初学者Java不需要构造函数上的参数错误 [英] Beginner Java required no arguments error on constructor
问题描述
因此,作为一个类的作业,我试图制作一个简单的圆形类,然后将其用作构造函数。
这是我的课程代码:
So as an assignment for a class i'm trying to make a simple circle class and then use it as an constructor. Here is my class code:
public class Circle
{
private double radius;
private double pi;
public void setRadius(double rad)
{
radius = rad;
}
public double getRadius()
{
return radius;
}
public double getArea()
{
return pi * radius * radius;
}
public double getDiameter()
{
return radius * 2;
}
public double getCircumference()
{
return 2 * pi * radius;
}
}
这里是使用该类构造构造函数的程序:
Here's the program that uses the class to make a constructor:
import java.util.Scanner; //scanner class for input
public class CircleDemo
{
public static void main(String[]args)
{
double radiusIn; //gets radius from input
Scanner keyboard=new Scanner(System.in); //activates scanner class in program
System.out.print("Enter the radius of a circle: ");
radiusIn=keyboard.nextDouble();
Circle circularObject= new Circle(radiusIn);
System.out.println("The circle's area is" + circularObject.getArea());
System.out.println("The circle's diameter is" + circularObject.getDiameter());
System.out.println("The circle's circumference is" + circularObject.getCircumference());
}
}
,我得到错误:
Error :类Circle中的构造函数Circle不能应用于给定类型;
必需:无参数
:双
原因:实际参数和正式参数列表的长度不同
and i get the error: Error: constructor Circle in class Circle cannot be applied to given types; required: no arguments found: double reason: actual and formal argument lists differ in length
我什么都没看到我的代码有误,但随后我再次使用了老师给我们的示例。
I don't see anything wrong with my code, but then again i'm using the sample that my teacher gave us.
推荐答案
您正在调用构造函数这里
You are calling the constructor here
Circle circularObject= new Circle(radiusIn);
但是您的 Circle
类,该类与您要传入的参数匹配。返回您的 Circle
类,并定义一个构造函数,该构造函数使用 double
参数:
But there is no constructor defined in your Circle
class which matches the argument you are passing in. Return to your Circle
class and define the constructor which takes a double
argument:
public Circle(double val)
{
//Implementation
}
请注意,如果没有为类提供显式构造函数,Java会自动为您提供具有空实现,无参数的公共构造函数供您使用。一旦定义了第一个显式构造函数,该默认构造函数就消失了,这意味着您必须手动重新定义它。
Note that if you do not provide an explicit constructor for a class, Java will automatically provide you with an empty-implementation, no argument, public constructor for you to use. Once you define your first explicit constructor, that default constructor is gone, meaning you would have to re-define it manually.
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