为什么我的代码没有打印出新的气球体积？

Question

I'm a beginner at Java and I'm having trouble understanding why my "Inflate" and "getVolume" methods aren't working. I'm sure they're just simple problems but I'd still like some help so I can fix my code and improve!

import java.util.Scanner;

public class Balloon
{
    public static void main(String[] args)
    {
        Scanner multiplier = new Scanner(System.in);
        System.out.println("How much should the radius be increased by? ");

        double amount = multiplier.nextDouble();

        double radius = 0;

        public void Inflate(double amount);
        {       
            double newRadius = radius + amount;
        }
        public double getVolume();
        {
            double sVolume = (4/3)*Math.PI*(newRadius*newRadius*newRadius);
            System.out.print(sVolume);
        }
    }
}

Answer 1

I suppose that Ballon is an object you can inflate and has an state of radius, you can moreover get the volume.

The main method here is only to test if balloon works correctly

public class Balloon {

private double radius = 0;

public static void main(String[] args) {
    Scanner multiplier = new Scanner(System.in);
    System.out.println("How much should the radius be increased by? ");

    Balloon balloon=new Balloon();
    double amount = multiplier.nextDouble();
    balloon.inflate(amount);
    double volume = balloon.getVolume();
    System.out.print(volume);
}

public void inflate(double amount) {
    radius = radius + amount;
}

public double getVolume() {
    double sVolume = (4 / 3) * Math.PI * (Math.pow(radius, 3));
    return sVolume;
}
}