Intermediate operations Terminal operations

Description

A stream supports two types of operations:

• Intermediate operations
• Terminal operations

Intermediate operations are also called lazy operations.

Terminal operations are also called eager operations.

A lazy operation does not process the elements until an eager operation is called on the stream.

An intermediate operation on a stream produces another stream.

Streams link operations to create a stream pipeline.

Example

In the following code filter() and map() are all lazy operations. While reduce() is eager operation.

import java.util.Arrays;
import java.util.List;
//from  ww  w . j  a  v a2s.  com
public class Main {
  public static void main(String[] args) {
    List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
    int sum = numbers.parallelStream()
        .filter(n -> n % 2  == 1)
        .map(n  -> n * n)
        .reduce(0, Integer::sum);

    System.out.println(sum);
  }
}

The code above generates the following result.