Introduction to Streams

Input/Output and Streams in Java

Alex Liu

Software Development Engineer

Working with Streams

Java Streams
- Process data collections functionally and Improve performance for large data
- Supported Collections:
  - Lists (e.g. ArrayList, LinkedList)
  - Sets (e.g. HashSet, TreeSet)
  - Maps (Keys/Values as Streams) (e.g., HashMap, TreeMap)
  - Arrays (via Arrays.stream())
Example ArrayList named namesto use for the rest of the video
```
names: ["Alice", "Bob", "Charlie", "David"]
```

Using lambda expressions with Stream

Lambda Expressions
- Syntax: (parameters) -> { expression }

names.forEach(
    // `name` is a parameter representing each element in the list
    name -> 
        // This is the expression executed for each element.
        System.out.println(name));

Alice 
Bob 
Charlie 
David

Creating a Stream

Convert data collection to Stream
- Use .stream() on a collection
- Supports List, Set and Queue
Import Stream class
```
import java.util.stream.Stream;
```

Converted sample list names to streams and use .foreach() to access each element.

Stream<String> stream = names.stream();
stream.forEach(name -> System.out.println(name));

Filtering data with Streams

Use .filter() to select elements
- Keeps only matching elements

Converted sample list names to streams

Stream<String> stream = names.stream();

Use .filter() to match elements starts with A and use .forEach() to print them

stream
  .filter(name -> name.startsWith("A"))
  .forEach(name -> System.out.println(name));

Filter result: Alice

Counting elements with Streams

Use .count() to count elements
- Returns value in long format

Converted sample list names to streams

Stream<String> stream = names.stream();

Use .filter() to match elements starts with B and use .count() to count them

long count = names.stream()
  .filter(name -> name.startsWith("B"))
  .count();

Count result: 1 (only 1 element Bob start with B)

When to use Streams

When to Use Streams:
- For large datasets: Reduces performance overhead
- For functional operations: More readable than loops
- For filtering and transformations: Simplifies code
When NOT to Use Streams:
- For modifying original collections
- For simple loops with side effects

Let's practice!

Input/Output and Streams in Java