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# Calculating the Power of a Number in Java Without Using Math pow() Method

We need to calculate a number raised to the power of some other number without using the predefined function java.lang.Math.pow()

In Java, we can calculate the power of any number by :

1. Calculating the power of a number through while loop or for loop.
2. Calculating the power of a number by the divide and conquer method.

To calculate the power of any number, the base number and an exponent are required.

Prerequisite:

The basic understanding of Java arithmetic operators, data types, basic input/output and loop etc.

Example:

```Input : base = 3, exponent = 3
Output: 27

Input : base = 2, exponent = 4
Output: 16```

Implementation:

1. Using while loop: The base and power values have been assigned respective values. Now, the while Loop will keep multiplying result variable by base variable until the power becomes zero.

Below is the implementation of the problem statement using the while loop:

## Java

 `// Calculate the power of a number in Java using while loop``import` `java.io.*;` `public` `class` `JavaApplication1 {``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `base = ``3``, power = ``3``;``        ``int` `result = ``1``;``        ``// running loop while the power > 0``        ``while` `(power != ``0``) {``            ``result = result * base;``            ``// power will get reduced after``            ``// each multiplication``            ``power--;``        ``}``        ``System.out.println(``"Result =  "` `+ result);``    ``}``}`

Output

`Result =  27`

Time Complexity: O(N), where N is power.

2. Using for loop: The base and power values have been assigned respective values. Now, in the above program, we can use for loop instead of while loop.

Below is the implementation of the problem statement using the while loop:

## Java

 `// Calculate the power of a number in Java using for loop``import` `java.io.*;` `public` `class` `JavaApplication1 {``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `base = ``3``, power = ``3``;``        ``int` `result = ``1``;` `        ``for` `(power = ``3``; power != ``0``; power--) {``            ``result = result * base;``        ``}``        ``System.out.println(``"Result =  "` `+ result);``    ``}``}`

Output

`Result =  27`

Time Complexity: O(N), where N is power.

3. Using the Divide and conquer method: Above operation can be optimized to O(log N) by calculating power(base, exponent/2) only once and storing it.

## Java

 `// Calculate the power of a number``// in Java using Divide and Conquer``class` `GFG {` `    ``public` `static` `int` `power(``int` `x, ``int` `y)``    ``{``        ``int` `temp;``        ``if` `(y == ``0``)``            ``return` `1``;``        ``temp = power(x, y / ``2``);` `        ``if` `(y % ``2` `== ``0``)``            ``return` `temp * temp;``        ``else` `{``            ``if` `(y > ``0``)``                ``return` `x * temp * temp;``            ``else``                ``return` `(temp * temp) / x;``        ``}``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``int` `x = ``2``;``        ``int` `y = ``3``;``        ``System.out.println(power(x, y));``    ``}``}`

Output

`8`

Time Complexity: O(log N), where N is power.

Auxiliary Space: O(1) as it is using constant variables