Introduction to Streams

Streams

Streams

Java 8 introduced streams, which can ve visualised as a pipeline through which data can pass through.

Streams comprise three parts.

Source
A number of Intermediate Operations
A Terminal Operation

Stream Parts.png

Consider the following example

package demo;

import java.util.stream.Stream;

public class App {

  public static void main( final String[] args ) {
    final int sum = Stream.of( "1", "2", "3", "4" )
      .mapToInt( Integer::parseInt )
      .filter( App::isEvenNumber )
      .map( App::doubleNumber )
      .sum();

    System.out.printf( "The sum is %d%n", sum );
  }

  private static int doubleNumber( final int number ) {
    return number * 2;
  }

  private static boolean isEvenNumber( final int number ) {
    return number % 2 == 0;
  }
}

The above example makes use of streams.

It starts with a source of Strings
```
Stream.of( "1", "2", "3", "4" )
```
Then performs several intermediate operations
1. Converts the String to int
```
  .mapToInt( Integer::parseInt )
```
2. Removes the odd numbers
```
  .filter( App::isEvenNumber )
```
3. Doubles the numbers
```
  map( App::doubleNumber )
```
Finally, it performs a terminal operation which sums all numbers
```
.sum()
```

Introduction to Streams

Table of contents

Streams