帮我找出错误：invalid method declaration；需要返回类型

Question

这是我的 java 类的最后一个家庭作业，我一直试图通过编译器运行它，但我不明白代码有什么问题。

在阅读了如何解决返回类型问题后，我尝试使用 void 但这只会让事情变得更糟，也许我把 void 放在了错误的地方。

public class Exercise09_01 {

    private double width = 1;

    private double height = 1;

    public Rectangle() {

    }

    public Rectangle(double newWidth, double newHeight) {

        width = newWidth;

        height = newHeight;

    }

    public double getArea() {

        return width * height;

    }

    public double getPerimeter() {

        return 2 * (width + height);

    }

    public static void main(String[] args) {

        Rectangle rectangle1 = new Rectangle(4, 40);

        System.out.println("The area of a 4.0 x 40.0 Rectangle is " + 

        rectangle1.getArea());

        System.out.println("The perimeter of a 4.0 x 40.0 Rectangle is " + 

        rectangle1.getPerimeter());

        Rectangle rectangle2 = new Rectangle(3.5, 35.9);

        System.out.println("The area of a 3.5 x 35.9 Rectangle is " + 

        rectangle2.getArea());

        System.out.println("The perimeter of a 3.5 x 35.9 Rectangle is " + 

        rectangle2.getPerimeter());

    }

}

这是我这门课的最后一个家庭作业，我只想在任何帮助下完成它，我们将不胜感激。

Answer 1

构造函数名称应与类名同名    public class Exercise09_01 {        private double width = 1;        private double height = 1;        public Exercise09_01() {        }        public Exercise09_01(double newWidth, double newHeight) {            width = newWidth;            height = newHeight;        }   }

Answer 2

public class Exercise09_01 {private double width = 1;private double height = 1;public Exercise09_01() {}public Exercise09_01(double newWidth, double newHeight) {width = newWidth;height = newHeight;}public double getArea() {return width * height;}public double getPerimeter() {return 2 * (width + height);}public static void main(String[] args) {Exercise09_01 rectangle1 = new Exercise09_01(4, 40);System.out.println("The area of a 4.0 x 40.0 Rectangle is " + rectangle1.getArea());System.out.println("The perimeter of a 4.0 x 40.0 Rectangle is " + rectangle1.getPerimeter());Exercise09_01 rectangle2 = new Exercise09_01(3.5, 35.9);System.out.println("The area of a 3.5 x 35.9 Rectangle is " + rectangle2.getArea());System.out.println("The perimeter of a 3.5 x 35.9 Rectangle is " + rectangle2.getPerimeter());}}感谢所有帮助，这是通过编译器的代码。只是把它留在这里供未来的访客使用。

Answer 3

您的代码中的错误是您的类名和构造函数名称不同。您有两种选择，一种是将构造函数重命名为Exercise01_01或将返回类型重命名Rectangle为 void。public class Exercise01_01 {    private double width = 1;    private double height = 1;    public Exercise01_01() {    }    public Exercise01_01(double newWidth, double newHeight) {        width = newWidth;        height = newHeight;    }    public double getArea() {        return width * height;    }    public double getPerimeter() {        return 2 * (width + height);    }    public static void main(String[] args) {        Exercise01_01 rectangle1 = new Exercise01_01(4, 40);        System.out.println("The area of a 4.0 x 40.0 Rectangle is " + rectangle1.getArea());        System.out.println("The perimeter of a 4.0 x 40.0 Rectangle is " + rectangle1.getPerimeter());        Exercise01_01 rectangle2 = new Exercise01_01(3.5, 35.9);        System.out.println("The area of a 3.5 x 35.9 Rectangle is " + rectangle2.getArea());        System.out.println("The perimeter of a 3.5 x 35.9 Rectangle is " + rectangle2.getPerimeter());    }}

Answer 4

public Rectangle() {}就Java而言，这是一种方法。所有的方法都必须有一个返回类型。public Rectangle(double newWidth, double newHeight) {width = newWidth;  height = newHeight;  }和这里一样。你真的不需要第一个，除非你真的需要能够在没有设置这些值的情况下制作一个。您可以重命名它们，但您可能只想重命名类Rectangle