How to convert BigInteger to/from Integer in java?

How to convert BigInteger to/from Integer in java?

In this blog post, We are going to learn How to Convert Integer/int from/to Biginteger with examples.

You can also check my previous posts on the BigInteger class in java.

java.math.BigInteger Class

The BigInteger class is defined in the java.math package, while the Integer class is a wrapper for the primitive type int and is defined in the java.lang package.

There is no automatic conversion between BigInteger and Integer or int. A code snippet must be implemented for the conversion.

The code for the conversion is straightforward.

Converting between Integer and BigInteger is a common task for Java programmers.

A few days ago, I needed to convert a BigInteger to an Integer in my Java project.

BigInteger is utilized in arbitrary precision arithmetic calculations where the result value exceeds the range of all primitive numeric types.

For example, if we assign the value below, the compiler will not compile and will throw an error: The literal 12456878999999 of type int is out of range.

Integer intvalue=12456878999999

In Java, the Integer type stores numerical values within the range of 2^31 - 1 to -2^31 because an int is represented using 4 bytes.

The Long type, on the other hand, stores values within the range of 2^63 - 1 to -2^63, as long data is represented using 8 bytes.

For BigInteger to Integer conversion, if the BigInteger cannot be converted into an Integer type, the conversion may yield unexpected values and lose data about the magnitude of the BigInteger. It returns a value with the opposite sign for Integer type. For integers, it returns the lowest 4-byte values, and for long, it returns the lowest 8-byte values.

Examples of conversion will be discussed in the following section.

Convert Integer to BigInteger Object in Java with Example

Converting an integer or int to a BigInteger is a straightforward task. There are various ways to do these in Java.

  • Using String Conversion First, convert the Integer to a String object using empty string concatenation or the toString() method. The BigInteger class provides a constructor that accepts string values.

    import java.math.BigInteger;

public class ConvertIntegerToBigIntegerUsingString {
    public static void main(String[] args) {
        Integer value = 1123;
        BigInteger bi = new BigInteger("" + value); // convert to String using empty string concat
        System.out.println(bi);
        BigInteger bi1 = new BigInteger(value.toString()); // convert to String using toString method
        System.out.println(bi1);
    }
}

    The output of the above code execution is

    1123
1123

    This approach, however, creates unnecessary String objects for the conversion, resulting in increased CPU cycles for string conversion, making it less desirable.

    Another approach is to use the valueOf() method.

  • Using valueOf() method :

    The BigInteger class has a valueOf() static factory method that takes a long value as an input parameter and returns a BigInteger object with the specified value.

    Syntax:

    public static BigInteger valueOf(long val)

    Here is an example

    import java.math.BigInteger;
public class ConvertIntegerToBigIntegerUsingString {
    public static void main(String[] args) {
        int integerMaximumValue = 123;
        BigInteger bigIntegerdemo = BigInteger.valueOf(integerMaximumValue);
        System.out.println(bigIntegerdemo);
    }
}

    The result of the above program execution is

    123

Convert BigInteger to Integer Object

The BigInteger class has an intValue() method that converts it to an Integer object.

The syntax of the method is as follows

public int intValue()

No parameters are required, and it returns an int from the BigInteger value.

import java.math.BigInteger;

public class ConvertBigIntegerToInteger {
    public static void main(String[] args) {
        BigInteger bigInteger = BigInteger.valueOf(6895); // BigInteger Object creation
        System.out.println(bigInteger.intValue()); // using intValue
    }
}

Output:

6895

It is not always safe to convert BigInteger to Integer as this may result in overflow errors. The maximum and minimum Integer values are:

Integer.MAX_VALUE =  2147483647
Integer.MIN_VALUE = -2147483648

Note: If the BigInteger value is outside the range of Integer values, overflow values like negative values will be observed.