pyramid of numbers

[Campbell Ritchie]

Why have you marked all the methods static in the second version?
Why do your methods in the first version return this rather than an int[] or similar? If you are reading into a field of the current object, why not make the method void? There may be a good reason for returning this: you can write
myObject.foo(...).bar(...).baz(...).biz(...).buzz(...);
If you go through the API for StringBuilder you will see that is how must of its methods are designed.
I suggest you indent your Streams code differently:-

this.digits = Arrays.stream(stringDigits.split(""))
                    .mapToInt(Integer::parseInt)
                    .toArray();

You can replace the sort() call with this:-

this.digits = Arrays.stream(stringDigits.split(""))
                    .mapToInt(Integer::parseInt)
                    .sorted()
                    .toArray();

It is probably better to sort the IntStream in line 3 than the Stream<String> in line 2, otherwise "19" will come before "2".

For consecutive numbers, consider starting with the IntStream#range() and IntStream#rangeClosed() methods.

[am gueye]

I marked all the static methods in the second version to simplify the code.
In my first version, my methods return this because I wanted to write something like object.method1().method(). It was only for that.

Thanks for your suggestions, it makes the code clearer.    

[Knute Snortum]

sai rama krishna wrote:
i wonder why the method returns App like below

public App createArrayOfDigits()

It is so the methods can be chained together like this:

new App().readDigitsAsUserInput().createArrayOfDigits().displayPyramid();

[edit] Oops, didn't see that this had already been answered.

[sai rama krishna]

Saisir les chiffres: 1384
  1
 333
44444
8888888

i am able to see output.

I never saw a method returning its own class object? any other similar use cases or links or examples where method returns its own class object? it looks bit odd as i am familiar with returning String int etc mostly

[Knute Snortum]

sai rama krishna wrote:I never saw a method returning its own class object? any other similar use cases or links or examples where method returns its own class object? it looks bit odd as i am familiar with returning String int etc mostly

The builder pattern uses this technique.  I use this pattern a lot.  It's great for creating objects that have many fields or a lot of optional parameters.

[sai rama krishna]

sure. I will do that

 int[] digits = Arrays.stream(stringDigits.split("")).mapToInt(Integer::parseInt).toArray();

in above code what is ::

i never seen such operator? please advise

[sai rama krishna]

instead of  scanner.nextLine() can i use scanner.next()?
what is meaning of nextLine() method here?
i am entering input like
23192
etc in the same line right not next line?

[Campbell Ritchie]

The nextLine method returns from the current position of the cursor to the next instance of line end characters.
The next method returns the net token whether it is on the same line or not.
For the :: operator go through the Java™ Tutorials section and look for the part called method references.

[Knute Snortum]

Scanner#nextLine() returns everything up to and including the text separator.  Scanner#next() returns the next token.

In practical terms, next() is the missing nextString() function of Scanner -- with one limitation: it cannot return an empty String.  If you can live with that, only use next().  If you need to be able to get an empty String, things get complicated.