Java Convert BigDecimal to BigInteger

In this Java core tutorial we learn how to convert a java.math.BigDecimal object to a java.math.BigInteger object in Java programming language.

How to convert BigDecimal to BigInteger in Java

In Java with a given BigDecimal value we can use the BigDecimal.toBigInteger() method to convert it to a BigInteger value as the following Java program.

ConvertBigDecimalToBigIntegerExample1.java

import java.math.BigDecimal;
import java.math.BigInteger;

public class ConvertBigDecimalToBigIntegerExample1 {
    public static void main(String... args) {
        BigDecimal bigDecimal = new BigDecimal("123456.999");

        BigInteger bigInteger = bigDecimal.toBigInteger();

        System.out.println("BigDecimal: " + bigDecimal);
        System.out.println("BigInteger: " + bigInteger);
    }
}

The output as below.

BigDecimal: 123456.999
BigInteger: 123456

We can also use the BigDecimal.toBigIntegerExact() method to convert a BigDecimal object to BigInteger object with an exception thrown if the BigDecimal value has nonzero factional part.

ConvertBigDecimalToBigIntegerExample2.java

import java.math.BigDecimal;
import java.math.BigInteger;

public class ConvertBigDecimalToBigIntegerExample2 {
    public static void main(String... args) {
        BigDecimal bigDecimal = new BigDecimal("99999999");

        BigInteger bigInteger = bigDecimal.toBigIntegerExact();

        System.out.println("BigDecimal: " + bigDecimal);
        System.out.println("BigInteger: " + bigInteger);
    }
}

The output as below.

BigDecimal: 99999999
BigInteger: 99999999

The example Java code below to show the BigDecimal value which throw a java.lang.ArithmeticException exception when we use the toBigIntegerExact() method to convert it.

ConvertBigDecimalToBigIntegerExample3.java

import java.math.BigDecimal;
import java.math.BigInteger;

public class ConvertBigDecimalToBigIntegerExample3 {
    public static void main(String... args) {
        BigDecimal bigDecimal = new BigDecimal("1.2");

        BigInteger bigInteger = bigDecimal.toBigIntegerExact();
    }
}

The output as below.

Exception in thread "main" java.lang.ArithmeticException: Rounding necessary
	at java.base/java.math.BigDecimal.commonNeedIncrement(BigDecimal.java:4628)
	at java.base/java.math.BigDecimal.needIncrement(BigDecimal.java:4684)
	at java.base/java.math.BigDecimal.divideAndRound(BigDecimal.java:4592)
	at java.base/java.math.BigDecimal.setScale(BigDecimal.java:2892)
	at java.base/java.math.BigDecimal.toBigIntegerExact(BigDecimal.java:3488)
	at ConvertBigDecimalToBigIntegerExample3.main(ConvertBigDecimalToBigIntegerExample3.java:8)

Happy Coding 😊

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