How to Convert String into BigInteger in Java

Introduction

Converting a String to a BigInteger in Java is a common task when dealing with large integers that exceed the range of primitive data types. BigInteger provides operations for arithmetic, comparison, and bit manipulation. This blog post will explore different methods to convert a String to a BigInteger in Java.

Table of Contents

1. Using BigInteger(String) Constructor
2. Handling NumberFormatException
3. Complete Example Program
4. Conclusion

1. Using BigInteger(String) Constructor

The simplest way to convert a String to a BigInteger is by using the BigInteger constructor that takes a String as an argument. This constructor provides exact conversion without loss of precision.

Example:

import java.math.BigInteger;

public class StringToBigInteger {
    public static void main(String[] args) {
        String strValue = "12345678901234567890";

        // Convert string to BigInteger using BigInteger constructor
        BigInteger bigIntegerValue = new BigInteger(strValue);

        System.out.println("String value: " + strValue);
        System.out.println("BigInteger value: " + bigIntegerValue);
    }
}

Output:

String value: 12345678901234567890
BigInteger value: 12345678901234567890

Explanation:

• new BigInteger(strValue) converts the string value to its BigInteger representation.

2. Handling NumberFormatException

The BigInteger constructor throws a NumberFormatException if the string does not represent a valid number. It is essential to handle this exception to ensure the robustness of your code.

Example:

import java.math.BigInteger;

public class StringToBigIntegerWithExceptionHandling {
    public static void main(String[] args) {
        String strValue = "12345678901234567890a"; // Invalid numeric string

        try {
            // Attempt to convert string to BigInteger
            BigInteger bigIntegerValue = new BigInteger(strValue);
            System.out.println("String value: " + strValue);
            System.out.println("BigInteger value: " + bigIntegerValue);
        } catch (NumberFormatException e) {
            System.out.println("Invalid string format for BigInteger: " + strValue);
        }
    }
}

Output:

Invalid string format for BigInteger: 12345678901234567890a

Explanation:

• A try-catch block is used to handle the NumberFormatException that occurs when the string cannot be parsed as a BigInteger.

3. Complete Example Program

Here is a complete program that demonstrates all the methods discussed above to convert a String to a BigInteger in Java.

Example Code:

import java.math.BigInteger;

public class StringToBigIntegerExample {
    public static void main(String[] args) {
        String strValue1 = "12345678901234567890";
        String strValue2 = "98765432109876543210";
        String strValue3 = "12345678901234567890a"; // Invalid numeric string

        // Using BigInteger(String) Constructor
        BigInteger bigIntegerValue1 = new BigInteger(strValue1);
        System.out.println("Using BigInteger(String) Constructor:");
        System.out.println("String value: " + strValue1);
        System.out.println("BigInteger value: " + bigIntegerValue1 + "\n");

        // Handling NumberFormatException
        try {
            BigInteger bigIntegerValue2 = new BigInteger(strValue3);
            System.out.println("Handling NumberFormatException:");
            System.out.println("String value: " + strValue3);
            System.out.println("BigInteger value: " + bigIntegerValue2 + "\n");
        } catch (NumberFormatException e) {
            System.out.println("Handling NumberFormatException:");
            System.out.println("Invalid string format for BigInteger: " + strValue3 + "\n");
        }

        // Using BigInteger with a valid numeric string
        BigInteger bigIntegerValue3 = new BigInteger(strValue2);
        System.out.println("Using BigInteger with a valid numeric string:");
        System.out.println("String value: " + strValue2);
        System.out.println("BigInteger value: " + bigIntegerValue3);
    }
}

Output:

Using BigInteger(String) Constructor:
String value: 12345678901234567890
BigInteger value: 12345678901234567890

Handling NumberFormatException:
Invalid string format for BigInteger: 12345678901234567890a

Using BigInteger with a valid numeric string:
String value: 98765432109876543210
BigInteger value: 98765432109876543210

4. Conclusion

Converting a String to a BigInteger in Java can be accomplished using the BigInteger constructor. It is essential to handle the NumberFormatException to ensure your code is robust and can handle invalid input gracefully. By understanding these different methods, you can choose the one that best fits your needs and coding style.

Happy coding!