IntStream mapToDouble() in Java

Last Updated : 06 Dec, 2018

IntStream mapToDouble() returns a DoubleStream consisting of the results of applying the given function to the elements of this stream.

Note : IntStream mapToDouble() is a intermediate operation. These operations are always lazy. Intermediate operations are invoked on a Stream instance and after they finish their processing, they give a Stream instance as output.
Syntax :

DoubleStream mapToDouble(IntToDoubleFunction mapper)

Parameters :

DoubleStream : A sequence of primitive double-valued elements. This is the double primitive specialization of Stream.
mapper : A stateless function to apply to each element.

Return Value : The function returns a DoubleStream consisting of the results of applying the given function to the elements of this stream.

Example 1 :

// Java code for DoubleStream mapToDouble 
// (IntToDoubleFunction mapper) 
import java.util.*; 
import java.util.stream.IntStream; 
import java.util.stream.DoubleStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating an IntStream 
        IntStream stream = IntStream.of(2, 4, 6, 8, 10); 
  
        // Using DoubleStream mapToLong(IntToDoubleFunction mapper) 
        // to return a DoubleStream consisting of the 
        // results of applying the given function to 
        // the elements of this stream. 
        DoubleStream stream1 = stream.mapToDouble(num -> (double)num); 
  
        // Displaying the elements in stream1 
        stream1.forEach(System.out::println); 
    } 
} 

Output :

2.0
4.0
6.0
8.0
10.0

Example 2 :

// Java code for DoubleStream mapToDouble 
// (IntToDoubleFunction mapper) 
import java.util.*; 
import java.util.stream.IntStream; 
import java.util.stream.DoubleStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating an IntStream 
        IntStream stream = IntStream.range(5, 10); 
  
        // Using DoubleStream mapToLong(IntToDoubleFunction mapper) 
        // to return a DoubleStream consisting of the 
        // results of applying the given function to 
        // the elements of this stream. 
        DoubleStream stream1 = stream.mapToDouble(num -> (double)num / 3); 
  
        // Displaying the elements in stream1 
        stream1.forEach(System.out::println); 
    } 
} 

Output :

1.6666666666666667
2.0
2.3333333333333335
2.6666666666666665
3.0

Example 3 :

// Java code for DoubleStream mapToDouble 
// (IntToDoubleFunction mapper) 
import java.util.*; 
import java.util.stream.IntStream; 
import java.util.stream.DoubleStream; 
  
class GFG { 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        // Creating an IntStream 
        IntStream stream = IntStream.range(5, 10); 
  
        // Using DoubleStream mapToLong(IntToDoubleFunction mapper) 
        // to return a DoubleStream consisting of the 
        // results of applying the given function to 
        // the elements of this stream. 
        DoubleStream stream1 = stream.mapToDouble(Math::sin); 
  
        // Displaying the elements in stream1 
        stream1.forEach(System.out::println); 
    } 
} 

Output :

-0.9589242746631385
-0.27941549819892586
0.6569865987187891
0.9893582466233818
0.4121184852417566

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