java链表

有一段时间没看数据结构了，导致链表有些生疏了，特别是java链表，改怎么写了···
额，好吧，看来以前是没学懂啊，不然怎么会忘了，再来一次

public class Node {
    private Object data;
    private Node next;

    public Node(Object data,Node next){
        this.data = data;
        this.next = next;
    }

    public Object getData(){
        return this.data;
    }

    public void setData(Object data){
        this.data = data;
    }

    public Node getNext(){
        return this.next;
    }

    public void setNext(Node next){
        this.next = next;
    }
}

public class List {
    private Node head;
    private int length;

    public List(){
        head = new Node(null,null);
        length = 0;
    }

    public Node getHead(){
        return this.head;
    }

    public void addHead(Object data){
        Node node = new Node(data,null);
        node.setNext(head.getNext());
        head.setNext(node);
        length++;
    }

    public void addTail(Object data){
        Node node = new Node(data,null);
        Node temp = head;
        while(null != temp.getNext()){
            temp = temp.getNext();
        }
        temp.setNext(node);
        length++;
    }

    public void addByIndex(Object data,int index){
        Node node = new Node(data,null);
        Node temp = head;
        for(int i=0;i<index-1;i++){
            temp = temp.getNext();
        }
        node.setNext(temp.getNext());
        temp.setNext(node);
        length++;
    }

    public void deleteByIndex(int index){
        if(index<1 || index>length){
            System.out.println("指定位置不存在");
        }else{
            Node temp = head;
            for(int i=0; i<index-1;i++){
                temp = temp.getNext();
            }
            temp.setNext(temp.getNext().getNext());
            length--;
        }
    }

    public void deleteAll(){
        head.setNext(null);
    }

    public void findByIndex(int index){
        if(index<1 || index>length){
            System.out.println("指定位置不存在");
        }else{
            Node temp = head;
            for(int i=0;i<index-1;i++){
                temp = temp.getNext();
            }
            System.out.println("位置"+index+"的元素是："+temp.getNext().getData());
        }
    }

    public void print(){
        Node temp = head.getNext();
        for(int i=0;i<length;i++){
            System.out.print(" "+temp.getData());
            temp = temp.getNext();
        }
    }

    public void lengthPP(){
        this.length++;
    }
}

public class Instance {
    public static void main(String[] args){
        //造一个随机数组
        int length = 9;
        int[] array = new int[length];
        array[length-2]=7;
        array[length-1]=7;
        for(int i=0;i<length-3;i++){
            array[i] = (int) (Math.random()*10);
        }

        for(int i=0;i<length;i++){
            System.out.print(array[i]+" ");
        }
        System.out.println();

        //找出随机数组中相等的数
        for(int i=0;i<length;i++){
            for(int j=0;j<length;j++){
                if((i < j) && (array[i] == array[j]))
                    System.out.println(i+":"+array[i]+"等于 "+j+":"+array[j]);
            }
        }

        //使用单链表对随机数组进行排序
        List list = new List();
        Node head = list.getHead();
        list.addHead(array[0]);
        Node temp = head;
        for(int i=1;i<length;i++){
            temp = head;
            while(array[i] > Integer.valueOf(temp.getNext().getData().toString())){
                temp = temp.getNext();
                if(temp.getNext()==null)
                    break;
            }
            if(temp.getNext() == null){
                temp.setNext(new Node(array[i],null));
            }else{
                Node node = new Node(array[i],null);
                node.setNext(temp.getNext());
                temp.setNext(node);
            }
            list.lengthPP();
        }

        list.print();

    }
}