Question

我有一个类和一个名为contains的方法-检查列表是否包含给定的项目。我收到一个StackOverflow错误，想知道为什么。

我创建了列表，并在列表中添加了5个字符串。我正在检查字符串元素之一是否在列表中（如果是，则为true，否则为false）

 package arraylist_linkedList;

 import java.util.ArrayList;
 import java.util.Arrays;

  /**
 * WordList is a singly linked list of Strings. It is designed to      demonstrate
  * how linked structures work.
  * 
  * @author ..........
  */
   public class WordList {
private Node head;
private Node tail;
private int n; // number of words in the list
static WordList list = new WordList();
/**
 * Node of LinkedList that stores the item and a single reference to the next
 * node.
 */
private class Node {
    private String item;
    private Node next;
}

/**
 * Adds a node containing the new item at the end of the list.
 * 
 * @param newItem
 */
public void append(String newItem) {
    // create a new node based on the word provided by the user
    Node newNode = new Node();
    newNode.item = newItem;

    if (isEmpty()) {
        head = newNode;
        tail = newNode;
    } else {
        tail.next = newNode;
        tail = newNode;
    }
    n++;
}

/**
 * Adds a node containing the new item at the front of the list.
 * 
 * @param newItem
 */
public void prepend(String newItem) {
    Node newNode = new Node();
    newNode.item = newItem;
    newNode.next = head;
    head = newNode;
    n++;

    if (tail == null) {
        tail = head;
    }
    n++;
}

/**
 * Returns the index of the first occurrence of the specified item. If the
 * specified item in not part of the list the method indexOf returns -1
 * 
 * @param item
 * @return index of the first occurrence of the item; -1 if the word was not
 *         found.
 */
public int indexOf(String item) {

    return -1; // TODO 3
}

/**
 * Checks whether the list contains the given item.
 * 
 * @param item
 * @return true if the item is contained in the list; false otherwise.
 */
public boolean contains(String item) {
    if (list.contains(item)) {
        return true;
    }
    return false; // TODO
}

/**
 * Returns the number of elements in the list
 * 
 * @return the number of elements
 */
public int size() {
    return n;
}

/**
 * Determines whether the list is empty or not.
 * 
 * @return true if there are no elements in the list.
 */
public boolean isEmpty() {
    return n == 0;
}

@Override
public String toString() {
    StringBuilder sb = new StringBuilder();
    Node current = head;

    while (current != null) {
        sb.append(current.item).append(" ");
        current = current.next;
    }

    return sb.toString();
}

/* * * * * * * * Test Client * * * * * * */
public static void main(String[] args) {

    //print the list 
    System.out.println("size: " + list.size());

    // print The list is empty. or The list is not empty.
    // use a ternary operator to check whether the list is empty
    System.out.println(list.isEmpty() ? "List is empty" : "List is not empty" );

    // add words to list
    list.append("ant");
    list.append("bat");
    list.append("cow");
    list.append("dog");

    //print list 
    System.out.println("list: " + list);

    //add new item at the front of the list
    list.prepend("mouse");
    System.out.println("list: " + list);

    System.out.println("list contains: " + list.contains("ant"));



}

  }

错误消息：

线程“主”中的异常java.lang.StackOverflowError 在arraylist_linkedList.WordList.contains（WordList.java:83）

Answer 1

这里：

public boolean contains(String item) {
   if (list.contains(item))

在您的WordList实例上，您调用contains()。该方法...将转换为包含其自身的 one 静态WordList，然后再次调用contains()。再次，...

您在这里创建了无尽的递归。如何实施更好的解决方案取决于您要实现的目标。您最有可能的起点：

static WordList list = new WordList();

已经“错误”。您导入了ArrayList，所以为什么您的list不是ArrayList？无论如何，这个列表是 static ，顺便说一句。

因此：您的“每个对象”（不是静态的）list()方法在类的那个 static 列表字段上调用“自身”。那行不通，从概念上讲也没有意义。

包含特定元素的列表

1 个答案: