Java Stream Summary

Stream Concept

Sequence of elements
Supports sequential/parallel operations
Lazy evaluation

Example:

Stream<String> stream = Stream.of("a", "b", "c");
List<String> result = stream
  .map(String::toUpperCase)
  .collect(Collectors.toList());

Creating Streams

From Collection:

List<String> list = Arrays.asList("a", "b", "c");
Stream<String> stream = list.stream();

Static Factory Methods:

Stream<Integer> stream1 = Stream.of(1, 2, 3);
Stream<Integer> stream2 = Stream.iterate(0, n -> n + 1);
Stream<String> stream3 = Stream.generate(() -> "hello");

Stream Operations

Intermediate Operations:
- map: Transform elements
- filter: Select elements
- flatMap: One-to-many transformation
- sorted: Sort elements
- distinct: Remove duplicates
```
stream.filter(x -> x > 0)
     .map(x -> x * 2)
     .sorted()
```
Terminal Operations:
- collect: Accumulate elements
- forEach: Process elements
- reduce: Combine elements
- count: Count elements
```
int sum = stream.reduce(0, Integer::sum);
long count = stream.count();
```

Parallel Streams

Automatic parallelization
Use multiple threads

Example:

list.parallelStream()
    .filter(x -> x > 0)
    .map(x -> x * 2)
    .collect(Collectors.toList());

Stream Characteristics

Single use only
Lazy evaluation
Non-interference required
Stateless preferred

Example:

Stream<String> stream = list.stream();
stream.forEach(System.out::println);
stream.forEach(System.out::println);  // IllegalStateException

Best Practices

Use streams for data processing
Consider parallel streams for large datasets
Avoid stateful operations
Handle stream closure properly
Use appropriate collectors
Consider performance implications