Converting BigDecimal to Integer

java

prompt-engineering

best-practices

autoboxing

byNikita Barsukov·Feb 3, 2025

Convert BigDecimal to Integer via intValue() for straightforward truncation:

BigDecimal bd = new BigDecimal("123.45");
Integer convertedInt = bd.intValue(); // Results in 123. Forget about the .45, like a broke shopping spree

Rounding can be performed by applying setScale(0, RoundingMode) before intValue():

Integer roundInt = bd.setScale(0, RoundingMode.HALF_UP).intValue(); // Rounds to 123, .45 just wasn't rounded enough

Beware: Surpassing the limits of Integer throws an ArithmeticException. Peekaboo with Integer.MAX_VALUE not advised!

Precision or truncation: Pick a side

When exact conversion is needed and you're a stickler for precision, use intValueExact() - will throw an exception if any fractional info goes bye-bye:

try {
    Integer exactInt = bd.intValueExact(); // Whines via an ArithmeticException if decimal part isn't zilch.
} catch (ArithmeticException e) {
    System.out.println("A fraction of truth was lost amid conversion.");
}

Java's autoboxing tango shows us it can convert int to Integer without breaking a sweat:

int nativeInt = bd.intValue(); // Like extra cheese on pizza, autoboxing has got this
Integer boxedInt = nativeInt;

Keeping the borders intact

Before you put the BigDecimal into an Integer, check if it fits in the box. In other words, ensure it's in Integer's field of PLAY – else, ArithmeticException sitting in the corner might jump you:

if (bd.compareTo(BigDecimal.valueOf(Integer.MAX_VALUE)) > 0 ||
    bd.compareTo(BigDecimal.valueOf(Integer.MIN_VALUE)) < 0) {
    throw new ArithmeticException("This BigDecimal says, 'Go Big or Go Home'");
}

Explicit instruction to Java to box comes in the form of Integer.valueOf():

Integer boxedInteger = Integer.valueOf(bd.intValue());

All the Java flavors and rounding modes

Yes, older Java had no intValueExact() for rounding. It went downhill for it with setScale():

Integer java7Int = bd.setScale(0, RoundingMode.DOWN).intValue();

Java 8 traded up with BigInteger for exact rounding.

Integer java8Int = bd.toBigInteger().intValueExact();

Traversing through possibilities

Edge cases of BigDecimal values severely larger than int demand robust exception handling:

try {
    Integer giganticInt = bd.toBigInteger().intValueExact();
} catch (ArithmeticException e) {
    // Too big for int to handle, must've been the extra decimals
}

Choosing between intValue() and intValueExact() is like choosing between walking on a tightrope or a highway - one provides no room for missteps:

// Walking on a tightrope
Integer riskyInt = bd.intValue();

// Safe walk on the highway
Integer safeInt;
try {
  safeInt = bd.intValueExact();
} catch (ArithmeticException e) {
  // Oops, fractional part or large value tripped us
}

Ensure your BigDecimal thinks small (within Integer.MAX_VALUE) before you pack it into an int:

if (bd.precision() - bd.scale() > 10) {
    throw new ArithmeticException("This BigDecimal lives the 'Go Big or Go Home' motto.");
}

In the nuttiest of shells - always test your conversions, remember biggies might change sign after conversion, and fractional parts could walk out, altogether.

It's all about the visual

Let's see visual aid for converting a BigDecimal to an Integer, representing these as a balloon and a bullseye respectively:

BigDecimal 🎈: [10.25]  
Landing Spot 🎯: [10]

The process of landing:

1️⃣ Jettison (setScale(0)) 🧳🛎️
2️⃣ Steady Glide (ROUND_DOWN or ROUND_UP) 🌬️🍃
3️⃣ Darts End Point (intValue) 🎯✅

Final Outcome

Journey from 🎈(BigDecimal) to 🎯(Integer): 
10.25 becomes 10 - bullseye!

The visual:

      /-🎈-\
     | 10.25 | ↘️  
      \---/      🌬️🛎️ (setScale to drop the decimal)
          |
          |         🍃 (ROUND_DOWN)
          |
        🎯10

A Jewelers' Guide on the Subject

BigDecimal (Java Platform SE 8) - Oracle laid out everything on BigDecimal.
The Numbers Classes - the Oracle again, this time showing how to make numbers work for you in Java.
java.math.BigDecimal#intValue - Program Creek, showing code examples of BigDecimal to Integer conversion.
BigDecimal Class in Java - GeeksforGeeks explaining the nooks and crannies of BigDecimal class.
Java division by zero doesn't throw an ArithmeticException - why? - A Stack Overflow convo, shedding light on BigDecimal's peculiarities.