Java数据结构之双端链表原理与实现方法

public class FirstLastLinkList {  //头  private Node first;  //尾  private Node last;  public FirstLastLinkList(){    first = null;    last = null;  }    public void insertFirst(long value){    Node newNode = new Node(value);    if (first == null) {      last = newNode;    }else {      //把first节点往下移动      newNode.next = first;    }    //把插入的节点作为新的节点    first = newNode;  }    public void insertLast(long value){    Node newNode = new Node(value);    if (first == null) {      first = newNode;    }else {      last.next = newNode;    }    //把最后个节点设置为最新的节点    last = newNode;  }  public boolean isEmpty(){    return first == null;  }    public Node deleteFirst(){    if (first == null) {      throw new RuntimeException("链表数据不存在");    }    if (first.next == null) {      last = null;    }    Node temp = first;    first = temp.next;    return temp;  }  public Node deleteByKey(long key){    Node current = first;    Node last = first;    while(current.data != key){      if (current.next == null) {        System.out.println("没找到节点");        return null;      }      last = current;      current = current.next;    }    if (current == first) {      //return deleteFirst();      //指向下个就表示删除第一个      first = first.next;    }else {      last.next = current.next;    }    return current;  }    public void display(){    if (first == null) {      //throw new RuntimeException("链表数据不存在");      return;    }    Node current = first;    while(current != null){      current.display();      current = current.next;    }    System.out.println("---------------");  }    public Node findByValue(long value){    Node current = first;    while(current != null){      if (current.data != value) {        current = current.next;      }else {        break;      }    }    if (current == null) {      System.out.println("没找到");      return null;    }    return current;  }    public Node findByKey(long key) {    Node current = first;    while (current.data != key) {      if (current.next == null) {        System.out.println("没找到");        return null;      }      current = current.next;    }    return current;  }    public Node findByPosition(int position){    Node current = first;    //为什么是position - 1，因为要使用遍历，让current指向下一个， 所以position - 1的下个node就是要找的值    for (int i = 0; i < position - 1 ; i++) {      current = current.next;    }    return current;  }  public static void main(String[] args) {    FirstLastLinkList linkList = new FirstLastLinkList();    linkList.insertFirst(21);    linkList.insertFirst(22);    linkList.insertFirst(23);    linkList.insertLast(24);    linkList.insertLast(25);    linkList.insertLast(26);    linkList.insertLast(27);    linkList.display();    System.out.println("---查找-------------------------------------");    linkList.findByKey(25).display();    System.out.println("--删除first-------------------------------------");    //linkList.deleteFirst().display();    ///linkList.deleteFirst().display();    //linkList.deleteFirst().display();    //linkList.deleteFirst().display();    System.out.println("-删除指定值---------------------------------------");    linkList.deleteByKey(27).display();    linkList.deleteByKey(21).display();    System.out.println("----------------------------------------");    linkList.display();  }}