public abstract class 车
{
  public int 轮子;
  public abstract void 移动();
}

 public class 跑车 extends 车
 {
    public void 移动() 
    {
        System.out.println("我在移动");
    }   
   public void 引擎类型()  //属于自己(跑车)的行为
   {
      System.out.println("高级引擎");
   }
   轮子=4;
 }

 public class 自行车 extends 车
 {
   public void 移动() 
   {
      System.out.println("我在移动");
   }   
   public void 爆胎()  //属于自己(自行车)的行为
   {
      System.out.println("我走不动了");
   }
   轮子=2;
 }

public interface TCP协议
{
   public void 打开端口();
   public void 关闭端口()；
}

public abstract class 车
 {
   public int 轮子;
   public abstract void 移动();
   public String 我是什么()
   {
      return "车子";
   }
 }

The interface keyword takes the abstract concept one step further. You could think of it as a “pure” abstract class. It allows the creator to establish the form for a class: method names, argument lists, and return types, but no method bodies. An interface can also contain fields, but these are implicitly static and final. An interface provides only a form, but no implementation.
An interface says, “This is what all classes that implement this particular interface will look like.” Thus, any code that uses a particular interface knows what methods might be called for that interface, and that’s all. So the interface is used to establish a “protocol” between classes. (Some object-oriented programming languages have a keyword called protocol to do the same thing.)