# Guava - LongMath Class

LongMath provides utility methods on long.

## Class Declaration

Following is the declaration for com.google.common.math.LongMath class −

```@GwtCompatible(emulated = true)
public final class LongMath
extends Object
```

## Methods

Sr.No Method & Description
1

static long binomial(int n, int k)

Returns n choose k, also known as the binomial coefficient of n and k, or Long.MAX_VALUE if the result does not fit in a long.

2

static long checkedAdd(long a, long b)

Returns the sum of a and b, provided it does not overflow.

3

static long checkedMultiply(long a, long b)

Returns the product of a and b, provided it does not overflow.

4

static long checkedPow(long b, int k)

Returns the b to the kth power, provided it does not overflow.

5

static long checkedSubtract(long a, long b)

Returns the difference of a and b, provided it does not overflow.

6

static long divide(long p, long q, RoundingMode mode)

Returns the result of dividing p by q, rounding using the specified RoundingMode.

7

static long factorial(int n)

Returns n!, that is, the product of the first n positive integers, 1 if n == 0, or Long.MAX_VALUE if the result does not fit in a long.

8

static long gcd(long a, long b)

Returns the greatest common divisor of a, b.

9

static boolean isPowerOfTwo(long x)

Returns true if x represents a power of two.

10

static int log10(long x, RoundingMode mode)

Returns the base-10 logarithm of x, rounded according to the specified rounding mode.

11

static int log2(long x, RoundingMode mode)

Returns the base-2 logarithm of x, rounded according to the specified rounding mode.

12

static long mean(long x, long y)

Returns the arithmetic mean of x and y, rounded toward negative infinity.

13

static int mod(long x, int m)

Returns x mod m, a non-negative value less than m.

14

static long mod(long x, long m)

Returns x mod m, a non-negative value less than m.

15

static long pow(long b, int k)

Returns b to the kth power.

16

static long sqrt(long x, RoundingMode mode)

Returns the square root of x, rounded with the specified rounding mode.

## Methods Inherited

This class inherits methods from the following class −

• java.lang.Object

## Example of LongMath Class

Create the following java program using any editor of your choice in say C:/> Guava.

### GuavaTester.java

```import java.math.RoundingMode;

public class GuavaTester {

public static void main(String args[]) {
GuavaTester tester = new GuavaTester();
tester.testLongMath();
}

private void testLongMath() {
try {

} catch(ArithmeticException e) {
System.out.println("Error: " + e.getMessage());
}

System.out.println(LongMath.divide(100, 5, RoundingMode.UNNECESSARY));
try {
//exception will be thrown as 100 is not completely divisible by 3
// thus rounding is required, and RoundingMode is set as UNNESSARY
System.out.println(LongMath.divide(100, 3, RoundingMode.UNNECESSARY));

} catch(ArithmeticException e) {
System.out.println("Error: " + e.getMessage());
}

System.out.println("Log2(2): " + LongMath.log2(2, RoundingMode.HALF_EVEN));

System.out.println("Log10(10): " + LongMath.log10(10, RoundingMode.HALF_EVEN));

System.out.println("sqrt(100): " + LongMath.sqrt(LongMath.pow(10,2), RoundingMode.HALF_EVEN));

System.out.println("gcd(100,50): " + LongMath.gcd(100,50));

System.out.println("modulus(100,50): " + LongMath.mod(100,50));

System.out.println("factorial(5): " + LongMath.factorial(5));
}
}
```

## Verify the Result

Compile the class using javac compiler as follows −

```C:\Guava>javac GuavaTester.java
```

Now run the GuavaTester to see the result.

```C:\Guava>java GuavaTester
```

See the result.

```Error: overflow
20
Error: mode was UNNECESSARY, but rounding was necessary
Log2(2): 1
Log10(10): 1
sqrt(100): 10
gcd(100,50): 50
modulus(100,50): 0
factorial(5): 120
```
guava_math_utilities.htm