LinkedList的自定义实现

一、背景　　　　　　　　　　　　　　

LinkedList双向链表；

代码：

Node.java:

package com.cy.collection;

public class Node {
    Node previous;    //上一个node
    Object obj;        //node上值
    Node next;        //下一个node

    public Node(Object obj) {
        this.obj = obj;
    }
}

LinkedList.java:

package com.cy.collection;

/**
 * 自定义实现链表LinkedList
 */
public class LinkedList {
    private Node head;
    private Node tail;
    private int size;

    //add
    public void add(Object obj){
        Node n = new Node(obj);
        if(head==null){
            head = n;
            tail = n;
        }else{
            n.previous = tail;
            tail.next = n;
            tail = n;
        }
        size++;
    }

    //在指定下标位置，插入值
    public void add(int index, Object obj){
        rangeCheck(index);

        Node temp = node(index);
        Node newNode = new Node(obj);

        if(temp!=null){
            Node up = temp.previous;
            if(up==null){                //如果是在head节点前面插入
                newNode.next = temp;
                temp.previous = newNode;
                head = newNode;
            }else{
                up.next = newNode;
                newNode.previous = up;

                newNode.next = temp;
                temp.previous = newNode;
            }
            size++;
        }
    }

    //get
    public Object get(int index){
        rangeCheck(index);

        Node temp = node(index);
        if(temp!=null){
            return temp.obj;
        }

        return null;
    }

    public void remove(int index){
        Node temp = node(index);

        if(temp!=null){
            Node up = temp.previous;
            Node down = temp.next;

            if(up==null){                //如果remove的是head节点
                down.previous = null;
                head = down;
            }else if(down==null){        //如果remove的是tail节点
                up.next = null;
                tail = up;
            }else{                        //remove的是中间节点
                up.next = down;
                down.previous = up;
            }
            size--;
        }
    }
    
　　 //找到指定位置index的node
    public Node node(int index){
        Node temp = null;
        if(head!=null){
            if(index < (size>>1)){            //从head开始遍历
                temp = head;
                for(int i=0;i<index;i++){
                    temp = temp.next;
                }
            }else{                            //从tail开始遍历
                temp = tail;
                for(int i=size-1;i>index;i--){
                    temp = temp.previous;
                }
            }
        }
        return temp;
    }

    //size
    public int size(){
        return size;
    }

    //range check
    public void rangeCheck(int index){
        if(index<0 || index>=size){
            throw new RuntimeException("IndexOutOfBoundsException");
        }
    }
}

Test.java测试:

package com.cy.collection;

public class Test {

    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        list.add("aaa");
        list.add("bbb");
        list.add("ccc");

        System.out.println(list.size());

        list.add(2, "ddd");

        System.out.println(list.get(3));
        System.out.println(list.size());
    }

}

输出：

3
ccc
4