K so my code is

[

/**
* Write a description of class Tank here.
*
* @author (your name)
* @version (a version number or a date)
*/

import java.util.Scanner;
class Tank
{
double TankRadius;
double TankArea = Math.PI * TankRadius * TankRadius;
double TankVolume;
double HoleRadius;
double HoleArea;
double VelocityoutofTank;
double VolumeLost;
double NewVolumeInTank;
double FuelHeight = 20;
double TankDiameter = 10;
double HoleDiameter = 2;
double WaterHeight;

double TankRadius()
{
return (TankDiameter) / 2;
}

double TankArea()
{
return Math.PI * TankRadius * TankRadius;
}

double TankVolume()
{
return FuelHeight * TankArea;
}

double HoleRadius()
{
return HoleDiameter / 2;
}

double HoleArea()
{
return Math.PI * HoleRadius * HoleRadius;
}

double VelocityoutofTank()
{
return 8.02 * Math.sqrt(WaterHeight);
}

double VolumeLost()
{
return VelocityoutofTank * HoleArea * 1;
}

double NewVolumeInTank()
{
return TankVolume - VolumeLost;
}

double FuelHeight()
{
return NewVolumeInTank / TankArea;
}

}

public class TankDrainer
{
public static void main (String[ ] args)
{

Scanner in = new Scanner(System.in);
Tank drainer = new Tank();
double TankRadius;

System.out.println("The tank radius: " + drainer.TankRadius());
TankRadius = in.nextDouble();
System.out.println("The tank area: " + drainer.TankArea());
System.out.println("The tank volume: " + drainer.TankVolume());
System.out.println("The hole radius: " + drainer.HoleRadius());
System.out.println("The hole area: " + drainer.HoleArea());
System.out.println("The Velocity out of tank: " + drainer.VelocityoutofTank());
System.out.println("The Volume Lost: " + drainer.VolumeLost());
System.out.println("The New Volume In Tank: " + drainer.NewVolumeInTank());
System.out.println("The Fuel Height: " + drainer.FuelHeight());

}

]


but I get 0 for tank area, volume, hole area, velocity out of tank..etc

can you plz tell me what im doing wrong?

I don't see any instruction where you initialized your variables, so by default they are all 0. When calculating the surface, the program calculates:



Initializing (giving an initial value to) your variables may solve the problem.