Question

我正在尝试将我的Vehicle类扩展为HumanPowered类 - 有一个每小时卡路里的字段。这是我第一次尝试扩展课程，所以我在这里有点困惑。

class Vehicle
{
String description;
String idNumber;
int numWheels;

public Vehicle(String aDescription, String aIdNumber, int aNumWheels)
{
    description = aDescription;
    idNumber = aIdNumber;
    numWheels = aNumWheels;
}
void setDescription (String aDescription)
{
    description = aDescription;
}
void setIdNumber (String aIdNumber)
{
    idNumber = aIdNumber;
}
void setNumWheels (int aNumWheels)
{
    numWheels = aNumWheels;
}
public String getDescription()
{
    return description;
}
public String getIdNumber()
{
    return idNumber;
}
public int getNumWheels()
{
    return numWheels;
}
public String toString()
{
    String result= String.format("ID: %s Description: %s Wheels: %d",idNumber,description,numWheels);
    return result;
}

}
class humanPowered extends Vehicle
{
int calories;
public humanPowered(String aDescription, String aIdNumber, int aNumWheels, int aCalories) //Error here
{
    description = aDescription;
    idNumber = aIdNumber;
    numWheels = aNumWheels;
    calories = aCalories;   
}
void setCalories (int aCalories)
{
    calories = aCalories;
}
public int getCalories()
{
    return calories;
}
public String toString()
{
    String result= String.format("ID: %s Description: %s Wheels: %d Calories per Hour: %d",idNumber,description,numWheels, calories);
    return result;
}
}

我的构造函数为我的humanPowered类收到错误，上面写着“隐式超级构造函数Vehicle（）未定义。必须显式调用另一个构造函数。”我无法弄清楚我在哪里出错了。感谢您的帮助！

Answer 1

Vehicle没有默认构造函数，因此你必须调用它的构造函数形式humanPowered类，在其构造函数的第一行传递必需的参数。

public humanPowered(String aDescription, String aIdNumber, int aNumWheels, int aCalories)    
{
   super(aDescription,aIdNumber,aNumWheels);
   ...//other code
}

要记住的要点：

每个类都有默认构造函数，它是无参数构造函数
如果类创建传递参数的构造函数，则默认情况下不会创建构造函数
默认情况下，每个构造函数都调用其超类

Java：扩展类

1 个答案: