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*Spring 5*modules in REST With Spring:

**1. Overview**

This is an introductory article on the *BigDecimal* & the *BigInteger* data types in the Java programming language.

In this write-up, we’ll show in what scenarios we can use these data types.

**2. ***BigDecimal*

*BigDecimal*

*BigDecimal *is **the preferred data type when writing code involving money**, financial transactions. Also, in situations where precision is a must, and we require a more granular control over rounding off our calculations.

*BigDecimal* is an immutable data type which provides us two essential features:

- The ability to specify the scale. The scale is the number of digits to the right of the decimal point.
- Providing control over rounding off digits by a rounding off method.

These features are catered to the custom requirements of the developer when writing code dealing with money.

A *BigDecimal* object can be created like so:

BigDecimal bigDecimal = new BigDecimal("81.9065");

or:

BigDecimal bigDecimal = BigDecimal.valueOf(81.9065);

An *enum RoundingMode *provides several rounding modes for the *BigDecimal* type:

: Rounding mode to round towards positive infinity**CEILING**: Rounding mode to round towards zero**DOWN**: Rounding mode to round towards negative infinity**FLOOR**: Rounding mode to round towards “nearest neighbor” unless both neighbors are equidistant, in which case round down**HALF_DOWN**: Rounding mode to round towards the “nearest neighbor” unless both neighbors are equidistant, in which case, round towards the even neighbor**HALF_EVEN**: Rounding mode to round towards “nearest neighbor” unless both neighbors are equidistant, in which case round up**HALF_UP**: Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary**UNNECESSARY**: Rounding mode to round away from zero**UP**

Let’s go through a scenario where we set scale & round off the tax values providing a *RoundingMode* parameter. Here we have two *BigDecimal* objects *serviceTax* with an initial value of *56.0084578639 *& *entertainmentTax* with an initial value of *23.00689.*

Since our precision for the currency is two digits after the decimal, we provide an argument *2* in the *setScale* method. The *setScale* method is used to set the scale for the tax amounts. Along with the set scale argument, rounding off arguments are provided which specify the rule for rounding off the digit:

BigDecimal serviceTax = new BigDecimal("56.0084578639"); serviceTax = serviceTax.setScale(2, RoundingMode.CEILING); BigDecimal entertainmentTax = new BigDecimal("23.00689"); entertainmentTax = entertainmentTax.setScale(2,RoundingMode.FLOOR);

On printing the *serviceTax* & the *entertainmentTax* values we see:

serviceTax: 56.01 entertainmentTax: 23.00

The *serviceTax* amount which was initially *56.0084578639 *has been rounded off to *56.01 *as per the arguments in the *setScale* method.

And the *entertainmentTax* which was originally *23.00689* has been rounded off to *23.00*.

*+ – ** and */* the core mathematical operators are not overloaded in the *BigDecimal* class. It has methods like *add(), multiply(), divide()* to perform math operations. So now, if we want to sum up *serviceTax* & the *entertainmentTax* to get the *totalTax* we have to use the *add()* method of the *BigDecimal* class:

BigDecimal totalTax = serviceTax.add(entertainmentTax);

The *totalTax* value we get is:

totalTax: 79.01

This pretty much covers the fundamentals of the *BigDecimal* data type. To learn further about the API, do visit the BigDecimal doc here.

**3. ***BigInteger*

*BigInteger*

*BigInteger* class in Java is required in mathematical operations where the integer value is large & using the *int* data type would cause an integer overflow.

** BigInteger is used in scenarios where an int just won’t work**. For instance, if we calculate the factorial of digit 50 it would come out to be

*30414093201713378043612608166064768844377641568960512000000000000.*This value is too big for an

*int*data type to handle & can only be stored in a

*BigInteger*variable.

Let’s assume a large numeric value to process, 8731409320171337804361260816606476. Let’s say this number represents the count of stars in our galaxy.

We will now check if this value can be stored in an *int* variable:

int numStars = 8731409320171337804361260816606476;

As soon as we do this, the compiler complains about it:

*“The literal 8731409320171337804361260816606476 of type int is out of range”.*

This means the *int* variable cannot store such a big number. To deal with these scenarios, Java has the *BigInteger* data type which facilitates storage of such large values.

A *BigInteger* object can be created as below:

BigInteger numStars = new BigInteger("8731409320171337804361260816606476");

Just like the *BigDecimal* class *BigInteger* is an immutable data type. Basic mathematical operators *+ – ** and */* are not overloaded.

We have to use methods like *add(), multiply(), divide()* to perform math operations.

As assumed above, the number of stars in our galaxy the Milky way is *8731409320171337804361260816606476. *

Suppose, there is another galaxy Andromeda which has 5379309320171337804361260816606476 stars in it.

Let’s add up the stars of these two galaxies to find out the total stars present.

BigInteger numStarsMilkyWay = new BigInteger("8731409320171337804361260816606476"); BigInteger numStarsAndromeda = new BigInteger("5379309320171337804361260816606476"); BigInteger totalStars = numStarsMilkyWay.add(numStarsAndromeda);

On printing the variable *totalStars:*

totalStars: 14110718640342675608722521633212952

This sums up the basics of the *BigInteger* class. Please refer the doc if you need to dig in further.

**4. Conclusion**

This quick tutorial demonstrated the scenarios where the *BigDecimal* & the *BigInteger* data-types would come in handy.

Please find the code for the tutorial over on GitHub.