Learn Java 8 streams with an example - print odd/even numbers from Array and List

Example 1: Java 8 program to print odd numbers from a List 

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

/*Java 8 Program to find Odd Numbers from a List*/
public class DriverClass {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.
                              asList(1, 4, 8, 40, 11, 22, 33, 99);
        List<Integer> oddNumbers = numbers.stream().
                                    filter(o -> o % 2 != 0).
                                     collect(Collectors.toList());
        System.out.println(oddNumbers);
    }
}

1. Initialize List using Arrays.asList() method. Java's built-in Arrays.asList() method converts an array into a list. This method takes an array as an argument and returns a List object.

2. Java List interface provides stream() method which returns a sequential Stream with list of Integer as its source.

3. The Java stream filter() method allows us to narrow down the stream elements based on a criterion. Here we separated the odd numbers from all other numbers.

4. Using collect() method we put all odd numbers to a list.


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Example 2: Java 8 program to print even numbers from a List 

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

/*Java 8 Program to find Even Numbers from a List*/
public class DriverClass {
    public static void main(String[] args) {
        List<Integer> numbers = Arrays.
                               asList(1, 4, 8, 40, 11, 22, 33, 99);
        List<Integer> evenNumbers = numbers.stream().
                                     filter(o -> o % 2 == 0).
                                      collect(Collectors.toList());
        System.out.println(evenNumbers);
    }
}

1. Initialize List using Arrays.asList() method. Java's built-in Arrays.asList() method converts an array into a list. This method takes an array as an argument and returns a List object.

2. Java List interface provides stream() method which returns a sequential Stream with list of Integer as its source.

3. The Java stream filter() method allows us to narrow down the stream elements based on a criterion. Here we separated the even numbers from all other numbers.

4. Using collect() method we put all even numbers to a list.



Example 3: Java 8 program to print even numbers from an array 

import java.util.Arrays;

/*Java 8 Program to find Even Numbers from an Array*/
public class DriverClass {
    public static void main(String[] args) {
        int[] numbers = {2, 5, 7, 8, 99, 1, 22, 4, 3, 77, 66};
        Arrays.stream(numbers).filter(o -> o % 2 == 0).
                              forEach(System.out::println);
    }
}

1. Arrays.stream() is used to get a sequential stream from the array passed as the parameter with its elements.

2. The Java stream filter() method allows us to narrow down the stream elements based on a criterion. Here we separated the even numbers from all other numbers.

3. forEach() is a terminal operation, that performs an action for each element of the stream. Here printing each element.


Example 4: Java 8 program to print odd numbers from an array 

import java.util.Arrays;

/*Java 8 Program to find Odd Numbers from an Array*/
public class DriverClass {
    public static void main(String[] args) {
        int[] numbers = {2, 5, 7, 8, 99, 1, 22, 4, 3, 77, 66};
        Arrays.stream(numbers).filter(o -> o % 2 != 0).
                                    forEach(System.out::println);
    }
}

1. Arrays.stream() is used to get a sequential stream from the array passed as the parameter with its elements.

2. The Java stream filter() method allows us to narrow down the stream elements based on a criterion. Here we separated the odd numbers from all other numbers.

3. forEach() is a terminal operation, that performs an action for each element of the stream. Here printing each element.


Example 5: Java 8 program to print odd numbers from a Set 

import java.util.Set;
import java.util.stream.Collectors;

/*Java 8 Program to find Odd Numbers from a set*/
public class DriverClass {
    public static void main(String[] args) {
        Set<Integer> numbers = Set.of(1, 4, 8, 40, 11, 22, 33, 99);
        Set<Integer> oddNumbers = numbers.stream().
                                   filter(o -> o % 2 != 0).
                                    collect(Collectors.toSet());
        System.out.println(oddNumbers);
    }
}

1. Created Immutable Set using Set.of() method

2. Java Set interface provides stream() method which returns a sequential Stream with set of Integer as its source.

3. The Java stream filter() method allows us to narrow down the stream elements based on a criterion. Here we separated the odd numbers from all other numbers.

4. Using collect() method we put all odd numbers to a Set.


Example 6: Java 8 program to print even numbers from a Set
import java.util.Set;
import java.util.stream.Collectors;

/*Java 8 Program to find even numbers from a set*/
public class DriverClass {
    public static void main(String[] args) {
        Set<Integer> numbers =Set.of(1, 4, 8, 40, 11, 22, 33, 99);
        Set<Integer> evenNumbers = numbers.stream().
                                    filter(o -> o % 2 == 0).
                                     collect(Collectors.toSet());
        System.out.println(evenNumbers);
    }
} 

1. Created Immutable Set using Set.of() method

2. Java Set interface provides stream() method which returns a sequential Stream with set of Integer as its source.

3. The Java stream filter() method allows us to narrow down the stream elements based on a criterion. Here we separated the even numbers from all other numbers.

4. Using collect() method we put all even numbers to a Set.


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