Java : Streams and Lambda

The purpose of streams and lambda is to

Tell the computer "what to do" instead of "how to do".

Below is the example of looping over the colors traditionally.

 List<String> allColors = List.of("Red", "Blue", "Yellow");
    for (String color : allColors) {
    System.out.println();
}

Lambda

• an implementation of an interface with single abstract method (functional interface)

List allColors = List.of("Red", "Blue", "Yellow");
allColors.forEach(color -> System.out.printLn(color));

That reminds me of the arrow function in JavaScript

const allColors = ["Red", "Blue", "Yellow"];
allColors.forEach(color => {
    console.log(color);
});

Same result

Red
Blue
Yellow

Stream

• the collection of stream will be immutable
• the stream cannot be reused
• pipeline operation
  • source to get (.stream())
  • intermediate operation(.limit())
  • terminal operation(.collect())
  • need at least a source and a terminal operation

List<String> str = List.of("a", "b", "c");

// looping
str.stream().forEach(System.out::println);

// filtering
str.stream()
   .filter(s -> s.startsWith("a"))
   .forEach(System.out::println);

// uppercasing
str.stream()
   .map(String::toUpperCase)
   .forEach(System.out::println);

// checking
boolean allContainB = str.stream()
                        .allMatch(s -> s.contains("b"));
System.out.println("All contain 'b': " + allContainB);

Except above, there are many other terminal operations like: .count() .findFirst() to speed up and make the operation more concise and intuitive.