.element();
ww.setElement(v.element());
vv.setElement(temp);
}
/** If v is a good tree node, cast to TreePosition, else throw exception */
protected TreePosition<E> checkPosition(Position<E> v)
throws InvalidPositionException {
if (v == null || !(v instanceof TreePosition))
throw new InvalidPositionException("The position is invalid");
return (TreePosition<E>) v;
}
/** Creates a new tree node */
protected TreePosition<E> createNode(E element, TreePosition<E> parent,
PositionList<Position<E>> children) {
return new TreeNode<E>(element, parent, children);
}
/**
* Creates a list storing the the nodes in the subtree of a node, ordered
* according to the preorder traversal of the subtree.
*/
protected void preorderPositions(Position<E> v,
PositionList<Position<E>> pos) throws InvalidPositionException {
pos.addLast(v);
for (Position<E> w : children(v))
preorderPositions(w, pos); // recurse on each child
}
public Iterator<E> iteratorO() {
return null;
}
public boolean islnternal(Position<E> v) throws InvalidPositionException {
return false;
}
public static void main(String[] args) {
LinkedTree<Character> T = new LinkedTree();
// add root
T.addRoot('A');
// add children of root
T.createNode('B', (TreeNode) (T.root()), new NodePositionList());
TreePosition C = T.createNode('C', (TreeNode) (T.root()),
new NodePositionList());
T.createNode('D', (TreeNode) (T.root()), new NodePositionList());
// add children of node C
T.createNode('E', C, new NodePositionList());
TreePosition F = T.createNode('F', C, new NodePositionList());
T.createNode('G', C, new NodePositionList());
// add childrn of Node F
T.createNode('H', F, new NodePositionList());
T.createNode('I', F, new NodePositionList());
// print out tree
System.out.println("Size = " + T.size());
}
}
很简单。size的值设置不合理。只有两个地方需要进行写操作。
Line 4: protected int size; // number of nodes
Line 8: size = 0;
Line 12: public int size() {
Line 13: return size;
Line 18: return (size == 0);
Line 69: if (size != 0)
Line 97: size = 1;
Line 173: System.out.println("Size = " + T.size());
这是size()方法:
/** Returns the number of nodes in the tree. */
public int size() {
return size;
}
主要问题似乎是size本质上是多余的。但是，它阻止您解析整个树来确定元素计数，因此可以将其视为缓存。
正如您现在所经历的，缓存和其他冗余信息的一般问题是，您需要仔细跟踪它们并使它们保持最新。策略性地放置一些assert语句可以极大地帮助您完成这项任务。