问题描述
我目前正在编写一个程序，该程序创建学生并根据其自然顺序（姓，名，GPA和学生ID）将其存储在双链表中。 我只是从泛型及其工作原理开始，所以我有点迷茫。 我相信我的大部分代码都可以正常工作； 我唯一需要帮助的部分是将我的学生（具有多种数据类型）添加到我的双向链接列表类的main方法中的列表中。 任何帮助是极大的赞赏！ 这是我的学生，双链表和节点类，以及我正在从中读取的输入文件的片段以及每个学生的数据：
学生班：
public class Student{
long studentID;
String firstName;
String lastName;
float GPA;
public Student(String lastName, String firstName, float GPA, long studentID){
this.lastName = lastName;
this.firstName = firstName;
this.GPA = GPA;
this.studentID = studentID;
}
public int compareTo(Student s){
int result = this.lastName.compareTo(s.lastName);
if(result == 0){
result = this.firstName.compareTo(s.firstName);
if(result == 0){
result = Float.compare(this.GPA, s.GPA);
if(result == 0){
result = Long.compare(this.studentID, s.studentID);
}
}
}
return result;
}
public String toString(){
return this.lastName + ", " + this.firstName +
" GPA: " + this.GPA + " ID: " + this.studentID;
}
}
节点类：
public class Node<T>{
Node<T> previous;
Node<T> next;
Student data;
public Node(Student data){
this(data, null, null);
}
public Node(Student data, Node<T> previous, Node<T> next){
this.data = data;
this.previous = previous;
this.next = next;
}
}
双链表类：
import java.io.*;
import java.util.*;
import csci1140.*;
public class DoublyLinkedList<T> implements Iterable<Node>{
private Node root;
private Node tail;
private Node previous;
private class ListIterator implements Iterator<Node>{
Node current = root;
public boolean hasNext(){
return (current != null);
}
public Node next(){
Node answer;
answer = current;
current = current.next;
return answer;
}
}
public Iterator<Node> iterator(){
ListIterator listIterator = new ListIterator();
return listIterator;
}
public void add(T data){
Node<Student> newNode = new Node<Student>(data);
if(root == null){
root = newNode;
tail = root;
return;
}
Node current = root;
for( ; current!= null; current = current.next){
if(newNode.data.compareTo(current.data)<= 0){
break;
}
}
if(previous == null){
previous.next = newNode;
newNode.next = current;
if(current == null){
tail = newNode;
}
} else {
newNode.next = root;
root = newNode;
}
}
public static final void main(String[] args){
FileInputStream fileIn = null;
try{
fileIn = new FileInputStream("student_input.txt");
System.setIn(fileIn);
} catch(FileNotFoundException fnfe){
fnfe.printStackTrace(System.err);
}
//Do work here to create list of students
}
try{
fileIn.close();
} catch(Exception e){}
}
}
Student_input.txt：
1000
Lisa
Licata
2.28
1001
Shelley
Santoro
1.56
1002
Ok
Ota
3.33
1003
Cindi
Caggiano
1.65
1楼
仍不能完全确定，也许对此有所变化。
特别是这插入在第一个更大的Node之前，并且我仍然不确定这种情况下的泛型是什么，并且T需要是扩展Student的东西（很好，它需要compareTo方法）：
public void add(T data) {
for(Node<T> current = root; current != null; current = current.next) {
if (data.compareTo(current.data) <= 0) {
current = new Node<>(data,current.previous,current);
if(null == current.previous){
root = current;
}else {
current.previous.next = current;
}
if(null == current.next){
tail = current;
} else {
current.next.previous = current;
}
return;
}
}
tail = new Node<>(data,tail,null);
if(null == tail.previous) root=tail;
}
因此，您的列表应该看起来像这样（以确保T具有compareTo方法）：
public class DoublyLinkedList<T extends Student> implements Iterable<Node<T>> {
...
}
放在一起（最好像您一样将Node作为一个单独的文件-但为简便起见，我将其放入列表中）：
public class DoublyLinkedList<T extends Student> implements Iterable<Node<T>> {
public static class Node<S> {
Node<S> previous;
Node<S> next;
S data;
public Node(S data) {
this(data, null, null);
}
public Node(S data, Node<S> previous, Node<S> next) {
this.data = data;
this.previous = previous;
this.next = next;
}
}
private Node<T> root = null;
private Node<T> tail = null;
private class ListIterator implements Iterator<Node<T>> {
Node<T> current = root;
@Override
public boolean hasNext() {
return (current != null);
}
@Override
public Node<T> next() {
Node<T> answer;
answer = current;
current = current.next;
return answer;
}
}
@Override
public Iterator<Node<T>> iterator() {
ListIterator listIterator = new ListIterator();
return listIterator;
}
public void add(T data) {
for(Node<T> current = root; current != null; current = current.next) {
if (data.compareTo(current.data) <= 0) {
current = new Node<>(data,current.previous,current);
if(null == current.previous){
root = current;
}else {
current.previous.next = current;
}
if(null == current.next){
tail = current;
} else {
current.next.previous = current;
}
return;
}
}
tail = new Node<>(data,tail,null);
if(null == tail.previous) root=tail;
}
}