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# JDK 8 BigInteger Exact Narrowing Conversion Methods

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# JDK 8 BigInteger Exact Narrowing Conversion Methods

### When it comes to performing a narrowing conversion using BigInteger in Java 8, here is some information that made this process a lot easier.

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In the blog post, "Exact Conversion of Long to Int in Java," I discussed using Math.toIntExact(Long) to convert a `Long` to an `int` , using an ArithmeticException if this narrowing conversion is not possible. That method was introduced with JDK 8, which also introduced similar narrowing conversion methods to the BigInteger class. Those `BigInteger` methods are the topics of this post.

`BigInteger` had four new "exact" methods added to it in JDK 8:

• byteValueExact() — Converts `BigInteger` value exactly to `byte` if possible
• shortValueExact() — Converts `BigInteger` value to `short` if possible
• intValueExact() — Converts `BigInteger` value exactly to `int` if possible
• longValueExact() — Converts `BigInteger` value exactly to `long` if possible

As described above, each of these four "exact" methods added to `BigInteger` with JDK 8 allow for the `BigInteger`'s value to be narrowed to the data type in the method name, if that is possible. Because all of these types ( `byte`, `short`, `int`, and `long`) have smaller ranges than `BigInteger`, it's possible for any of these cases to have a value in `BigDecimal` with a magnitude larger than that which can be represented by any of these four types. In such a case, all four of these "Exact" methods throw an `ArithmeticException` , rather than quietly "forcing" the bigger value into the smaller representation, which is typically a nonsensical number for most contexts.

Examples of using these methods can be found on GitHub. When those examples are executed, the output looks like this:

``````
===== Byte =====
125 => 125
126 => 126
127 => 127
128 => java.lang.ArithmeticException: BigInteger out of byte range
129 => java.lang.ArithmeticException: BigInteger out of byte range
===== Short =====
32765 => 32765
32766 => 32766
32767 => 32767
32768 => java.lang.ArithmeticException: BigInteger out of short range
32769 => java.lang.ArithmeticException: BigInteger out of short range
===== Int =====
2147483645 => 2147483645
2147483646 => 2147483646
2147483647 => 2147483647
2147483648 => java.lang.ArithmeticException: BigInteger out of int range
2147483649 => java.lang.ArithmeticException: BigInteger out of int range
===== Long =====
9223372036854775805 => 9223372036854775805
9223372036854775806 => 9223372036854775806
9223372036854775807 => 9223372036854775807
9223372036854775808 => java.lang.ArithmeticException: BigInteger out of long range
9223372036854775809 => java.lang.ArithmeticException: BigInteger out of long range
``````

The addition of these "exact" methods to `BigInteger` with JDK 8 is a great addition, because errors associated with numeric narrowing and overflow have been subtle. It's nice to have an easy way to get an "exact" narrowing or to at least have the inability to do narrowing made obvious via an exception.

Topics:
java ,java 8 ,conversion ,biginteger ,integer ,long ,code ,how-to

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