# Java.math.BigInteger.modInverse() Method

## Description

The java.math.BigInteger.modInverse(BigInteger m) returns a BigInteger whose value is (this-1 mod m).

## Declaration

Following is the declaration for java.math.BigInteger.modInverse() method.

```public BigInteger modInverse(BigInteger m)
```

m − The modulus.

## Return Value

This method returns a BigInteger object whose value is this-1 mod m.

## Exception

ArithmeticException − If m ≤ 0, or this BigInteger has no multiplicative inverse mod m (that is, this BigInteger is not relatively prime to m).

## Example

The following example shows the usage of math.BigInteger.modInverse() method.

```package com.tutorialspoint;

import java.math.*;

public class BigIntegerDemo {

public static void main(String[] args) {

// create 3 BigInteger objects
BigInteger bi1, bi2, bi3;

// Two numbers are relatively prime if they have no
// common factors, other than 1.
bi1 = new BigInteger("7");
bi2 = new BigInteger("20");

// perform modInverse operation on bi1 using bi2
bi3 = bi1.modInverse(bi2);

String str = bi1 + "^-1 mod " + bi2 + " is " +bi3;

// print bi3 value
System.out.println( str );
}
}
```

Let us compile and run the above program, this will produce the following result −

```7^-1 mod 20 is 3
```

java_math_biginteger.htm