Error With Big Decimal in Java

Question

I keep getting the

The method add(BigDecimal) in the type BigDecimal is not applicable for the arguments (pay)"

error with the code below.

For reference I have saved the pay class in a separate file, where I import BigDecimal as well.

Would one of you like to point out where I'm lacking/misunderstanding? I've tried to find a solution, but I couldn't find something.

import java.util.Scanner;
import java.math.BigDecimal;

class SalesPreInt { 
    public static void main(String[] args) {
        Pay pay = new Pay();
        pay.basePay();

        BigDecimal intCalc = new BigDecimal("0.15");

        Scanner userInput = new Scanner(System.in);

        System.out.println("What were your total sales?");
        BigDecimal salesPre = userInput.nextBigDecimal();
        System.out.println("You're Total Sales were "+salesPre);

        userInput.close();

        BigDecimal postIntCalc = salesPre.multiply(intCalc);
        BigDecimal salesCom = postIntCalc.add(salesPre);
        int finalCalc = salesCom.add(pay);

        System.out.println("Your total sales including commission is "+salesCom);
        System.out.println("Your total pay is"+finalCalc);
    }   
}

pay.java file below:

import java.math.BigDecimal;

public class Pay {
    public void basePay() {
        int basePay = 50000;
        BigDecimal bd = new BigDecimal(String.valueOf(basePay));
    }
}

Answer 1

Like the error message tells you, the add method of BigDecimal with one argument expects a BigDecimal instance: [javaDoc]

public BigDecimal add(BigDecimal augend)

Returns a BigDecimal whose value is (this + augend), and whose scale is max(this.scale(), augend.scale()).

Parameters:
augend - value to be added to this BigDecimal.

Returns:
this + augend

You've passed a variable of type Pay to this method and since Pay is not a subtype of BigDecimal it is not related to it. The method add can't know how to add a Pay instance, the compiler complains about that argument type.

You can do the following fix, to bypass that problem:

Your basePay method creates a BigDecimal and I guess this is the one you like to add to salesCom, so change that method a bit:

public BigDecimal basePay() {
    int basePay = 50000;
    return new BigDecimal(String.valueOf(basePay));
}

This method now creates a BigDecimal and returns it to the calling method. Now change the add method call to use the basePay method:

int finalCalc = salesCom.add(pay.basePay());

Now there is only one problem left. As you can see in the JavaDoc posted above, add returns a new BigDecimal instance, but you're assigning the returned value to the variable finalCalc, which is of type int. So we need to change it to BigDecimal:

BigDecimal finalCalc = salesCom.add(pay.basePay());

Now your code compiles and it should work as expected.

Answer 2

If you want the Pay class to return a basePay value, you need a proper method for that, ie a method that actually returns the value, ie not a void method.

public class Pay {
    private int basePay = 50000;

    public BigDecimal getBasepay() {
        // no need to pass via strings, BigDecimal has a constructor that takes an int value
        BigDecimal bd = new BigDecimal(basePay);
        return bd;
    }
}

which will be called like

int finalCalc = salesCom.add(pay.getBasepay()).intValue();

as you want to store the result as an integer, or

BigDecimal finalCalc = salesCom.add(pay.getBasepay());

Notice that I declared basePay - the value - as a private member of the Pay class, and renamed the method to start with get (called a getter in Java, and by convention their names are prefixed with get). If some day you need a way to modify that value, just add a setter

public void setBasepay(int bp) {
    basePay = bp;
}

And maybe you also want to be able to set the value directly as a BigDecimal although it's stored as an int? Just add

public void setBasepay(BigDecimal bp) {
    basePay = bp.intValue();
}

Two methods with the same name but other arguments is called overloading, and that's an often-used mechanism to introduce flexibility and versatility in your programs.

I would also suggest you have a look at a good tutorial, the official one by Oracle is pretty good (and free :))