Convert a String to a BigInteger in Java

In Java, the BigInteger class is a part of the java.math package and is designed to handle arbitrary precision integers. Unlike primitive data types such as int or long, which have fixed size limits, BigInteger can represent integers of any size, limited only by the available memory.

Example of String to BigInteger Conversion

Given a String, and converting it into BigInteger Number.

Example 1: Input String: “12345678901234578901201234567890”
Output BigInteger: 12345678901234578901201234567890

Example 2: Hexadecimal String: “1b4a5c6d7e8f”
Output BigInteger: 30006192209551

How to Convert a String to a BigInteger in Java?

There are certain methods to convert String to BigInteger in Java as mentioned below:

1. Using BigInteger(String) constructor
2. using valueOf() method

1. Convert String into BigInteger Using Constructor

Below is the implementation of the above method:

Java

// Java Program to implement
// Convert String to BigInteger
// Using BigInteger Constructor

import java.math.BigInteger;

// Driver Class
class GFG {
      // main function
    public static void main (String[] args) {
          // String Created
        String numberStr = "12345678901234578901201234567890";

          // Converted BigInteger
          BigInteger bigInt = new BigInteger(numberStr);

        System.out.println("String: " + numberStr);
        System.out.println("BigInteger: " + bigInt);
    }
}

Output

String: 12345678901234578901201234567890
BigInteger: 12345678901234578901201234567890

2. Convert using BigInteger.valueOf() method

Below is the implementation of BigInteger.valueOf() method:

Java

// Java Program to implement
// Convert String to BigInteger
// Using BigInteger Constructor
import java.io.*;
import java.math.BigInteger;

// Driver Class
class GFG {
      // main function
    public static void main(String[] args)
    {
          // String Declared
        String numberStr = "987654323245129963";

          // Converted to BigInteger using valueOf()
          BigInteger bigInt = BigInteger.valueOf(Long.parseLong(numberStr));

          // Result Displayed
        System.out.println("String: " + numberStr);
        System.out.println("BigInteger: " + bigInt);
    }
}

Output

String: 987654323245129963
BigInteger: 987654323245129963

Non-Decimal Integer Strings to BigInteger in Java

Similar to Decimal Number ( Number with Base 10 ) we can convert other number format like Base-2 (Binary), Base-8 (Octal) , Base-16(Hexadecimal) , etc.

Below is the implementation explaining the method for doing this conversion:

Java

// Java Program to implement Convert
// Non Decimal String to BigInteger
import java.io.*;
import java.math.BigInteger;

// Driver Class
class GFG {
      // main function
    public static void main(String[] args)
    {
        // Replace this string with your Hexadecimal bigInteger
        String hexString = "1b4a5c6d7e8f";

        // Convert Hexadecimal string to BigInteger
        BigInteger bigInt
            = new BigInteger(hexString, 16);

        // Print the result
        System.out.println("Hexadecimal String: " + hexString);
        System.out.println("Equivalent BigInteger: " + bigInt);
    }
}

Output

Hexadecimal String: 1b4a5c6d7e8f
Equivalent BigInteger: 30006192209551

Explaination of the above Program:

In the above example we are using BigInteger constructor to convert a string hexString which contain a String Number of Base 16. It explain the fact that if we want to convert string str with base x then we can use the syntax BigInteger res = new BigInteger( str, x );