好的,所以我想学习如何打印链表。我有我需要用于列表的所有方法,但我无法弄清楚如何显示节点的值。现在我的main方法中没有任何内容,因为我在主要方法中尝试调用非静态方法时遇到错误。我有一个toString方法,显示列表的内容。我如何调用此toString来显示每个节点的值?任何建议将不胜感激。
这是节点类:
public class LinkedListNode
{
private int data;
private LinkedListNode next;
public LinkedListNode(int data)
{
this.data = data;
this.next = null;
}
public int getData()
{
return data;
}
public void setData(int d)
{
data = d;
}
public LinkedListNode getNext()
{
return next;
}
public void setNext(LinkedListNode n)
{
next = n;
}
}
这是LinkedList类,它包含操作列表的main和方法:
public class LinkedList {
public LinkedListNode head;
public static void main(String[] args) {
LinkedList l = new LinkedList();
l.insertFront(0);
System.out.println(l.toString());
}
public LinkedList() {
this.head = null;
}
public int removeFront(){
if(head == null){
System.out.println("Error - Attempting to call removeFront() on empty list");
return 0;
}else{
int temp = head.getData();
head = head.getNext();
return temp;
}
}
public void insertFront(int data){
if(head == null){
head = new LinkedListNode(data);
}else{
LinkedListNode newNode = new LinkedListNode(data);
newNode.setNext(head);
head = newNode;
}
}
public void insertBack(int data){
if(head == null){
head = new LinkedListNode(data);
}else{
LinkedListNode newNode = new LinkedListNode(data);
LinkedListNode current = head;
while(current.getNext() != null){
current = current.getNext();
}
current.setNext(newNode);
}
}
public int removeBack(){
if(head == null){
System.out.println("Error - Attempting to call removeBack() on empty list");
return 0;
}else if (head.getNext() == null){
int temp = head.getData();
head = null;
return temp;
}else{
LinkedListNode current = head;
while(current.getNext().getNext() != null){
current = current.getNext();
}
int temp = current.getNext().getData();
current.setNext(null);
return temp;
}
}
public String toString(){
String retStr = "Contents:\n";
LinkedListNode current = head;
while(current != null){
retStr += current.getData() + "\n";
current = current.getNext();
}
return retStr;
}
public LinkedListNode getHead() {
return head;
}
public void setHead(LinkedListNode head) {
this.head = head;
}
}
public static void main(String[] args) {
LinkedList list = new LinkedList();
list.insertFront(1);
list.insertFront(2);
list.insertFront(3);
System.out.println(list.toString());
}
String toString() {
String result = "";
LinkedListNode current = head;
while(current.getNext() != null){
result += current.getData();
if(current.getNext() != null){
result += ", ";
}
current = current.getNext();
}
return "List: " + result;
}
正如在其他一些答案和注释中所指出的,这里缺少的是调用JVM System类来打印由toString()方法生成的字符串。
LinkedList myLinkedList = new LinkedList();
System.out.println(myLinkedList.toString());
这将完成工作,但我不建议这样做。如果我们看一下Object类的javadocs,我们会找到toString()的这个描述:
返回对象的字符串表示形式。通常,toString方法返回一个“文本表示”此对象的字符串。结果应该是一个简洁但信息丰富的表示,便于人们阅读。建议所有子类都重写此方法。
这里强调的是我自己的。您正在创建一个包含链表的整个状态的字符串,有人使用您的类可能没有预料到。我建议进行以下更改:
在LinkedListNode中:
public String toString(){
return "LinkedListNode with data: " + getData();
}
在LinkedList中:
public int size(){
int currentSize = 0;
LinkedListNode current = head;
while(current != null){
currentSize = currentSize + 1;
current = current.getNext();
}
return currentSize;
}
public String toString(){
return "LinkedList with " + size() + "elements.";
}
public void printList(){
System.out.println("Contents of " + toString());
LinkedListNode current = head;
while(current != null){
System.out.println(current.toString());
current = current.getNext();
}
}
当JVM
尝试运行您的应用程序时,它会静态调用您的main方法;这样的事情:
LinkedList.main();
这意味着没有你的LinkedList
类的实例。为了调用你的toString()
方法,你可以创建一个LinkedList
类的新实例。
所以你的main
方法的主体应该是这样的:
public static void main(String[] args){
// creating an instance of LinkedList class
LinkedList ll = new LinkedList();
// adding some data to the list
ll.insertFront(1);
ll.insertFront(2);
ll.insertFront(3);
ll.insertBack(4);
System.out.println(ll.toString());
}
我这样做的方式如下:
public static void main(String[] args) {
LinkedList list = new LinkedList();
list.insertFront(1);
list.insertFront(2);
list.insertFront(3);
System.out.println(list.toString());
}
String toString() {
StringBuilder result = new StringBuilder();
for(Object item:this) {
result.append(item.toString());
result.append("\n"); //optional
}
return result.toString();
}
一个非常简单的解决方案是override
toString()
中的Node
方法。然后,您可以通过传递LinkedList
的head
来打印。您不需要实现任何类型的循环。
码:
public class LinkedListNode {
...
//New
@Override
public String toString() {
return String.format("Node(%d, next = %s)", data, next);
}
}
public class LinkedList {
public static void main(String[] args) {
LinkedList l = new LinkedList();
l.insertFront(0);
l.insertFront(1);
l.insertFront(2);
l.insertFront(3);
//New
System.out.println(l.head);
}
}