Question

在底部的我的main方法中尝试测试空的DoublyLinkedList时，底部的toString（）方法给我上述错误。我的直觉告诉我，这可能是由于我正在实现的List接口引起的，因为单词“ List”在红色显示“类型已定义列表”中带有下划线，并且从该接口中提取了isEmpty（）方法。虽然不完全确定。希望这对任何人都不构成负担。提前致谢。

public class DoublyLinkedList<T> implements List<T> {

  /**
   * Node is a pair containing a data field and a pointers to
   * the previous and next nodes in the list.
   */
  class Node {
    T data;
    Node next, prev;

    Node(T data) {
      this(data, null, null);
    }

    Node(T data, Node prev, Node next) {
      this.data = data;
      this.prev = prev;
      this.next = next;
    }
  }

  Node head;  // always points to the headnode for this list
  int n;      // the number of nodes in this list, initially 0

  /**
   * Creates the empty list. 
   */
  public DoublyLinkedList() {
    // TODO: Create the headnode.
    // Note that the prev and next fields in the headnode should 
    // point back to the headnode.
      Node head = new Node(null);
      head.prev=head;
      head.next=head;

  }

  public String toString() {
      System.out.println("meeee");
    if (this.isEmpty())
      return "()";    
    Iterator<T> it = iterator();
    StringBuilder ans = new StringBuilder("(").append(it.next());
    while (it.hasNext())
      ans.append(" ").append(it.next());
    return ans.append(")").toString();
  }

 public static void main(String... args) {
    DoublyLinkedList<Integer> xs = new DoublyLinkedList<>();
    System.out.println(xs.toString());
}

interface List<T> extends Iterable<T> {
  void add(T x);  // simple add
  T remove(int i);
  T get(int i);
  boolean contains(T x);
  int size();
  default boolean isEmpty() {
    return size() == 0;
  }
}

java.lang.AbstractMethodError：方法DoublyLinkedList.isEmpty（）Z是抽象的吗？

0 个答案: