Functional Programming in Java 8 -- For Venkat

[Deepak Lal]

Hi Venkat,
It is nice to ask questions here

1. Is Functional Programming really necessary in Java 8?


2. Can you illustrate the advantages and pitfalls when coding in Java 8 using Functional Programming ?


3. Why do we need a transformation from old way of coding to Functional Programming ?


4. Can you illustrate Functional Programming in Java 8 with a working example. ?


Hope to win this book. !!


Regards
Deepak Lal

[Venkat Subramaniam]

Hi Deepak,


> 1. Is Functional Programming really necessary in Java 8?

I think so. We've been programming with imperative style for way too long in Java.
Declarative style, expressiveness are some of the things that attracted me to other languages in the first place.
It is nice that we can create code with some of those very capabilities in Java. Those of us using Java don't
have to be deprived of those features any more.

> 2. Can you illustrate the advantages and pitfalls when coding in Java 8 using Functional Programming ?

I have mentioned some advantages in other posts, I will mention some of the pitfalls here.

Java has predominantly been imperative, OO, mutable state (or shared mutable state). FP is declarative and favors immutability.
We should use extra caution not to mix mutability, shared state, and functional style. The language offers a thin layer of protection,
but it's not hard to breach that. As programmers we should refrain from that temptation to mix these paradigms in an unhealthy manner.

> 3. Why do we need a transformation from old way of coding to Functional Programming ?

I touched on some of these here: Why FP

>4. Can you illustrate Functional Programming in Java 8 with a working example. ?

There are several examples out there, instead of repeating it here, if you would, please take a look at one example here:
Presentation from SpringOne2GX on Java 8

Thanks,

Venkat

[Deepak Lal]

Dear Venkat,
Thanks for explanation of all above mentioned points.

Point 2 :Venkats comment :: Java has predominantly been imperative, OO, mutable state (or shared mutable state). FP is declarative and favors immutability.
We should use extra caution not to mix mutability, shared state, and functional style. The language offers a thin layer of protection,
but it's not hard to breach that. As programmers we should refrain from that temptation to mix these paradigms in an unhealthy manner.

We should use extra caution not to mix mutability, shared state, and functional style.-->Can you just give me a rough example on this statement


Regards,
Deepak Lal

[Venkat Subramaniam]

We should use extra caution not to mix mutability, shared state, and functional style.-->Can you just give me a rough example on this statement


Here's one example, I've seen beginners of FP do this:

    List<Integer> values = Arrays.asList(1, 2, 3, 4, 5, 6);
    List<Integer> doubled = new ArrayList<>();  
    
    values.forEach(e -> doubled.add(e * 2));
    System.out.println(doubled);

In the above code, from within the lamba expression we're mutating the ArrayList. This one is quite easy to fix.

    List<Integer> values = Arrays.asList(1, 2, 3, 4, 5, 6);
    List<Integer> doubled = 
      values.stream()
            .map(e -> e * 2)
            .collect(toList());
    //import static java.util.stream.Collectors.toList;
    
    System.out.println(doubled);

In general we should avoid the temptation to mutate a variable from within a lambda expression. In other words,
we want to keep the lambda pure - as functions with no side effects.

Hope this answer your question.

[Deepak Lal]

Dear Venkat,
Thank you for your explanation. Can i get to see such examples in your book http://www.amazon.com/gp/product/1937785467?tag=jranch-20

I would like to learn through Examples. rather than just reading a book for namesake.

Hope to win this book .

Regards
Deepak Lal

[Venkat Subramaniam]

Deepak Lal wrote:... Can i get to see such examples in your book

Yes and you may also download the code examples from Source code from the book.

[Deepak Lal]

Dear Venkat
Thanks for the Source code.
Keeping fingers crossed to own a copy of this book through Java Ranch Promotion.
Regards
Deepak Lal