java实现简单的链表增加，删除，显示

package com.liu.link;

public class LinkListCopy {
    //first为私有，不能动，当外部想查看内部时，为了安全需要，需要重新指定指针指向first
    private Link_1 first;
    public LinkListCopy()
    {
        first = null;
    }
    
    public boolean isEmpty()
    {
        return first==null;
    }
    
    public void insertFirst(int id,double dd)
    {
        Link_1 link = new Link_1(id,dd);
        link.next = first;
        first = link;
    }
    
    public Link_1 delete()
    {
        Link_1 temp;
        temp = first;
        first = first.next;
        return temp;
    }
    
    public void display()
    {
        System.out.println("link:");
        Link_1 current = first;
        while(current!=null)
        {
            
            current.displayLink();
            System.out.println("");
            current = current.next;
            
        }
    }
}

class Link_1
{
    public int iData;
    public double dData;
    public Link_1 next;
    
    public Link_1(int id,double dd)
    {
        iData = id;
        dData = dd;
    }
    
    public void displayLink()
    {
        System.out.print("{"+iData+", "+dData+"}");
    }
    
    
}

class LinkListCopyApp
{
    public static void main(String args[])
    {
        LinkListCopy link = new LinkListCopy();
        link.insertFirst(11, 1.11);
        link.insertFirst(22, 2.11);
        link.insertFirst(33, 3.11);
        link.insertFirst(44, 4.11);
        link.insertFirst(55, 5.11);
        
        link.display();
        
        while(!link.isEmpty())
        {
            Link_1 the = link.delete();
            System.out.print("Delete ");
            the.displayLink();
            System.out.println("");
        }
        link.display();
    }
}