编写测试课程的课堂方法

Question

public class CirclTest{
    public static void main(String[] args){
        Circle first=new Circle('R',3.0);

        Circle first=new Circle('R',3.0);

        Circle second=new Circle();

        System.out.println("first's radius is " + first.getRadius());

        System.out.println("first's area is " + first.getArea());
        System.out.println("second's area is " + second.getArea());

        if(first.hasLargerAreaThan(20)){
            System.out.println("first's area is larger than 20. ");
        }else{
            System.out.println("first's area is smaller than 20. ");
        }
    }
}

So i am supposed to write a circle class.This is what i have done.

public class Circle{
    private double radius=0.0;
    private double area=0.0;
    private char colour=' ';

    public Circle(char colour,double radius){
        this.colour=colour;
        this.radius=radius;
    }

    public Circle(){
        radius=0;
        colour='B';
    }


    public char getColour(){
        return colour;
    }
    public double getRadius(){
        return radius;
    }

    public double getArea(){
        return area;
    }


    }

I am actually confused on how to write a class.Like i know i need to initialize the variables by private etc.And i need to build a constructor but somehow this code above does not work.the test method is correct.But i have to use it to implement my class.

Answer 1

You're declaring the variable

Circle first

twice. If you want to reassign its value, just do

first=new Circle('R',3.0);

And inside the if statement you're calling

first.hasLargerAreaThan(20)

when I don't see such a method defined in your class.

Answer 2

Can you please what you mean by the code does not work? If you are referring to area not getting calculated correct and is always 0, that is happening because you have a default value for the same as 0 and are never calculating it. You might want to put calculation logic in getArea() method.

Answer 3

First, you're going to want to use a testing framework to assert the validity of your code, if that's what is required. Look into JUnit .

A sample assertion of if the area was larger than some value would be written like this.

@Test
public void assertArea_calculatedProperly() {
    //given that the radius is 5,
    Circle c = new Circle('R', 5);

    //when I get the area...
    double result = c.getArea();

    //then I expect it to be around 78.53981634.
    assertTrue(result < 78.6);
    assertTrue(result > 78.5);
}

Second, your getArea isn't actually getting the area. There's nothing in your code to retrieve, then calculate the area. You're not even using Math.PI . I would recommend that you implement that - but use the unit test as a valid way to assert that you're going to get an appropriate response back.