我正在编写一个程序，该程序具有一个二进制搜索树（Roster），Student对象通过它们的String Id插入。每个学生都有一个链接列表，其中添加了课程，其中包含课程的字符串和成绩。二叉搜索树是我自己的实现版本。
我无法实施我的方法来打印所有包含特定课程的学生。我认为我的printCourse方法中的实现是关闭的，因为我无法从我的Roster类下的displayStudent（）方法调用它。这是一项家庭作业，我已经实施了大部分其他方法，只是在努力解决这个问题，非常感谢任何帮助！
displayStudents（＆＃34; Math161＆＃34）;
是我正在努力实施的方法。它从我名册中的方法调用，我试图通过我的BST搜索
在我的BST中，方法printCourse（）应该检查每个学生链表，如果它包含上面列出的课程，并打印每个学生。这是我到目前为止所做的，这是不正确的：
> public void printCourse(Node n, String course) {
> if (n != null) {
> inOrder(n);
> if (n.element.getId().equals(course)) {
> System.out.print(n.element.getId() + " ");
> }
> }
> }
Homework5.class / Main：
public class Homework5 {
static Roster rost = new Roster();
public static void main(String[] args) {
addStudent();
displayAllStudents();
lookupStudent("11114");
addCourse();
displayStudents("Math161");
}
// add students to the roster
static void addStudent() {
rost.addStudent(new Student("11111", "Jon", "Benson"));
rost.addStudent(new Student("11112", "Erick", "Hooper"));
rost.addStudent(new Student("11113", "Sam", "Shultz"));
rost.addStudent(new Student("11114", "Trent", "Black"));
rost.addStudent(new Student("11115", "Michell", "Waters"));
rost.addStudent(new Student("11116", "Kevin", "Johnson"));
}
// display all students in the roster
static void displayAllStudents() {
rost.displayAllStudents();
}
// lookup a student in the roster
static void lookupStudent(String id) {
if (rost.find(id) != null) {
System.out.println(id + " found");
} else {
System.out.println(id + " not found");
}
}
// add courses to the roster
static void addCourse() {
rost.addCourse("11111", new Course("CS116", 80));
rost.addCourse("11111", new Course("Math161", 90));
rost.addCourse("11112", new Course("Math161", 70));
rost.addCourse("11112", new Course("CS146", 90));
rost.addCourse("11112", new Course("CS105", 85));
rost.addCourse("11113", new Course("CS216", 90));
rost.addCourse("11114", new Course("CIS255", 75));
rost.addCourse("11114", new Course("CS216", 80));
rost.addCourse("11114", new Course("Math161", 60));
rost.addCourse("11114", new Course("COMM105", 90));
}
// display students enrolled in a given course id
static void displayStudents(String courseId) {
rost.displayStudents(courseId);
}
}
Student.class：
class Student implements Comparable<Student> {
String id;
String firstName;
String lastName;
LinkedList<Course> courses = new LinkedList<>();
Student(String id, String fName, String lName) {
this.id = id;
this.firstName = fName;
this.lastName = lName;
}
public String getName() {
return lastName;
}
public void setName(String lName) {
this.lastName = lName;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
@Override
public int compareTo(Student other) {
return this.getId().compareTo(other.getId());
}
public void addCourse(Course course) {
courses.add(course);
}
}
Course.class：
class Course {
LinkedList<Course> course = new LinkedList<>();
String id; // course id
int grade;
Course(String id, int grade) {
this.id = id;
this.grade = grade;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public int getGrade() {
return grade;
}
public void setId(int grade) {
this.grade = grade;
}
}
Roster.class：
class Roster {
Student root;
int numStudents;
BST<Student> roster = new BST<>();
LinkedList<Course> courseList = new LinkedList<>();
public Roster() {
root = null;
numStudents = 0;
}
public void addStudent(Student st) {
roster.insert(st);
numStudents++;
}
public void displayAllStudents() {
roster.traverse(2);
}
public Student find(String id) {
return roster.find(id);
}
public void addCourse(String id, Course course) {
Student student = roster.find(id);
student.addCourse(course);
}
public void displayStudents(String courseId) {
roster.printCourse(courseId);
}
}
BST.java
class BST<Roster extends Comparable> {
private Node root;
public BST() {
root = null;
}
// Generic find method
public Student find(String id) {
Node current = root;
while (id.compareTo(current.element.getId()) != 0) {
if (id.compareTo(current.element.getId()) < 0) {
current = current.left;
}
else {
current = current.right;
}
if (current == null) {
return null;
}
}
return current.element;
}
public void insert(Student st) {
Node newNode = new Node(st);
if (root == null) {
root = newNode;
} else {
Node current = root;
Node parent = null;
while (true) {
parent = current;
if (st.getId().compareTo(current.element.getId()) < 0) {
current = current.left;
if (current == null) {
parent.left = newNode;
return;
}
} else {
current = current.right;
if (current == null) {
parent.right = newNode;
return;
}
}
}
}
}
public void printCourse(Node n, String course) {
if (n != null) {
inOrder(n);
if (n.element.getId().equals(course)) {
System.out.print(n.element.getId() + " ");
}
}
}
public void traverse(int traverseType) {
switch (traverseType) {
case 1:
System.out.print("\nPreorder traversal: ");
// call preOrder(root) and implement preOrder()
preOrder(root);
break;
case 2:
System.out.print("\nList of all students: ");
inOrder(root);
break;
case 3:
System.out.print("\nPostorder traversal: ");
// call postOrder(root) and implement postOrder()
postOrder(root);
break;
}
System.out.println();
}
private void inOrder(Node localRoot) {
if (localRoot != null) {
inOrder(localRoot.left);
System.out.print(localRoot.element.getId() + " ");
inOrder(localRoot.right);
}
}
private void preOrder(Node localRoot) {
if (localRoot != null) {
System.out.print(localRoot.element + " ");
preOrder(localRoot.left);
preOrder(localRoot.right);
}
}
private void postOrder(Node localRoot) {
if (localRoot != null) {
postOrder(localRoot.left);
postOrder(localRoot.right);
System.out.print(localRoot.element + " ");
}
}
}
class Node {
protected Student element;
protected Node left;
protected Node right;
public Node(Student st) {
element = st;
}
}
答案 0 :(得分：0)
我不知道这是否一切，但我认为看似错误的两件事是：
<Student>，但BST.java中BST的定义包含一个名单，而不是学生。注意：您无需使用＆lt;＆gt;内部类型除非该类型可以更改。如果BST只能应用于Student类型，那么在定义或创建BST时不需要它。另一方面，如果您的BST应该适用于任何类型的数据，您应该将BST定义为BST类<T extends Comparable>，并确保在类型应该去的地方使用T. （查看Google上的通用类型以获取更多示例。）