Re: java package - money
You should fix your newsgroup client so that you only post the same message
once, not eight times.
java_nut wrote:
good evening guys,
i am finding a piece of work extremely tough going at the moment and
wondered if i could get any hints/help on where im going wrong. i am
aiming to produce a package (money.java) which could be used in order
to produce arithmetic calculations on sums of money.
The code i have at the moment is:
MONEY.JAVA:
Upper- and lower-case matter. The class should be called "Money", not
"money", so the file should be "Money.java", not "MONEY.JAVA".
package java;
You are not permitted to define classes in the 'java' or 'javax' packages. It
is against the license that lets you use the Java(tm) language. Also, the
package name will correspond to a subdirectory name of the source code.
public class money
By convention, class names should begin with an uppercase letter: "Money"
rather than "money".
{
private int data1, data2;
Why two data values? How do you intend to use these?
Pick more meaningful names.
public money()
{
data1=0;
data2=0;
Java initializes instance variables to zero or the equivalent anyway, so this
initialization is redundant.
}
public money(int value1, int value 2)
{
data1 = value1;
data2 = value2;
}
public void addMoney(int value1, int value2)
{
return value1 + value2;
It looks like you never use data1 or data2. Why are they in the class?
You don't really need to repeat the word "Money" in the method names, since
the methods are specific to the "Money" clss anyway.
}
public void subtractMoney(int value1, int value2)
{
return value1 - value2;
}
public void divideMoney(int value1, int value2)
{
return value1 / value2;
}
What would you like the result to be if you divide "66 /100"?
public void multiplyMoney(int value1, int value2)
{
return value1 * value2;
}
}
MONEYTEST.JAVA
import java.money;
By convention, packages are based on your domain name. You are not permitted
to use "java" or "javax" as a package part in any published Java(tm) code,
unless you are Sun. Read the license that lets you use the language.
You are advised not to use "com.lewscanon" unless you are me.
If you had a domain "foo.com", your package would be something like
"com.foo.money". If you don't have a domain, or don't want to use one, just
use "money":
import money;
public class MoneyTest
{
public static void main(String [] args)
{
money p = new money(10,20);
System.out.println("The total is " + p.addMoney());
Did you actually try compiling this class? You didn't define an "addMoney()"
method, only an "addMoney( int, int )" method.
What if someone wanted to add three values? Divide? Negate?
You should test all your methods, not just one. Test all significant cases,
e.g., division of a large amount by a small one and vice versa. Division of
zero or by zero. Think about so-called "corner cases": those boundary
scenarios that can make life unpleasantly interesting if not handled properly.
}
}
I think i may need a 'toString' method?
Why?
Would you want to format it?
Take a look at
http://java.sun.com/j2se/1.5.0/docs/api/java/text/DecimalFormat.html
What about equals() and hashCode()? These are practically the first methods
you should consider overriding.
> and also, is there any way of covering errors?
First, eliminate the compilation errors. One of them was already pointed out
by another respondent.
Your methods provide no advantage or difference over the conventional int
operations.
int is probably too small a type for money anyway. A better choice might be
java.math.BigInteger, which already has the necessary methods defined to
handle many calculations. java.math.BigDecimal is also a good choice. Of
course, these might not be so good if you are calculating compound interest.
Note: both these classes are immutable. Immutable classes are very often a
Good Thing. Your Money class most likely should be immutable, assuming you
don't decide that BigInteger has everything in it already that you want.
How much money we talking 'bout, anyway?
- Lew