为什么我不能在文件中写入二进制树? [英] Why can't I write my binary tree inside a file?
问题描述
在我的BinaryTree.java文件中的displayStudent()方法中，我试图将我的带有学生的二叉树写入文件中.我的代码使我出错.我尝试了许多不同的方法来写入此文件，但均未成功，因此我为什么在这里.
Inside my displayStudent() method in my BinaryTree.java file, I'm trying to write my Binary Tree with students on them into a file. The code I have is throwing me an error. I've tried many different ways to write this file in with no success hence why I'm here.
这是我的Node.java文件:
class Node {
Student data;
Faculty data2;
Node left;
Node right;
public Node(Student data) {
this.data = data;
this.left = null;
right = null;
}
public Node(Faculty data2) {
this.data2 = data2;
this.left = null;
this.right = null;
}
}
这是我的BinaryTree.java文件:
import java.io.*;
public class BinaryTree {
public Node root; // Declaring Node that's a root.
public void insertFaculty(Faculty faculty) {
root = insertFaculty(faculty,root); // Let root equal faculty being inserted.
}
private Node insertFaculty(Faculty faculty, Node t) {
if(root == null) { // If the root is empty.
return new Node(faculty); // Return a faculty node.
}
// If inserted faculty last name is less than the current faculty last name
if(faculty.getLastName().compareTo(t.data2.getLastName()) < 0) {
if(t.left == null) { // If the left node is empty.
t.left = new Node(faculty); // Create a left a node that accepts a faculty name.
} else {
t.left = insertFaculty(faculty,t.left); // Insert faculty members to the left recursively.
}
return t; // Return node.
}
// If inserted faculty last name is less than the current faculty last name.
else if(faculty.getLastName().compareTo(t.data2.getLastName()) > 0) {
if(t.right == null) { // If the right node is empty.
t.right = new Node(faculty); // Create a right a node that accepts a faculty name.
} else {
t.right = insertFaculty(faculty,t.right); // Insert faculty members to the right recursively.
}
}
return t; // Return node.
}
public void insertStudent(Student s) {
root = insertStudent(s,root); // Let root equal student being inserted.
}
private Node insertStudent(Student s, Node t) {
if(root == null) { // If the root is empty.
return new Node(s); // Return a Student node.
}
// If inserted student last name is less than the current student last name.
if(s.getLastName().compareTo(t.data.getLastName()) < 0) {
if(t.left == null) { // If the left node is empty.
t.left = new Node(s); // Create a left a node that accepts a student name.
} else {
t.left = insertStudent(s,t.left); // Insert student members to the left recursively.
}
return t; // Return node;
}
// If inserted student last name is greater than the current student last name.
else if(s.getLastName().compareTo(t.data.getLastName()) > 0) {
if(t.right == null) { // If the right node is empty.
t.right = new Node(s); // Create a right a node that accepts a student name.
} else {
t.right = insertStudent(s,t.right); // Insert student members to the right recursively.
}
}
return t; // Return name.
}
public Node studentDelete(Student s, Node t) {
if(t != null) { // If t is empty.
// If inserted student last name is less than the current student last name.
if(s.getLastName().compareTo(t.data.getLastName()) < 0) {
t.left = studentDelete(s,t.left); // Left node will delete appropriate name recursively.
// If inserted student last name is greater than the current student last name.
} else if(s.getLastName().compareTo(t.data.getLastName()) > 0) {
t.right = studentDelete(s,t.right); // Right node will delete appropriate name recursively.
} else {
if(t.left == null) { // If left node is empty.
return t.right; // Return right node.
} else if(t.right == null) { // If right node is empty.
return t.left; // Return left node.
}
}
}
return t; // Return node.
}
public Node facultyDelete(Faculty faculty, Node t) {
if(t != null) { // If t is empty.
// If inserted faculty last name is less than the current faculty last name.
if(faculty.getLastName().compareTo(t.data2.getLastName()) < 0) {
t.left = facultyDelete(faculty,t.left); // Left node will delete appropriate name recursively.
// If inserted faculty last name is greater than the current faculty last name.
} else if(faculty.getLastName().compareTo(t.data2.getLastName()) > 0) {
t.right = facultyDelete(faculty,t.right); // Right node will delete appropriate name recursively.
} else {
if(t.left == null) { // If left node is empty.
return t.right; // Return right node.
} else if(t.right == null) { // If right node is empty.
return t.left; // Return left node.
}
}
}
return t; // Return node.
}
public void displayStudent(Node root) throws IOException {
if(root != null) { // If root isn't empty.
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.
displayStudent(root.right); // Recursively display right nodes.
}
String file = "Student.txt"; // Student text file, this will be used to write in student information.
FileWriter fw = null; // The file writer used to write in student information initially set to null.
try {
fw = new FileWriter(file, true); // Place file in FileWriter, true allows file to appended writer.
for(int i = 0; i < 30; i++) {
fw.write(root.data.toString());
}
fw.close(); // Close file.
} catch(FileNotFoundException e) { // Exception will be thrown if the file isn't found.
System.out.println("File not found!"); // Message will print if the file isn't found.
}
}
public void displayFaculty(Node root) {
if(root != null) { // If root isn't empty.
displayFaculty(root.left); // Recursively display left nodes.
System.out.println(root.data2.toString()); // Print to the console data that's in the root inorder.
displayFaculty(root.right); // Recursively display right nodes.
}
}
}
这是我的Main.java文件:
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:
null null null null null null null
这是我进入控制台的error:
Exception in thread "main" java.lang.NullPointerException
at BinaryTree.displayStudent(BinaryTree.java:118)
at BinaryTree.displayStudent(BinaryTree.java:107)
at BinaryTree.displayStudent(BinaryTree.java:107)
at Main.main(Main.java:13)
推荐答案
它显示"null null null null null null null null"的原因可以在displayStudent()方法中找到.您要显示displayStudent(root.right)，但要在构造函数中将这些节点设置为null.
The reason it prints "null null null null null null" can be found in your displayStudent() method. You're asking to displayStudent(root.right), but you're setting those nodes to null in the constructors.
public Node(Student data) {
this.data = data;
this.left = null;
right = null;
}
因此，当您显示这些数据时，您正在有效地运行displayStudent(null);
So when you go to display that data, you're running effectively displayStudent(null);
if(root != null) { // If root isn't empty.
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.
displayStudent(root.right); // Recursively display right nodes.
}
我认为您可以像这样解决此问题:
I think you can fix this like this:
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.
}
}
出现空指针异常的原因是，在调用fw.write(root.data.toString());
The reason you're getting a null pointer exception is that you are not checking for null values before you call fw.write(root.data.toString());
相反，我将使用StringBuilder将其添加到您一次写入文件的String中，而不是在每个对displayStudent()的调用中添加.我将其留给OP进行.
Instead, I'd use a StringBuilder to add to a String that you write to file once, instead of inside each of the calls to your displayStudent(). I leave that as an exercise to the OP.
随机建议:
拥有一棵既包含学生又包含您所学系的二叉树的某天可能会让您难过.我鼓励您在整个树中只使用一种数据类型(可能是学生和教职员工从某个抽象类扩展而来).
Random advice:
Having a binary tree that contains both Students and Faculty in the fashion you have is probably going to make you sad someday. I'd encourage you to have only one data type in the entire tree (possibly have Students and Faculty extend from some Abstract Class).
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