Thread: Code won't let me remove integer.

After I get this working, I plan to keep track of individual amounts of currency. For example, you won't be able to remove 400 silver if you only have 10 silver. But this is something I haven't really implemented yet.

I fixed the silver/copper problem, but now I have a new issue. I editted the code and original post.

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)
{
System.out.println(GOLD_VALUE);
System.out.println(SILVER_VALUE);
System.out.println(COPPER_VALUE);
System.out.println(PLATINUM_VALUE);
}
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.

"java.lang.NullPointerException
null"

Is all it gave me. Also, what's a stacktrace?