Convert Java Stream to Array
June 10, 2020
Stream into Array. The best way to convert is using Stream.toArray(IntFunction) method. In our examples we will convert Java Stream into Array in following ways.
1. We will use
Stream.toArray(IntFunction) which will return the array of the desired type.
2. Using
Stream.toArray() method which will return Object[] and then we change it into required datatype.
3. For integer stream we can use
IntStream.toArray() that will return int[]. In the same way we can use LongStream.toArray() to get long[] and DoubleStream.toArray() to get double[].
4. We can convert stream into list and then list into array. To convert stream into list we need to use
collect(Collectors.toList()) on the stream and to convert list into array we can use List.toArray method.
Contents
1. Using Stream.toArray(IntFunction)
ThetoArray(IntFunction) method returns an array containing the elements of this stream using the provided generator as IntFunction. This method is terminal operation.
A[] toArray(IntFunction<A[]> generator)
IntFunction which produces a new array of the desired type and the provided length.
Returns: The method returns an array consisting the elements of stream.
Throws: The method throws
ArrayStoreException if the runtime type of any element of this stream is not assignable to the runtime component type of the generated array.
Example-1:
In this example we will convert stream of string into array of string.
List<String> list = Arrays.asList("A", "B", "C", "D");
String[] strArray = list.stream().toArray(String[]::new);
for(String s : strArray) {
System.out.println(s);
}
IntFunction as generator in toArray method using method reference.
Now find the example with lambda expression.
String[] strArray = list.stream().toArray(size -> new String[size]);
StreamToStringArray.java
package com.concretepage;
import java.util.Arrays;
import java.util.List;
public class StreamToStringArray {
public static void main(String[] args) {
List<String> list = Arrays.asList("Krishna", "Mahesh", "Kush");
String[] strArray = list.stream()
.filter(e -> e.startsWith("K"))
.toArray(size -> new String[size]);
for(String s : strArray) {
System.out.println(s);
}
}
}
Krishna Kush
Example-2:
In this example we will convert stream of integer into array of integer.
StreamToIntegerArray.java
package com.concretepage;
import java.util.Arrays;
import java.util.List;
public class StreamToIntegerArray {
public static void main(String[] args) {
List<Integer> list = Arrays.asList(10, 20, 30, 40);
Integer[] intArray = list.stream()
.map(e -> e * 2)
.toArray(Integer[]::new);
for(Integer i : intArray) {
System.out.println(i);
}
}
}
In the above example we have used method reference. Now find the code with lambda expression.
List<Integer> list = Arrays.asList(10, 20, 30, 40); Integer[] intArray = list.stream() .map(e -> e * 2) .toArray(size -> new Integer[size]);
2. Using Stream.toArray()
ThetoArray() method returns an Object array containing the elements of this stream.
Object[] toArray()
Example-1: In this example we will convert a stream of string into array of string. We know that
toArray() returns Object[], so to convert it in our required datatype, we can use Arrays.copyOf method.
Object[] objArray = Stream.of("AA", "BB", "CC").toArray();
String[] stArray = Arrays.copyOf(objArray, objArray.length, String[].class);
for(String s : stArray) {
System.out.println(s);
}
Example-2: In this example we will convert stream of integer into array of integer.
Object[] objArray = Stream.of(10, 20, 30, 40).toArray();
Integer[] intArray = Arrays.copyOf(objArray, objArray.length, Integer[].class);
for(Integer i : intArray) {
System.out.println(i);
}
3. Using IntStream.toArray()
TheIntStream is the stream of int-valued elements. The IntStream.toArray() method converts stream of int values into the int array.
int[] toArray()
IntStream object in following ways.
1.
IntStream intStream = IntStream.of(1,2,3,4,5);
IntStream intStream = IntStream.rangeClosed(1, 5);
IntStream intStream = Stream.of(4,5,6,7,8).mapToInt(i -> i);
Now let us discuss some examples to use
IntStream.toArray() method.
Example-1:
int[] intArray = IntStream.of(10, 20, 30, 40).toArray();
for(Integer i : intArray) {
System.out.println(i);
}
Example-2:
int[] intArray = IntStream.rangeClosed(10, 15).toArray();
for(Integer i : intArray) {
System.out.println(i);
}
Example-3:
int[] intArray = Stream.of(3,4,5,6).mapToInt(i -> i * 2).toArray();
for(Integer i : intArray) {
System.out.println(i);
}
4. Using Collectors.toList()
We can convert stream into list and then convert list into array. To convert stream into list we need to usecollect(Collectors.toList()) on the stream. To convert list into array we can use List.toArray method.
StreamToListToArray.java
package com.concretepage;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class StreamToListToArray {
public static void main(String[] args) {
System.out.println("--- For String ---");
String[] ar = Stream.of("Java", "Angular", "Spring")
.collect(Collectors.toList())
.toArray(new String[0]);
for(String e : ar) {
System.out.println(e);
}
System.out.println("--- For Integer ---");
Integer[] intArray = Stream.of(15, 20, 30)
.map(e -> e * 2)
.collect(Collectors.toList())
.toArray(new Integer[0]);
for(Integer i : intArray) {
System.out.println(i);
}
}
}
--- For String --- Java Angular Spring --- For Integer --- 30 40 60
