所以我创建一个包含单词的二叉搜索树。它需要一个文本文件并打印出单词和行号。但是我在代码中有一些空值，我不知道为什么。我已经发布了输出窗口以便向您显示，但我很困惑为什么它打印单词，行号然后为null。对于这个初学者来说，任何帮助都非常受欢迎！
public class WordTree {
public static String word;
//a set does not allow duplicates
public static Set<Integer> lineNumbers;
public static WordTree left;
public static WordTree right;
/** Constructs a tree consisting of a single node, with
* the given word and line number.
*
* @param w the word
* @param lineNo the line number
* @pre true
* @post word tree containing word w on line lineNo has been constructed
*/
public WordTree(String w, int lineNo) {
word = w;
lineNumbers = new TreeSet<Integer>();
lineNumbers.add(lineNo);
left = null;
right = null;
}
public static WordTree recordWord(WordTree tree, String word2, int lineNo) {
if (tree == null) {
tree = new WordTree(word, lineNo);
return tree;
}
else if (word.compareToIgnoreCase((String)(word2)) == 0) {
return tree; //duplicate word found - do nothing
}
else if (word.compareToIgnoreCase((String)(word2)) > 0){
if (left != null){
WordTree.left = recordWord(tree, word2, lineNo);
}
}
else if (word.compareToIgnoreCase(word2) < 0) {
if (right != null) {
WordTree.right = recordWord(tree, word2, lineNo);
}
}
return tree;
}
/**
* Displays all the words in a WordTree.
* @param right2
*
* @param tree the WordTree whose contents are to be displayed
* PRECONDITION: tree is a well formed binary search tree
* POSTCONDITION words have been written out in alphabetical order, each
* followed by ascending list of line numbers on which the word occurs
* @param lineNo
* @param s
* @return
* @return
*/
public static WordTree display(WordTree tree, String word, int lineNo) {
if (left != null) {
WordTree.display(tree, word, lineNo);
}
System.out.println(word + lineNumbers);
if (right != null) {
WordTree.display(tree, word, lineNo);
}
return tree;
}
/**
* Counts how many different words there are in a WordTree
*
* @param tree the WordTree whose words are to be counted
* @return the number of different words in tree
* PRECONDITION: tree is a well formed binary search tree
*/
public int numberOfEntries() {
int count = 1;
if (left != null) {
count += WordTree.left.numberOfEntries();
}
if (right != null) {
count += WordTree.right.numberOfEntries();
}
return count;
}
}
TreeUtils Class
public class TreeUtils {
public static WordTree tree;
public static String word2;
public static void main(String[] args){
WordTree wt = new WordTree(null, 0);
int lineNo = 1;
Scanner sc2 = null;
try {
sc2 = new Scanner(new File("C:/macavity.txt"));
} catch (FileNotFoundException e) {
e.printStackTrace();
}
while (sc2.hasNextLine()) {
Scanner s2 = new Scanner(sc2.nextLine());
while (s2.hasNext()) {
String s = s2.next();
if (s.contains("@")){
lineNo++;
}
else{
WordTree.recordWord(tree, word2, lineNo);
}
System.out.println(WordTree.display(tree, s, lineNo));
}
}
System.out.println("Count" + wt.numberOfEntries());
}
}
输出窗口
Macavity's[1]
null
a[1]
null
Mystery[1]
null
Cat:[1]
null
he's[1]
null
called[1]
null
the[1]
null
Hidden[1]
null
Paw[1]
null
@[1]
null
For[2]
null
he's[2]
null
the[2]
null
master[2]
null
criminal[2]
null
who[2]
null
can[2]
null
defy[2]
null
the[2]
null
Law.[2]
null
@[2]
null
He's[3]
null
the[3]
null
bafflement[3]
null
of[3]
null
Scotland[3]
null
Yard,[3]
null
the[3]
null
Flying[3]
null
Squad's[3]
null
despair[3]
null
@[3]
null
For[4]
null
when[4]
null
they[4]
null
reach[4]
null
the[4]
null
scene[4]
null
of[4]
null
crime[4]
null
Macavity's[4]
null
not[4]
null
there![4]
null
@[4]
null
[T.S.Eliot][5]
null
Count1
答案 0 :(得分：0)
而不是：
System.out.println(WordTree.display(tree, s, lineNo));
只是做：
WordTree.display(tree, s, lineNo);
当display返回一个WordTree对象时，如果没有更多节点要显示，它将最终成为null。并且您已经在display方法中打印了值，因此您无需打印WordTree对象。