## Introduction

In Java, `DoubleStream` is a sequence of primitive double elements supporting sequential and parallel aggregate operations. It is part of the `java.util.stream` package and provides a convenient way to work with sequences of double values.

1. What is `DoubleStream`?
2. Creating a `DoubleStream`
3. Common Operations
4. Examples of `DoubleStream`
5. Real-World Use Case
6. Conclusion

## 1. What is DoubleStream?

`DoubleStream` is a specialized stream for working with double values, providing methods for processing elements, performing calculations, and generating statistics.

## 2. Creating a DoubleStream

You can create a `DoubleStream` in several ways:

• From an array: `DoubleStream.of(double... values)`
• Using `Arrays.stream(double[] array)`
• From a collection using `stream().mapToDouble()`
• Using `DoubleStream.generate()` or `DoubleStream.iterate()`

## 3. Common Operations

Some common operations on `DoubleStream` include:

• `filter()`: Filters elements based on a condition.
• `map()`: Transforms elements.
• `average()`: Calculates the average of the elements.
• `sum()`: Computes the sum of the elements.
• `min()`/`max()`: Finds the minimum or maximum element.
• `sorted()`: Sorts the elements.
• `forEach()`: Performs an action for each element.

## 4. Examples of DoubleStream

### Example 1: Creating and Summing a `DoubleStream`

This example demonstrates how to create a `DoubleStream` from a set of double values and calculate their sum.

``````import java.util.stream.DoubleStream;

public class SumExample {
public static void main(String[] args) {
double sum = DoubleStream.of(1.2, 2.5, 3.7)
.sum();
System.out.println("Sum: " + sum);
}
}
``````

Output:

``````Sum: 7.4
``````

### Example 2: Filtering and Averaging

In this example, we filter the stream to include only values greater than 2.0 and then calculate the average of the remaining values.

``````import java.util.OptionalDouble;
import java.util.stream.DoubleStream;

public class FilterAverageExample {
public static void main(String[] args) {
OptionalDouble average = DoubleStream.of(1.2, 2.5, 3.7, 4.1)
.filter(n -> n > 2.0)
.average();
System.out.println("Average: " + average.orElse(0.0));
}
}
``````

Output:

``````Average: 3.433333333333333
``````

### Example 3: Mapping and Sorting

This example shows how to map each element of a `DoubleStream` to its square and then sort the resulting values.

``````import java.util.stream.DoubleStream;

public class MapSortExample {
public static void main(String[] args) {
DoubleStream.of(1.2, 2.5, 3.7)
.map(n -> n * n)
.sorted()
.forEach(System.out::println);
}
}
``````

Output:

``````1.44
6.25
13.69
``````

## 5. Real-World Use Case: Calculating Standard Deviation

This example illustrates how to calculate the standard deviation of a set of double values using `DoubleStream`.

``````import java.util.stream.DoubleStream;

public class StandardDeviationExample {
public static void main(String[] args) {
double[] numbers = {1.2, 2.5, 3.7, 4.1};
double average = DoubleStream.of(numbers).average().orElse(0.0);
double variance = DoubleStream.of(numbers)
.map(n -> Math.pow(n - average, 2))
.average()
.orElse(0.0);
double stdDev = Math.sqrt(variance);
System.out.println("Standard Deviation: " + stdDev);
}
}
``````

Output:

``````Standard Deviation: 1.1078230586932
``````

## Conclusion

`DoubleStream` is used in Java for processing sequences of double values. It provides a range of operations for filtering, transforming, and aggregating data, making it particularly useful in numerical and scientific computations. Using `DoubleStream` can lead to cleaner and more efficient code, especially in data processing contexts.