Java stream - filter a list of odd/even numbers
PROBLEM
You’re writing a Java program and wish to filter out a list of integer numbers. Given a list of integers, you want to have a new list having only odd numbers.
solution
Use the stream API and the filter method. Let’s suppose the following list:
List<Integer> numbers = Arrays.asList(2,3,4,1,0,-2,-45,-70,80,99,45,87,33,91,22,16,73,40,93);
We would like to filter the numbers and get the odd numbers only. We know that odd numbers are not divisible by 2 so we will use that logic for filtering. In Java the remainder of a division is the %, so a number is odd when
number % 2 == 1
Putting it into the filter lambda method:
List<Integer> oddNumbers = numbers.stream()
.filter(number -> number % 2 == 1)
.collect(Collectors.toList());
Running it inside a main method and printing the result:
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class OddNumbers {
public static void main(String[] args) {
List<Integer> numbers = Arrays.asList(2,3,4,1,0,-2,-45,-70,80,99,45,87,33,91,22,16,73,40,93);
List<Integer> oddNumbers = numbers.stream()
.filter(number -> number % 2 == 1)
.collect(Collectors.toList());
System.out.println(oddNumbers);
}
}
output - odd numbers
[3,1,99,45,87,33,91,73,93]
Looks correct.
If we wanted to get the even numbers, simply we change the logic inside filter to check for 0 instead of 1
number % 2 == 0
List<Integer> evenNumbers = numbers.stream()
.filter(number -> number % 2 == 0)
.collect(Collectors.toList());
output - even numbers
[2,4,0,-2,-70,80,22,16,40]
conclusion
In this post, we saw how to simply filter a list of integer numbers to get only the even/ odd ones. You can check the full documentation of the Stream API.