java - 为什么我的类显示为未使用，因此无法编译我的程序？

Question

对于java来说非常新，在我的类(class)(在学校没有这个程序)中，我们将设计一个存储重量的类和一个返回运费的方法。我显然对自己在这里所做的事情感到非常困惑。我有这段代码，但甚至无法编译，因为它显示我的类未被使用。任何帮助都会很棒。

import javax.swing.JOptionPane;

public class ShippingCharges {
    public float weight;

    public void myPublicMethod() {
        weight = Float.parseFloat(JOptionPane.showInputDialog(null, "What is the weight in kg?: ", JOptionPane.QUESTION_MESSAGE));
    }

    public static double main(String[] args) {
        ShippingCharges charge = new ShippingCharges();
        charge.myPublicMethod();

        if (charge.weight >= 2) {
            System.out.println("The shipping charge for 2kg or less for every 500 miles is $1.10");
            return 1.10;
        }
        if (charge.weight > 2 && charge.weight <= 6) {
            System.out.println("The shipping charge for over 2kg up to 6kg " +
                    "for every 500 miles is $2.20");
            return 2.20;
        }
        if (charge.weight > 6 && charge.weight <= 10) {
            System.out.println("The shipping charge for over 6kg up to 10kg " +
                    "for every 500 miles is $2.20");
            return 3.70;
        } else {
            System.out.println("The shipping charge for anything over 10kg" +
                    "for every 500 miles is $4.80");
            return 4.80;
        }
    }
}

如果之前有人问过这个问题，我也很抱歉。好像没找到

Answer 1

main 不返回 double 值。双返回应该在你的方法上。 main 的返回类型为 void。

试试这个:我冒昧地将 float 更改为双倍。如果需要，您可以将它们改回来。

public class ShippingCharges {
    public double weight;

    public static double myPublicMethod() {
        ShippingCharges charge = new ShippingCharges();
        double weight = Double.parseDouble(JOptionPane.showInputDialog(null, "What is the weight in kg?: ", JOptionPane.QUESTION_MESSAGE));
        if (charge.weight >= 2) {
            System.out.println("The shipping charge for 2kg or less for every 500 miles is $1.10");
            return 1.10;
        }
        if (charge.weight > 2 && charge.weight <= 6) {
            System.out.println("The shipping charge for over 2kg up to 6kg " +
                    "for every 500 miles is $2.20");
            return 2.20;
        }
        if (charge.weight > 6 && charge.weight <= 10) {
            System.out.println("The shipping charge for over 6kg up to 10kg " +
                    "for every 500 miles is $2.20");
            return 3.70;
        } else {
            System.out.println("The shipping charge for anything over 10kg" +
                    "for every 500 miles is $4.80");
            return 4.80;
        }
    }


    public static void main(String[] args) {

        myPublicMethod();

    }
}