With Jep 3, it is now possible to evaluate expressions using decimal arithmetic. This allows calculations to be performed with specified accuracy or even unlimited accuracy. If you are running into precision problems or already know that you will require the highest possible precision in your calculations, we recommend using this operation mode.
Rather than using the
double type to represent numbers,
is used. The
BigDecimal class is part of the Java API and is
contained in the
java.math package. For more information on this
class, please read the Sun
Javadocs for BigDecimal.
The difference in the accuracy is best shown through an example. When performing
multiplication of two numbers of the
10*0.09 evaluates as 0.8999999999999999.
But when performing the same calculation using decimal arithmetic with the
10*0.09 evaluates as 0.9.
Using Jep in BigDecimal mode is simple. Simply create a new Jep instance using the BigDecComponents with:
import com.singularsys.jep.bigDecimals.BigDecComponents; ... jep = new Jep(new BigDecComponents());
This initializes Jep with a special the BigDecNumberFactory, BigDecOperatorTable and BigDecFunctionTable. By default, the math context is set to unlimited precision. But you can also initialize the components with a different math context. For example, to use 32-bit precision numbers simply use
jep = new Jep(new BigDecComponents(MathContext.DECIMAL32));
For more information about MathContexts refer to the Sun MathContext Javadocs.
Guaranteeing precision unfortunately comes at the cost of more complex algorithms
for basic operators and functions. For this reason, some of the functions
and operators available for
double arithmetic are not available
in the BigDecimal mode.
The supported operators and functions are as follows:
+, -, *, /, ^ (power), % (modulus)
>, <, >=, <=, == (equals)
&& (and), || (or), ! (not)
Just like with Jep in standard mode, you can add your own custom functions.
By default BigDecimal and Strings cannot be used together but as of release 3.4 this can now be turned on. The following code switches on this facility and adds the standard string functions.
// Create the BigDecComponents BigDecComponents compSet = new BigDecComponents(MathContext.DECIMAL64,true); // Create a jep instance jep = new Jep(compSet); // Add the standard set of string functions jep.setComponent(new StringFunctionSet());
The above code will allow strings to be concatenated using '+' and compared using '==', '!=', '<', '<=', '>=', '>'. The StringFunctionSet allows the left, right, lower, upper, substring, len, mid, trim.