无效的方法声明;返回类型需要 修复时第 10 行 + 14 个附加错误

Question

G'day 我有点新手，我一直在努力寻找为什么这个练习似乎无法编译。任何和所有的建议将不胜感激！

目前，错误是

"java：10：错误：无效的方法声明;返回类型需要公共设置半径(双 r({">

但是，当我将public setRadius更改为public double setRadius时，我得到 14 个错误。以下是其中的一些

CarApp.java：59：错误：找不到符号

            System.out.println("Radius for Car 2 = " + radus2);
                                                      ^

CarApp.java：63：错误：找不到符号

        System.out.println("Radius for Car 3 = " + radius3);
                                                      ^

CarApp.java：65：错误：找不到符号

        car1.car(22.0);
               ^

CarApp.java：67：错误：变量 cir 已在方法 main(String[]( 中定义

        double cir = circle1.calCircumference(); 
               ^

CarApp.java：68：错误：变量区域已在方法 main(String[]( 中定义

        double area = car1.calArea();
               ^

CarApp.java：70：错误：找不到符号

class Car {
    private static double r;
    public static void Car(double rd) {
        r = rd;
    }
    public Car(Car Source){
        this.r = Source.r;
    }
public setRadius (double r){
    radius=r;
}
public double getRadius(){ 
    return this.r;
}
public double calCircumference(){
        return 2 * Math.PI * r;
}
public static double calArea() {  
        return Math.PI * r * r;
    }
}
class CarApp {
    public static void main(String[] args)
    {
        Car car1 = new Car();
        Car car2 = new Car(car1);
        Car car3 = new Car(car2);
        double rd = Double.parseDouble(args[0]);
        System.out.println( "Car radius = " + rd );
        car1.car(rd);
        double cir = circle1.calCircumference(); 
        double area = circle1.calArea();
        car2.car(rd);
        double cir2 = circle2.calCircumference(); 
        double area2 = circle2.calArea();
        double radius2 = circle2.getRadius();

        car3.car(rd);
        double cir3 = circle3.calCircumference(); 
        double area3 = circle3.calArea();
        double radius3 = circle3.getRadius();
        System.out.println("Before");
        System.out.println("Circumference for Car 1 = " + cir);
        System.out.println("Area for Car 1 = " + area);
        System.out.println("");
        System.out.println("Circumference for Car 2 = " + cir2);
        System.out.println("Area for Car 2 = " + area2);
        System.out.println("Radius for Car 2 = " + radius2);
        System.out.println("");
        System.out.println("Circumference for Car 3 = " + cir3);
        System.out.println("Area for Car 3 = " + area3 );
        System.out.println("Radius for Car 3 = " + radius3);
        car1.car(22.0);
        double radius1 = car1.getRadius();      
        double cir = car1.calCircumference(); 
        double area = car1.calArea();
        car2.car(rd);
        double cir21 = car2.calCircumference(); 
        double area21 = car2.calArea();
        double radius21=car2.getRadius();
        car3.setRadius(10.0);
        double cir31 = car2.calCircumference(); 
        double area31 = car2.calArea();
        double radius31 = car2.getRadius();     
        System.out.println("After");
        System.out.println("Radius for Car 1 = " + radius1);
        System.out.println("");
        System.out.println("Circumference for Car 2 = " + cir21);
        System.out.println("Area for Car 2 = " + area21);
        System.out.println("Radius for Car 2 = " + radius21);
        System.out.println("");
        System.out.println("Radius for Car 3 = " + radius31);
    }
}

Answer 1

代码有很多错误，请尝试通过我认为您要做的事情来修复它们......

class Car {
    private static double r;
    public Car() {
        r = 0.0;
    }
    public Car(double rd) {
        r = rd;
    }
    public Car(Car Source){
        this.r = Source.getRadius();
    }
    public void setRadius (double r){
        this.r=r;
    }
    public double getRadius(){
        return this.r;
    }
    public double calCircumference(){
        return 2 * Math.PI * r;
    }
    public static double calArea() {
        return Math.PI * r * r;
    }
}
class CarApp {
    public static void main(String[] args)
    {
        Car car1 = new Car();
        Car car2 = new Car(car1);
        Car car3 = new Car(car2);
        double rd = Double.parseDouble(args[0]);
        System.out.println( "Car radius = " + rd );
        car1.setRadius(rd);
        // need define circle1 like `Circle circle1 = new Circle(...)`
        double cir = circle1.calCircumference();
        double area = circle1.calArea();
        car2.setRadius(rd);
        // need to define circle2, like the above
        double cir2 = circle2.calCircumference();
        double area2 = circle2.calArea();
        double radius2 = circle2.getRadius();

        car3.setRadius(rd);
        // need to define circle3, like the above above
        double cir3 = circle3.calCircumference();
        double area3 = circle3.calArea();
        double radius3 = circle3.getRadius();
        System.out.println("Before");
        System.out.println("Circumference for Car 1 = " + cir);
        System.out.println("Area for Car 1 = " + area);
        System.out.println("");
        System.out.println("Circumference for Car 2 = " + cir2);
        System.out.println("Area for Car 2 = " + area2);
        System.out.println("Radius for Car 2 = " + raduis2);
        System.out.println("");
        System.out.println("Circumference for Car 3 = " + cir3);
        System.out.println("Area for Car 3 = " + area3 );
        System.out.println("Radius for Car 3 = " + raduis3);
        car1.setRadius(22.0);
        double radius1 = car1.getRadius();
        cir = car1.calCircumference();
        area = car1.calArea();
        car2.setRadius(rd);
        double cir21 = car2.calCircumference();
        double area21 = car2.calArea();
        double radius21=car2.getRadius();
        car3.setRadius(10.0);
        double cir31 = car2.calCircumference();
        double area31 = car2.calArea();
        double radius31 = car2.getRadius();
        System.out.println("After");
        System.out.println("Radius for Car 1 = " + raduis1);
        System.out.println("");
        System.out.println("Circumference for Car 2 = " + cir21);
        System.out.println("Area for Car 2 = " + area21);
        System.out.println("Radius for Car 2 = " + raduis21);
        System.out.println("");
        System.out.println("Radius for Car 3 = " + raduis31);
    }
}

希望对...