我在一天中的大部分时间都查看了我的代码，我无法弄清楚为什么我的BST不会填充。我已经包含了下面的所有代码，但是，具体问题在于fetch方法在Will和Ted之外的所有情况下都返回null。当我为Will或Ted以外的任何列表调用fetch时，返回null。我不知道问题出在fetch还是findNode（）。
package binarysearchtree;
public class SearchTree
{ TreeNode root;
public Listing compare;
public int i = 1;
public SearchTree()
{ root = null;
}
public boolean insert(Listing newListing)
{ TreeNodeWrapper p = new TreeNodeWrapper();
TreeNodeWrapper c = new TreeNodeWrapper();
TreeNode n = new TreeNode();
compare = newListing;
if(n == null)// out of memory
return false;
else // insert the node
{ n.node = newListing.deepCopy(); // fill in the TreeNode's fields
n.lc = null;
n.rc = null;
if(root == null) // tree is empty
{ root = n; }
else
{ findNode(newListing.getKey(), p, c); // find the node's parent
if(newListing.getKey().compareTo(p.get().node.getKey()) < 0)
p.get().lc = n; // insert new node as a left child
else
p.get().rc = n; // insert new node as a right child
}
return true;
}
} // end insert method
public Listing fetch(String targetKey)
{ boolean found;
TreeNodeWrapper p = new TreeNodeWrapper();
TreeNodeWrapper c = new TreeNodeWrapper();
found = findNode(targetKey, p, c); // locate the node
if(found == true)
return c.get().node.deepCopy();
else
return null;
} // end of fetch method
public boolean delete(String targetKey)
{ boolean found;
TreeNodeWrapper p = new TreeNodeWrapper();
TreeNodeWrapper c = new TreeNodeWrapper();
TreeNode largest;
TreeNode nextLargest;
found = findNode(targetKey, p, c);
if(found == false) // node not found
return false;
else // identify the case number
{ if(c.get().lc == null && c.get().rc == null) // case 1: deleted
// node has no
// children
{ if(p.get().lc == c.get()) // deleted node is a left child
p.get().lc = null;
else // deleted node is a right child
p.get().rc = null;
} // end case 1
else if(c.get().lc == null || c.get().rc == null) // case 2:
// 1 child
{ if(p.get().lc == c.get()) // deleted node is a left child
{ if(c.get().lc != null) // deleted node has a left child
p.get().lc = c.get().lc;
else
p.get().lc = c.get().rc;
}
else // deleted node is a right child
{ if(c.get().lc != null) // deleted node has a left child
p.get().rc = c.get().lc;
else
p.get().rc = c.get().rc;
}
} // end case 2
else // case 3: deleted node has two children
{ nextLargest = c.get().lc;
largest = nextLargest.rc;
if(largest != null) // left child has a right subtree
{ while(largest.rc != null) // move down right subtree
{ nextLargest = largest;
largest = largest.rc;
}
c.get().node = largest.node; // overwrite deleted node
nextLargest.rc = largest.lc; // save the left subtree
}
else // left child does not have a right subtree
{ nextLargest.rc = c.get().rc; // save the right subtree
if(p.get().lc == c.get()) // deleted node is a left child
p.get().lc = nextLargest; // jump around deleted node
else // deleted node is a right child
p.get().rc = nextLargest; // jump around deleted node
}
} // end of case 3
return true;
}
} // end of delete method
public boolean update(String targetKey, Listing newListing)
{ if(delete(targetKey) == false)
return false;
else if(insert(newListing) == false)
return false;
return true;
} // end of update
public class TreeNode
{ private Listing node;
private TreeNode lc;
private TreeNode rc;
public TreeNode()
{
}
} // end of class TreeNode
private boolean findNode(String targetKey, TreeNodeWrapper parent,
TreeNodeWrapper child)
{ parent.set(root);
child.set(root);
if(root == null) // tree is empty
return true;
while(child.get() != null)
{
if(child.get().node.compareTo(targetKey) == 0){ // node found
System.out.print("We finally found one!!!!!\n");
return true;
}
else
{ parent.set(child.get());
if(targetKey.compareTo(child.get().node.getKey()) > 0) {
System.out.print(child.get().node.getKey() + "\n");
child.set(child.get().lc);
}
else {
System.out.print(child.get().node.getKey() + "\n");
child.set(child.get().rc);
}
}
} // end while
return false;
} // end of findNode
public class TreeNodeWrapper
{ TreeNode treeRef = null;
public TreeNodeWrapper()
{
}
public TreeNode get()
{ return treeRef;
}
public void set(TreeNode t)
{ treeRef = t;
}
} // end of class TreeNodeWrapper
} // end class BinaryTree
班级＆＃34;列表＆＃34;
package binarysearchtree;
public class Listing
{ private String name; // key field
private String address;
private String number;
public Listing(String n, String a, String num)
{ name = n;
address = a;
number = num;
}
public String toString()
{ return("Name is " + name +
"\nAddress is " + address +
"\nNumber is " + number + "\n");
}
public Listing deepCopy()
{ Listing clone = new Listing(name, address, number);
return clone;
}
public int compareTo(String targetKey)
{ return(name.compareTo(targetKey));
}
public void setAddress(String a) // coded to demonstrate
// encapsulation
{ address = a;
} // end of setAddress method
public String getKey()
{
return name;
}
} // end of class Listing
最后是我的主要方法：
package binarysearchtree;
import binarysearchtree.BinaryTree.TreeNode;
public class BinarySearchTree {
public static void main(String[] args) {
SearchTree t = new SearchTree();
Listing l;
Listing l1 = new Listing("Ann", "1st Avenue", "111 1111");
Listing l2 = new Listing("Bill", "2nd Avenue", "222 2222");
Listing l3 = new Listing("Carol", "3rd Avenue", "333 3333");
Listing l4 = new Listing("Mike", "4th Avenue", "444 4444");
Listing l5 = new Listing("Pat", "5th Avenue", "555 5555");
Listing l6 = new Listing("Sally", "6th Avenue", "666 6666");
Listing l7 = new Listing("Ted", "7th Avenue", "777 7777");
Listing l8 = new Listing("Vick", "8th Avenue", "888 8888");
Listing l9 = new Listing("Will", "9th Avenue", "999 9999");
Listing l10 = new Listing("Zack", "11th Avenue", "101 0101");
Listing l11 = new Listing("Zeek", "12th Avenue", "121 2121");
//insert nodes
t.insert(l9);
t.insert(l7);
t.insert(l10);
t.insert(l2);
t.insert(l8);
t.insert(l1);
t.insert(l4);
t.insert(l3);
t.insert(l6);
t.insert(l5);
//fetch nodes
System.out.println(t.fetch("Carol"));
System.out.println(t.fetch("Sally"));
System.out.println(t.fetch("Ted"));
// delete nodes
t.delete("Carol"); // a node with NO children
System.out.println(t.fetch("Carol"));
t.delete("Sally"); // a node with ONE child
System.out.println(t.fetch("Sally"));
t.delete("Ted"); // a node with TWO children
System.out.println(t.fetch("Ted"));
// update nodes
t.update("Bill", l3);
System.out.println(t.fetch("Carol"));
System.out.println(t.fetch("Bill"));
System.out.print(l1.getKey());
System.exit(0);
}
}