在 Java 中等待链表

Question

代码编译并运行，但addToEnd方法不起作用，这对我来说似乎是对的，但我不确定错误在哪里，有人可以指导我代码需要修复的内容或位置

这是我其他课程的代码

public class LinkedList {
private Node head;

/**
* constructor
* pre: none
* post: A linked list with a null item has been created.
*/
public LinkedList() {
head = null;
}
/** 
* Activity: finds size of the Linked List.
* Pre-Condition: none
* Post-Condition: The size of the list is returned
*/
public int size() {
int counter  = 0;
Node current = head;
while(current != null) {
counter++;
current = current.getNext();
}
return counter;   
}
/** 
* Adds a node to the end of the linked list.
* pre: String parameter
* post: The linked list has a new node at the end.
*/
public void addAtEnd(String s) {
Node current = head;
Node newNode = new Node(s);
if(head == null) {
head = newNode;
head.setNext(null);
} 
else {
while(current.getNext() == null) {
current.setNext(newNode);
current = newNode;
} 
}
}
private class Node {
private String data;
private Node next;

/**
* constructor
* pre: none
* post: A node has been created.
*/
public Node(String newData) {
data = newData;
next = null;
}

/**
* The node pointed to by next is returned
* pre: none
* post: A node has been returned.
*/
public Node getNext() {
return(next);
}

/**
* The node pointed to by next is changed to newNode
* pre: none
* post: next points to newNode.
*/
public void setNext(Node newNode) {
next = newNode;
}

/**
* The node pointed to by next is returned
* pre: none
* post: A node has been returned.
*/
public String getData() {
return(data);
}
}
}

这是我的主类代码，Blume 和 Dahl 永远不会被添加到列表中：

public class LinkedListDemo {
public static void main(String[] args) {
LinkedList list = new LinkedList();
list.addAtFront("Sachar");
list.addAtFront("Osborne");
list.addAtFront("Suess");
System.out.println("List has " + list.size() + " items.");
System.out.println(list);
list.addAtEnd("Blume");
list.addAtEnd("Dahl");
System.out.println(list);
}
}

Answer 1

public void addAtEnd(String s) {
Node current = head;
Node newNode = new Node(s);
if(head == null) {
head = newNode;
head.setNext(null);
} 
else {// problem is here. You need to find the  node that has getNext()==null, 
//so you need to loop all nodes where get next != null
while(current.getNext() == null) { 
current.setNext(newNode);
current = newNode;
} 
}

更改为此

else{ 
//iterate to the last node
while(current.getNext() != null) { 
current = current.getNext(); 
} 
//Append the new node to the end
current.setNext(newNode);  
}

Answer 2

while (current.getNext() == null) {
current.setNext(newNode);
current = newNode;
}

这是不正确的;因为你没有跟踪列表的尾部，你需要遍历整个列表，然后将newNode添加到末尾(我相信你已经理解了(。 为此，只需继续将current设置为current.getNext()，直到current.getNext()null，然后调用current.setNext(newNode);

Node next;
while ((next = current.getNext()) != null) {
current = next;
}
current.setNext(newNode);

Answer 3

public void addAtEnd(String s) {
Node current = head;
Node newNode = new Node(s);
if(current == null) {
head = newNode;
} else {
while(current.getNext() != null) {
current = current.getNext();
}
current.setNext(newNode); 
}
}