java - 为什么我的BST无法写入文件？

我正在尝试将我的BST写入文本文件，但是有些不起作用。我想知道我在哪里搞砸了，因为到目前为止，什么都没有写入文件中。问题出在BinaryTree.java中。我正在尝试将display()方法放入Student.txt文件中。

这是我的Node.java:

class Node  {
    Student data;
    Faculty data2;
    Node left;
    Node right;

    public Node(Student data) {
        this.data = data;
        this.left = left;
        this.right = left;
    }

    public Node(Faculty data2) {
        this.data2 = data2;
        this.left = left;
        this.right = right;
    }
}

这是我的BinaryTree.java:

int index = 0;
String[] sa = new String[index];

public void studentArray() {
    studentArray(root,index);
}

public int studentArray(Node root, int index) {
    if(root.left != null) {
        index = studentArray(root.left, index);
    }
    sa[++index] = root.data.getLastName().toString();
    if(root.right != null) {
        index = studentArray(root.right,index);
    }
    return index;
}

public void displayStudent(Node root) throws IOException {
    if(root != null) { // If root isn't empty.
        if(root.left != null) {
            displayStudent(root.left); // Recursively display left nodes.
        }
        System.out.println(root.data.toString()); // Print to the console data that's in the root in order.
        if(root.right != null) {
            displayStudent(root.right); // Recursively display right nodes.
        }
    }

    String file = "Student.txt";
    FileWriter fw = new FileWriter(new File(file));

    try {
        for(index = 0; index < sa.length; index++) {
            fw.write(sa[index] + " ");
        }
        fw.close();
    } catch(Exception e) {
        System.out.println("File not found.");
    }
}

这是我的Main.java:

import java.io.IOException;

public class Main {
    public static void main(String[] args) throws IOException {
        Student student1 = new Student("Mike", "Piazza", "S3123456");
        Student student2 = new Student("Jack", "Jill", "S3123456");
        Student student3 = new Student("Alice", "Jones", "S3123456");

        BinaryTree bt = new BinaryTree();
        bt.insertStudent(student1);
        bt.insertStudent(student2);
        bt.insertStudent(student3);
        bt.displayStudent(bt.root);
    }

这是我的Student.txt文件:

*displays nothing*

最佳答案

Java没有不断增长的数组，因此StudentArray将无法工作。

使用递归:

try (PrintWriter out = new PrintWriter(file, "UTF-8")) {
    print(out, root);
} // automatically closes out

void print(PrintWriter out, Node node) {
    if (node != null) {
        print(out, node.left);
        out.println(...);
        print(out, node.right);
    }
}

尝试使用资源很有用。
字符集UTF-8允许在学生姓名中进行任何签名。

替代数组，请使用ArrayList:

List<String> sa = new ArrayList<>();

sa.add(root.data.getLastName().toString();

for (int i = 0; i < sa.size(); ++i) { // Old-style, if you need the index i
    String s = sa.get(i);
    ...
    sa.set(i, s + s);
}

for (String s : sa) {
    System.out.println(s);
}