您好。我试图通过子类从超类调用一个方法,但不断收到错误。
我试图调用的方法是setDestination()
但是编译器一直给我错误“找不到符号 - 方法setDestination(java.lang.string)”我的讲师说这是一个简单的错过匹配的参数方法调用和方法,但我有类型String
的方法参数,所以我有点困惑。
我的代码是:
超级车辆:
public class Vehicle
{
// A unique ID for this vehicle
private String id;
// The next destination of this Vehicle.
private String destination;
/**
* Constructor for objects of class Vehicle
*/
public Vehicle(String id)
{
destination = null;
}
/**
* Return the ID of the Vehicle.
* @return The ID of the Vehicle.
*/
public String getID()
{
return id;
}
/**
* Return the destination of the Vehicle.
* @return The destination of the Vehicle.
*/
public String getDestination()
{
return destination;
}
/**
* Set the intented destination of the Vehicle.
* @param destination The intended destination.
*/
private void setDestination(String destination)
{
this.destination = destination;
}
}
子类Taxi
:
public class Taxi extends Vehicle
{
// The location of this taxi.
private String location;
// Whether it is free or not.
private boolean free;
/**
* Constructor for objects of class Taxi.
* @param base The name of the company's base.
* @param id This taxi's unique id.
*/
public Taxi(String base, String id)
{
super(id);
location = base;
free = true;
}
/**
* Book this taxi to the given destination.
* The status of the taxi will no longer be free.
* @param destination The taxi's destination.
*/
public void book(String destination)
{
setDestination(destination);
free = false;
}
/**
* Return the status of this taxi.
* @return The status.
*/
public String getStatus()
{
return getID() + " at " + location + " headed for " +
destination;
}
/**
* Return the location of the taxi.
* @return The location of the taxi.
*/
public String getLocation()
{
return location;
}
/**
* Indicate that this taxi has arrived at its destination.
* As a result, it will be free.
*/
public void arrived()
{
location = destination;
destination = null;
free = true;
}
}
任何帮助都非常感激。
答案 0 :(得分:6)
这是private
方法。您无法访问私有方法。将其更改为受保护。
您只能在班级中访问私人会员。
Modifier Class Package Subclass World
---------------------------------------------
public Y Y Y Y
protected Y Y Y N
no modifier Y Y N N
private Y N N N
http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html
答案 1 :(得分:4)
您已将setDestination
定义为private
private void setDestination(String destination)
因此您无法通过继承访问它。将其更改为protected
或“public”。了解有关访问修饰符here.
答案 2 :(得分:3)
私有修改器无法从课外访问。
答案 3 :(得分:1)
私有方法不会被继承,超类引用会调用自己的私有方法。
使用private void setDestination(String destination)
代替
public void setDestination(String destination)