CODEWITHSUNDEEP
javalambdajava-8java-stream
Don Giulio
Don Giulio

Reputation: 3294

use Generator for generating Tuples in java

I'm trying to get grips on the new java8 streams.

I need to generate an infinite stream of tuples with certain characteristics:

The tuples will have three int values, a, b and c.

where b and c are simply counters, that could be made in a for loop with: 

for (int c = 1;; c++) {
    for (int b = 1; b < c; b++) {
        ...
    }
}

I would then use a filter to calculate a

I created a TupleFactory: 

class TupleFactory {
    private static int b = 1;
    private static int c = 1;

    public static Tuple next(){
        if (b >= c - 1)
            c++;
        else
            b++;
        return new MyTuple (1,b,c);
    }
}

and then I would like to generate the Stream<Tuple> with: 

Supplier<Tuple> anyTuple = s -> TupleFactory.next();
Stream<Tuple> result = Stream.generate(anyTuple);

I get a:

Lambda expression's signature does not match the signature of the functional interface method get()

in the line where I define the supplier...

any clues?

Upvotes: 1

Views: 602

Answers (2)

Pshemo
Pshemo

Reputation: 124265

Your lambda must provide body for 

T get();

method in Supplier<T> interface and handle all this method arguments. But in this case get method doesn't have any arguments so there is no need for s in s -> .... Instead of 

Supplier<Tuple> anyTuple = s -> TupleFactory.next();

use

Supplier<Tuple> anyTuple = () -> TupleFactory.next();
//                         ^^ - means no arguments

or maybe simpler use method references

Supplier<Tuple> anyTuple = TupleFactory::next;

Upvotes: 0

Mike Nakis
Mike Nakis

Reputation: 62054

First, get rid of every instance of static in your TupleFactory. That use of static is nonsense.

Then, try this:

TupleFactory myFactory = new TupleFactory();
Supplier<Tuple> anyTuple = myFactory::next;

If you don't want to fix your statics, then this should work:

Supplier<Tuple> anyTuple = TupleFactory::next;

Upvotes: 2

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