我已創建二進制搜索樹通過使用樹接口和遞歸(我知道使用節點類我可以實現相同)提供的方法添加和檢查元素是否在二進制搜索樹或不。二進制搜索樹Instantiaition
我面臨的問題是在實例化&顯示BST的元素。
這裏是我的代碼
樹接口:
package bst;
public interface Tree<D extends Comparable>{
public boolean isempty();
public int cardinality();
public boolean member(D elt);
public NonEmptyBst<D> add(D elt);
}
EmptyBst類:
package bst;
public class EmptyBst<D extends Comparable> implements Tree<D>{
public EmptyBst(){
D data=null;
}
@Override
public boolean isempty() {
// TODO Auto-generated method stub
return true;
}
@Override
public int cardinality() {
// TODO Auto-generated method stub
return 0;
}
@Override
public boolean member(D elt) {
// TODO Auto-generated method stub
return false;
}
@Override
public NonEmptyBst<D>add(D elt) {
// TODO Auto-generated method stub
return new NonEmptyBst<D>(elt);
}
}
NonEmptyBst類
package bst;
public class NonEmptyBst<D extends Comparable> implements Tree<D> {
D data;
D root;
Tree<D> left;
Tree <D>right;
public NonEmptyBst(D elt){
data=elt;
root=elt;
left=new EmptyBst<D>();
right=new EmptyBst<D>();
}
NonEmptyBst(){
D dataThis=this.data;
}
public NonEmptyBst(D elt,Tree<D>leftTree,Tree<D>rightTree){
data=elt;
left=leftTree;
right=rightTree;
}
@Override
public boolean isempty() {
// TODO Auto-generated method stub
return false;
}
@Override
public int cardinality() {
// TODO Auto-generated method stub
return 1+left.cardinality()+right.cardinality();
}
public boolean member(D elt) {
if (data == elt) {
return true;
} else {
if (elt.compareTo(data) < 0) {
return left.member(elt);
} else {
return right.member(elt);
}
}
}
public NonEmptyBst<D> add(D elt) {
if (data == elt) {
return this;
} else {
if (elt.compareTo(data) < 0) {
return new NonEmptyBst(data, left.add(elt), right);
} else {
return new NonEmptyBst(data, left, right.add(elt));
}
}
}
}
BinarySearchTree類
package bst;
import bst.Tree;
import bst.EmptyBst;
import bst.NonEmptyBst;
public class BinarySearchTree {
public static void main(String[] args) {
// TODO Auto-generated method stub
NonEmptyBst abcd=new NonEmptyBst("abc");
NonEmptyBst ab=new NonEmptyBst(67);
abcd.add("cry me a river");
abcd.add("geeehfvmfvf");
abcd.add("I'm Sexy and i know it");
abcd.add("zzzzsd");
abcd.add("zzzzsd");
abcd.add("zzzfdsf");
abcd.add("zzfedfrsd");
abcd.add("tgrgdzsd");
abcd.add("gtrgrtgtrgtrzzzzsd");
abcd.add("zzzzsd");
abcd.add("zdddzzzsd");
abcd.add("zzzzsd");
abcd.add("zzzzsd");
}
}
** 我如何在所有節點訪問的數據,然後打印出來?我現在面臨的具體問題是在獲得一個例外,即ClassCastException
當我訪問在「葉節點」即使我在Initalize new NonEmptyBst<D>
我NonEmptyBst<D>(D elt)
constructor
我最終空指針異常
Exception in thread "main" java.lang.NullPointerException
at java.lang.String.compareTo(Unknown Source)
at java.lang.String.compareTo(Unknown Source)
at bst.NonEmptyBst.add(NonEmptyBst.java:51)
at bst.NonEmptyBst.add(NonEmptyBst.java:54)
at bst.BinarySearchTree.main(BinarySearchTree.java:11)
你在期待'D dataThis = this.data;'做什麼? 'this.data'在那一點爲空 –
我想創建一個'NonEmptyBst'的空實例來創建一個「指針」,通過它我可以迭代我的NonEmptyBst並將指針指向的數據當前「指向」的節點處的數據 –
異常在哪裏?請顯示堆棧跟蹤 –