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.

• BigInteger Class tutorials
• Convert BigInteger to/from BigDecimal
• Convert BigDecimal to/from String
• BigInteger Divide example
• BigInteger Multiplication example
• Convert BigDecimal to float
• Convert BigDecimal to double
• Top 10 BigInteger Examples(/2018/09/best-10-javamathbiginteger-class.html)
• Rounding bigdecimal to 2 decimal places
• Check BigDecimal contains Zero or not
• Convert BigInteger to/from ByteArray

java.math.BigInteger Class

BigInteger is a class defined in java.math package. Integer class is a wrapper of primitive type int and defined in the java. lang package.

There is no automatic conversion of Biginteger to/from Integer or int. We have to write a code to do the conversion.

The code is straightforward.

Conversion of Integer to/from BigInteger is a day-to-day task for a java programmer.

A few days back I need to convert the BigInteger to Integer in my java project.

BigInteger will be used in arbitrary precession arithmetic calculations where the result value of these calculations is out of the range of values of all primitive numeric types.

For Example, if we assign the below value, the compiler will not compile and throws The literal 12456878999999 of type int is out of range

Integer intvalue=12456878999999  

In Java, the Integer type stores the numerical values between the range of 2 power 31 -1 -2 power 31 because int is preserved over 4 bytes.

Long type stores the numerical values between the range of 2 power 63 -1 -2 power 63. The reason is that long data is over 8 bytes.

For BigInteger to Integer Conversion, If biginteger is unable to convert into Integer type, the conversion gives unexpected values and loses data about the magnitude of BigInteger and returns a value with the opposite sign, If Integer type, For Integers, It returns the lowest 4 bytes values, for Long, it returns the lowest 8 bytes values.

We will see the conversion examples with explanations in the below section.

Convert Integer to BigInteger object in java with example

Conversion of integer or int to BigInteger is an easy task, many ways we can convert Integer to BigInteger in java.

Using String Conversion - First, convert Integer to String object using empty string concat or using toString() method. BigInteger provides Constructor for accepting 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  

It works as expected. It makes unnecessary String object creation for the conversion and it requires more CPU cycles for string conversion. It is not suggestible.

We will see another approach using the valueOf() method.
Using valueOf() method :

BigInteger class has valueOf() static factory method which takes long value as input parameter and returns BigInteger Object whose value is equal of the same specified type.
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  

Covert BigInteger to Integer object

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

the following is the syntax of the method

public int intValue()

No parameters required
Returns - 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 always not safe to convert BigInteger to Integer as this will give overflow errors Maximum and Minimum Integer values are

Integer.MAX_VALUE =  2147483647  
Integer.MIN_VALUE = -2147483648  

Note: If the BigInteger value is out of the range of Integer values. You will see Overflow values like Negative values.

Please comment if you have any questions.