Thread: Code won't let me remove integer.

EDIT: New issue. My program gives me an error when I try to "digUp" the purse. The error appears in the purse class.

import java.io.*;
public class Purse
{
//Fields
public double gp;
public double gold;
public double silver;
public double copper;
public double platinum;
public static final double GOLD_VALUE = 1;
public static final double SILVER_VALUE = 1/10.0;
public static final double COPPER_VALUE = 1/100.0;
public static final double PLATINUM_VALUE = 10/1;
//Constructors
public static void main(String[] args)
{
//>>>>>>>>>>***** HERE is the println for the values <<<<<<<<<<<*****
System.out.println(GOLD_VALUE);
System.out.println(SILVER_VALUE);
System.out.println(COPPER_VALUE);
System.out.println(PLATINUM_VALUE);
//>>>>>>>>>>***** HERE ends the println for the values <<<<<<<<<<<*****
}
public Purse()
{
//initialize
gp=0;
gold=0;
silver=0;
copper=0;
platinum=0;
}
 
//Methods
public void addGold(double gold)
{
gp+=gold*GOLD_VALUE;
}
public void addSilver(double silver)
{
gp+=silver*SILVER_VALUE;
}
public void addCopper(double copper)
{
gp+=copper*COPPER_VALUE;
}
public void addPlat(double platinum)
{
gp+=platinum*PLATINUM_VALUE;
}
public boolean removeGold(double gold)
{
boolean enoughmoney=true;
if(gold>gp)
enoughmoney=false;
else
gp-=gold*GOLD_VALUE;
return enoughmoney;
}
public boolean removeSilver(double silver)
{
boolean enoughmoney=true;
if(silver>gp)
enoughmoney=false;
else
gp-=silver*SILVER_VALUE;
return enoughmoney;
}
public boolean removeCopper(double copper)
{
System.out.println(copper);
System.out.println(gp);
boolean enoughmoney=true;
if(copper>gp)
enoughmoney=false;
else
gp-=copper*COPPER_VALUE;
System.out.println(copper);
System.out.println(gp);
return enoughmoney;
}
public boolean removePlat(double platinum)
{
boolean enoughmoney=true;
if(platinum>gp)
enoughmoney=false;
else
gp-=platinum*PLATINUM_VALUE;
return enoughmoney;
}
public double getValue()
{
double gp=(GOLD_VALUE*gold)+(SILVER_VALUE*silver)+(COPPER_VALUE*copper)+(PLATINUM_VALUE*platinum);
return gp;
}
public void printReport()
 
{
System.out.println("The purse now contains:");
 
System.out.println("\t" + platinum + " platinum pieces");
 
System.out.println("\t" + gold + " gold pieces");
 
System.out.println("\t" + silver + " silver pieces");
 
System.out.println("\t" + copper + " copper pieces");
 
System.out.println("\tAnd has a "+ this.getValue() + " GP value.");
}
public void buryPurse()
{
stringToFile(Double.toString(gp),"gold.txt");
stringToFile(Double.toString(gp),"silver.txt");
stringToFile(Double.toString(gp),"copper.txt");
stringToFile(Double.toString(gp),"platinum.txt");
}
public void digUpPurse()
{
//***THE PROBLEM IS HERE***
gp=Integer.getInteger(file2String("gold.txt"));
gp=Integer.getInteger(file2String("silver.txt"));
gp=Integer.getInteger(file2String("copper.txt"));
gp=Integer.getInteger(file2String("platinum.txt"));
//***THE PROBLEM IS HERE***
}
private void stringToFile( String content, String fileName )
{
    try
    {
        File file = new File( fileName );
 
        // if file doesnt exists, then create it
        if ( ! file.exists( ) )
        {
            file.createNewFile( );
        }
 
        FileWriter fw = new FileWriter( file.getAbsoluteFile( ) );
        BufferedWriter bw = new BufferedWriter( fw );
        bw.write( content );
        bw.close( );
        //System.out.println("Done writing to " + fileName); //For testing
    }
    catch( IOException e )
    {
System.out.println("Error: " + e);
e.printStackTrace( );
    }
} //End method stringToFile
public String file2String(String filename)
{
 
    try
    {
        FileReader fileReader = new FileReader(filename);
        String fileContents = "";
        int i ;
 
        while((i =  fileReader.read())!=-1)
        {
            char ch = (char)i;
            fileContents = fileContents + ch;
        }//end while
 
        //System.out.println(fileContents);
        return fileContents;
    }catch(Exception e)
    {
System.out.println("Error: " + e);
return "Error " + e;
    }//end catch
 
}//end file2String
}

And here's my test for it.

import javax.swing.JOptionPane;
public class PurseTest
{
    public static void main(String[] args)
    {
        String plusGold = JOptionPane.showInputDialog("Enter Gold to add");
        String plusSilver = JOptionPane.showInputDialog("Enter Silver to add");
        String plusCopper = JOptionPane.showInputDialog("Enter Copper to add");
        String plusPlatinum = JOptionPane.showInputDialog("Enter Platinum to add");
        Purse myPurse=new Purse();
        double gold = Integer.parseInt(plusGold);
        double silver = Integer.parseInt(plusSilver);
        double copper = Integer.parseInt(plusCopper);
        double platinum = Integer.parseInt(plusPlatinum);
        myPurse.addGold(gold);
        myPurse.addSilver(silver);
        myPurse.addCopper(copper);
        myPurse.addPlat(platinum);
        System.out.println("   ");
        System.out.println("The purse now contains:");
        System.out.println("\t" + platinum + " platinum pieces");
        System.out.println("\t" + gold + " gold pieces");
        System.out.println("\t" + silver + " silver pieces");
        System.out.println("\t" + copper + " copper pieces");
        System.out.println("\tAnd has a "+ myPurse.gp + " GP value.");
        String takeGold = JOptionPane.showInputDialog("Enter Gold to subtract");
        String takeSilver = JOptionPane.showInputDialog("Enter Silver to subtract");
        String takeCopper = JOptionPane.showInputDialog("Enter Copper to subtract");
        String takePlatinum = JOptionPane.showInputDialog("Enter Platinum to subtract");
        gold = Integer.parseInt(takeGold);
        silver = Integer.parseInt(takeSilver);
        copper = Integer.parseInt(takeCopper);
        platinum = Integer.parseInt(takePlatinum);
        myPurse.removeGold(gold);
        myPurse.removeSilver(silver);
        myPurse.removeCopper(copper);
        myPurse.removePlat(platinum);
        System.out.println("   ");
        System.out.println("The purse now contains:");
        System.out.println("\t" + platinum + " platinum pieces");
        System.out.println("\t" + gold + " gold pieces");
        System.out.println("\t" + silver + " silver pieces");
        System.out.println("\t" + copper + " copper pieces");
        System.out.println("\tAnd has a "+ myPurse.gp + " GP value.");
        System.out.println("   ");
        System.out.println("The purse will now be buried.");
        myPurse.buryPurse();
        System.out.println("The purse now contains:");
        System.out.println("\t" + platinum + " platinum pieces");
        System.out.println("\t" + gold + " gold pieces");
        System.out.println("\t" + silver + " silver pieces");
        System.out.println("\t" + copper + " copper pieces");
        System.out.println("\tAnd has a "+ myPurse.gp + " GP value.");
        System.out.println("The purse will now be unburied.");
        myPurse.digUpPurse();
        System.out.println("The purse now contains:");
        System.out.println("\t" + platinum + " platinum pieces");
        System.out.println("\t" + gold + " gold pieces");
        System.out.println("\t" + silver + " silver pieces");
        System.out.println("\t" + copper + " copper pieces");
        System.out.println("\tAnd has a "+ myPurse.gp + " GP value.");
    }//End main
}//end Purse Test

In the digUpPurse() method, it tells me

java.lang.NullPointerException
null

I have no idea what this means.

it won't let me subtract copper.

Can you post the output from the program that shows what you are talking about?

Add some println() statements that print out the values of the variables as they are used so that they can be copied from the console to post here.

completely ignoring my silver and copper subtraction.

Where does the program show a message like this:?
"Your purse now has xxxx copper."

Or for silver?

When I subtract them though, it ignores the silver and copper.

Can you post the program's output that shows what you are talking about?

I don't see where there are any println statements for silver or copper. Please post the current version of the code that has println statements for silver and copper and add show strong comments like:
//>>>>>>>>>>***** HERE is the println for silver <<<<<<<<<<<*****
to make it easy to find.

Print out the values of:
public static final double SILVER_VALUE = 1/10;
public static final double COPPER_VALUE = 1/100;

1/10 and 1/100

I only get 0 for some reason...

The reason is integer division: 2/10 = 0
vs float division: 2/10.0 = 0.2

What value is not being computed correctly?
Try debugging the code by adding some println() statements to print out the value of all the variables used in the computations so you can see what the computer is doing.

nothing happens.

What value is not being computed correctly?
Try debugging the code by adding some println() statements to print out the value of all the variables used in the computations so you can see what the computer is doing.

I don't see anywhere else I could add a println() statement and learn from it

Then you need to learn how to debug.
Print out the value of gp and silver at the start and end of the removeSilver() method.
Print out the value returned by removeSilver().

Can you post the code with the errors?
The println statements should be the first thing inside the method and at the end just before the return statement.
After the return is unreachable.

Print both gp and silver

What is printed out when the program is executed?

There is no need to print SILVER_VALUE.

What was the value returned by the removeSilver() method?

What are the names of the variables for the values that were printed? The println() statements need to label the print out so you can tell which is which:
System.out.println("an ID "+ theVariableHere); // change "an ID" to a unique name

What does the if statement do with those values?

--- Update ---

You forgot to answer this question:

What was the value returned by the removeSilver() method?

The removeSilver() method returns a boolean:

public boolean removeSilver(double silver)

What is the value of that boolean? What does it mean if true and if false?

300.0 is the silver I tried to remove and 100.0 is the GP I had before

What does the if statement in removeSilver() do with those values?