The mapToDouble()
method in Java, part of the java.util.stream.LongStream
interface, is used to apply a given function to each element of the stream, producing a new DoubleStream
of the results. This method is useful when you need to transform the elements of a LongStream
into double
values.
Table of Contents
- Introduction
mapToDouble()
Method Syntax- Understanding
mapToDouble()
- Examples
- Basic Usage
- Using
mapToDouble()
with a Custom Function
- Real-World Use Case
- Conclusion
Introduction
The mapToDouble()
method transforms each element of a LongStream
by applying a specified function to it, resulting in a new DoubleStream
of transformed elements. This method is an intermediate operation, meaning it returns a new stream and does not modify the original stream.
mapToDouble() Method Syntax
The syntax for the mapToDouble()
method is as follows:
DoubleStream mapToDouble(LongToDoubleFunction mapper)
Parameters:
mapper
: ALongToDoubleFunction
that represents the function to be applied to each element of the stream.
Returns:
- A new
DoubleStream
consisting of the results of applying the given function to the elements of the original stream.
Throws:
- This method does not throw any exceptions.
Understanding mapToDouble()
The mapToDouble()
method allows you to transform each element of a LongStream
into a double
by applying a specified function to it. The resulting stream contains the transformed double
elements, each of which is the result of applying the function to the corresponding element in the original stream.
Examples
Basic Usage
To demonstrate the basic usage of mapToDouble()
, we will create a LongStream
and use mapToDouble()
to convert each element to its square root.
Example
import java.util.stream.DoubleStream;
import java.util.stream.LongStream;
public class MapToDoubleExample {
public static void main(String[] args) {
LongStream stream = LongStream.of(1L, 4L, 9L, 16L, 25L);
// Use mapToDouble() to compute the square root of each element
DoubleStream sqrtStream = stream.mapToDouble(Math::sqrt);
// Print the elements of the DoubleStream
sqrtStream.forEach(System.out::println);
}
}
Output:
1.0
2.0
3.0
4.0
5.0
Using mapToDouble()
with a Custom Function
This example shows how to use mapToDouble()
with a custom function to transform each element of the stream.
Example
import java.util.stream.DoubleStream;
import java.util.stream.LongStream;
public class MapToDoubleCustomFunctionExample {
public static void main(String[] args) {
LongStream stream = LongStream.of(10L, 20L, 30L, 40L, 50L);
// Use mapToDouble() with a custom function to convert each element to its half value
DoubleStream halfStream = stream.mapToDouble(n -> n / 2.0);
// Print the elements of the DoubleStream
halfStream.forEach(System.out::println);
}
}
Output:
5.0
10.0
15.0
20.0
25.0
Real-World Use Case
Converting Transaction Amounts to Dollars
In real-world applications, the mapToDouble()
method can be used to convert transaction amounts from one currency to another, such as converting cents to dollars.
Example
import java.util.stream.DoubleStream;
import java.util.stream.LongStream;
public class MapToDoubleTransactionsExample {
public static void main(String[] args) {
LongStream transactionAmountsInCents = LongStream.of(10000L, 20000L, 15000L, 30000L, 25000L);
// Use mapToDouble() to convert transaction amounts from cents to dollars
DoubleStream transactionAmountsInDollars = transactionAmountsInCents.mapToDouble(amount -> amount / 100.0);
// Print the transaction amounts in dollars
transactionAmountsInDollars.forEach(amount -> System.out.println("Transaction Amount: $" + amount));
}
}
Output:
Transaction Amount: $100.0
Transaction Amount: $200.0
Transaction Amount: $150.0
Transaction Amount: $300.0
Transaction Amount: $250.0
Conclusion
The LongStream.mapToDouble()
method is used to apply a given function to each element of the stream, producing a new DoubleStream
of the results. This method is particularly useful for transforming the elements of a LongStream
into double
values. By understanding and using this method, you can efficiently manage and process streams of values in your Java applications, ensuring that each element is transformed as needed.
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