Java小练习，双向链表实现

import java.lang.*;

public class MainJava {
    public static void main(String[] args) {
        TList list = new TList();
        for(int i = 0; i < 10; i++){
            list.push_back(i);
        }
        for(int i = -1; i >= -10; i--){
            list.push_front(i);
        }
        list.print();
    }
}
class Node{
    public int val;
    public Node next;
    public Node pre;
    public Node(int val){
        this.val = val;
    }
}
class TList{
    private Node tail;
    private Node head;
    public TList(){
        head = null;
        tail = null;
    }
    public void pop_front(){
        head = head.next;
        head.pre = null;
    }
    public void pop_back(){
        tail = tail.pre;
        tail.next = null;
    }
    public void push_back(int val){
        if(head == null){
            head = new Node(val);
            tail = head;
        }
        else {
            tail.next = new Node(val);
            tail.next.pre = tail;
            tail = tail.next;
        }
    }
    public void push_front(int val){
        if(head == null){
            head = new Node(val);
            tail = head;
        }
        else{
            head.pre = new Node(val);
            head.pre.next = head;
            head = head.pre;
        }
    }
    public void print(){
        Node ptr = this.head;
        System.out.print('[');
        while(ptr!=null) {
            System.out.print(ptr.val);
            if(ptr.next!=null)
                System.out.print(", ");
            ptr = ptr.next;
        }
        System.out.println(']');
    }
}