Java 8 : Streams

Its an layer / wrapper around collection, that enables declarative data processing like SQL. They can be sourced from Collections , Arrays . I/O.

Some characteristics include

1. Support pipeline operations : output of a stream operation can be another stream
2. Auto Iterations
3. Lazy Evaluation 
4. Automatic parallelization

Streams have 2 kinds of operations to it

1. Intermediate : they return one more stream
• filter
• map
• sorted
2. Terminal : they return a void or a non-stream
• forEach
• ifPresent

Most Stream operations accept lambda specifying exact behavior of operation.

With these inputs its easy to see how these code snippets would work

public static void method1() {
   Arrays.asList("alpha1", "alpha2", "alpha3")
     .stream()
     .findFirst()
     .ifPresent(System.out::println);  
}

Another Example

public static void method2() {
  List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
  List<String> filtered = strings.stream().filter(string -> !string.isEmpty()).collect(Collectors.toList());
  System.out.println(filtered);
}

Streams can be of two types

1. Sequential
2. Parallel : can be executed parallely without need to write MultiThreaded code.