Thread: Help With BalloonTester

I am supposed to write a Tester to get the current volume of a balloon that starts with a radius of 0 after it is inflated.

This is the balloon:

public class Balloon
{
 
	private double savedRadius;//instance variable
 
	/**constructor!!
      Constructs a balloon with a radius
   */
   public Balloon(double radius)
	{
	savedRadius = radius;
}
 
	//doubles the radius of the balloon
	public void inflate(double radius)
   {
      savedRadius = savedRadius + radius; //returning total, accumilating 
      }
 
		/**
      Gets the volume*/
 
		 public double getVolume()
 
   {
      double volume = (1.33 * 3.14 * savedRadius * savedRadius * savedRadius);
		return volume;
   }
   }

This is what I have so far for the BalloonTester. I have tried multiple different things and I keep getting errors, I am at my wits end.

public class BalloonTester
{
   /**
 
   */
   public static void main(String[] args)
 
   {
 
      Balloon newBalloon = new Balloon(0);
 
      System.out.println("Current volume of the ballon: "+newBalloon.getVolume());
 
	 }
}

I am not asking for it to be done for me, I just need to know where to start as this is getting on my nerves.

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I have tried multiple different things and I keep getting errors

Post code with the full text of its corresponding errors so we know what to help you with.

Originally Posted by GregBrannon

Welcome to the forum! Thanks for taking the time to learn how to post code correctly. If you haven't already, please read this topic to learn other useful info for new members.



Post code with the full text of its corresponding errors so we know what to help you with.

Well one of the things I tried was ..

public class BalloonTester
{
   /**
 
   */
   public static void main(String[] args)
 
   {
 
      Balloon newBalloon = new Balloon(0);
      double radius;
      double inflate;
      newBalloon.inflate();
 
 
      System.out.println("Current volume of the ballon: "+newBalloon.getVolume());
 
	 }
}

the error is :
BalloonTester.java:21: error: method inflate in class Balloon cannot be applied to given types;
newBalloon.inflate();
^
required: double
found: no arguments
reason: actual and formal argument lists differ in length
1 error

I know that isn't enough, I am really lost for some reason.

The error message is quite clear:

required: double
found: no arguments

The method you tried to call requires a double argument and you were giving it no arguments.
Give the method a double as an argument and this error will be gone.

I tried this:

 
public class BalloonTester
{
   /**
 
   */
   public static void main(String[] args)
 
   {
 
      Balloon newBalloon = new Balloon(0);
      double inflate;
      double radius;
      newBalloon.inflate(radius);
 
 
 
      System.out.println("Current volume of the ballon: "+newBalloon.getVolume());
 
	 }
}

and got

variable radius might not have been initialized
newBalloon.inflate(radius);
^"

Java requires that local variables be initialized before use. This can be as simple as:

double radius = 0.0;

Originally Posted by GregBrannon

Java requires that local variables be initialized before use. This can be as simple as:

double radius = 0.0;

Thanks. I am still missing a step somewhere. I keep getting 0.0 as the current volume if I use:

 
public class BalloonTester
{
   /**
 
   */
   public static void main(String[] args)
 
   {
 
      Balloon newBalloon = new Balloon(0);
      double radius = 0.0;
      double inflate;
      newBalloon.inflate(radius);
 
 
 
      System.out.println("Current volume of the ballon: "+newBalloon.getVolume());
 
	 }
}

I thought that newBalloon.inflate(radius); would inflate it but there is something I am missing.

Try other numbers, play with it a bit.

You try to inflate it with 0.0, what do you think is going to happen?

Originally Posted by Cornix

You try to inflate it with 0.0, what do you think is going to happen?

well that is part of the issue. The problem says the balloon starts with a radius of 0. and the class we were provided with says

//doubles the radius of the balloon
	public void inflate(double radius)
   {
      savedRadius = savedRadius + radius; //returning total, accumilating 
      }

I feel like I am supposed to use savedRadius somewhere in the tester but every time I tried I got an error. But even if I am, how are you supposed double a radius of 0? The book says inflate it by the given amount, but we were not given an amount.

The comment is clearly wrong as you can read from the method:

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

The balloons radius is saved in the field "savedRadius". The inflate method tages a double value as its argument and increments the saved radius by this value.
If you call "inflate(3);" then the new radius will be the old radius plus 3. If you call "inflate(0);" then the new radius will be equal to the old radius.