## 1.概述

The standard deviation (symbol is sigma – σ) is the measure of the spread of the data around the mean.

In this short tutorial, we’ll see how to calculate the standard deviation in Java.

## 2.计算标准偏差

Standard deviation is computed using the formula square root of ( ∑ ( Xi – ų ) ^ 2 ) / N, where:

• ∑ is the sum of each element
• Xi is each element of the array
• ų is the mean of the elements of the array
• N is the number of elements

We can easily calculate the standard deviation with the help of Java’s Math class:

``````public static double calculateStandardDeviation(double[] array) {

// get the sum of array
double sum = 0.0;
for (double i : array) {
sum += i;
}

// get the mean of array
int length = array.length;
double mean = sum / length;

// calculate the standard deviation
double standardDeviation = 0.0;
for (double num : array) {
standardDeviation += Math.pow(num - mean, 2);
}

return Math.sqrt(standardDeviation / length);
}``````

Let’s test our methods:

``````double[] array = {25, 5, 45, 68, 61, 46, 24, 95};
System.out.println("List of elements: " + Arrays.toString(array));

double standardDeviation = calculateStandardDeviation(array);
System.out.format("Standard Deviation = %.6f", standardDeviation);``````

The result will look like this:

``````List of elements: [25.0, 5.0, 45.0, 68.0, 61.0, 46.0, 24.0, 95.0]
Standard Deviation = 26.732179``````

## 3.总结

In this quick tutorial, we’ve learned how to calculate the standard deviation in Java.

As always, the example code from this article can be found over on GitHub.