Stream flatMapToLong(Function mapper) applies given mapper function to each element of a stream and returns a LongStream. Stream flatMapToLong(Function mapper) is an intermediate operation. Intermediate operations are invoked on a Stream instance and after they finish their processing, they give a Stream instance as output.
Note : Each mapped stream is closed after its contents have been placed into this stream. If a mapped stream is null, an empty stream is used, instead.
Syntax :
LongStream flatMapToLong(Function<? super T, ? extends LongStream> mapper) Where, LongStream is a sequence of primitive long-valued elements and T is the type of stream elements. mapper is a stateless function which is applied to each element and the function returns the new stream.
Example 1 : flatMapToLong() with operation of parsing string to long.
// Java code for Stream flatMapToLong // (Function mapper) to get an LongStream // consisting of the results of replacing // each element of this stream with the // contents of a mapped stream. import java.util.*;
import java.util.stream.LongStream;
class GFG {
// Driver code
public static void main(String[] args)
{
// Creating a list of Strings
List<String> list = Arrays.asList( "1" , "2" , "3" ,
"4" , "5" );
// Using Stream flatMapToLong(Function mapper)
list.stream().flatMapToLong(num ->
LongStream.of(Long.parseLong(num))).
forEach(System.out::println);
}
} |
Output :
1 2 3 4 5
Example 2 : flatMapToLong() with operation of mapping string with string length.
// Java code for Stream flatMapToLong // (Function mapper) to get an LongStream // consisting of the results of replacing // each element of this stream with the // contents of a mapped stream. import java.util.*;
import java.util.stream.LongStream;
class GFG {
// Driver code
public static void main(String[] args)
{
// Creating a List of Strings
List<String> list = Arrays.asList( "Geeks" , "GFG" ,
"GeeksforGeeks" , "gfg" );
// Using Stream flatMapToLong(Function mapper)
// to get length of all strings present in list
list.stream().flatMapToLong(str ->
LongStream.of(str.length())).
forEach(System.out::println);
}
} |
Output :
5 3 13 3
Example 3 : flatMapToLong() function with operation of returning stream.
// Java code for Stream mapToLong // (ToLongFunction mapper) to get a // LongStream by applying the given function // to the elements of this stream. import java.util.*;
import java.util.stream.LongStream;
class GFG {
// Driver code
public static void main(String[] args)
{
// Creating a list of Strings
List<String> list = Arrays.asList( "5.36" , "27.9" ,
"3" , "4.2" , "5" );
// Using Stream mapToLong(ToLongFunction mapper)
// and displaying the corresponding LongStream
list.stream().flatMapToLong(n
-> LongStream.of(Long.parseLong(n)) )
.forEach(System.out::println);
}
} |
Output :
Exception in thread "main" java.lang.NumberFormatException: For input string: "5.36"
Note : A Java NumberFormatException usually occurs when you try to do something like converting a String to a numeric value, like an int, float, double, long etc.