Why list of String has no forEach method?

Question

I have problem with understand why String[] args variable has no forEach method? I can not find any information that this type is not Serializable or Collection because forEach methos implements Serializable.

For example, I have simple main Java class. If I want to use forEach method, I have to first import Arrays class and then on stream use forEach method like below:

import java.util.Arrays;

public class MyClass {
  public static void main(String[] args) {
    Arrays.stream(args).forEach(System.out::println);
  }
}

Why it is not possible to make it just simple like this?

args.forEach(System.out::println);

Answer 1

Short answer: Arrays don't have a forEach method defined on them.

Longer answer: Because it doesn't need it. An array type (using [], not List<>) represents a low level structure in memory, more suited to low level optimisations rather than higher level functional-style code. The hardware of a machine much more closely resembles the imperative, stateful style from languages like C, rather than the functional stateless style from languages like Haskell. Because of this, when creating a lower level data structure like a basic array, it doesn't necessarily make sense to give it more advanced functionality. If you really want a forEach() method, trivially wrap it using Arrays.asList(), Arrays.stream(), or List.of() (depending on Java version).

Answer 2

The main method takes one parameter of type String[]. Which is an Array of Strings.

Lists and Arrays are two different things and only the former does provide a foreach method.

Answer 3

Not just String array, Array of any object or primitive types do not have this feature since arrays are the data stricture that is different from other collection implementations

Answer 4

1. The direct superclass of an array type is Object.
2. Every array type implements the interfaces Cloneable and java.io.Serializable.

https://docs.oracle.com/javase/specs/jls/se7/html/jls-10.html

Any array type doesn't define forEach.

Why?

It simply wasn't implemented and the authors apparently want to keep array types as fundamentally pure as possible.

I don't think this method would be superfluous; on the contrary, I am sure it would be very handy. It's not a trivial task, though. Think about primitive arrays and how you would implement, let's say, a boolean consumer. You would have to bound a plain JDK class BooleanConsumer to a fundamental JVM concept boolean[], or to grand the interface a special status, or to generate the interface on the fly.