Java 8: preferred way to count iterations of a lambda?

Question

I face the same problem often. I need to count the runs of a lambda for use outside the lambda.

E.g.:

myStream.stream().filter(...).forEa         


        

Answer 1

An enum can be used, too. Especially if you have more than one counter in an iteration:

import java.util.Arrays;

class LambdaCounter {

    enum CountOf {

        NO,
        OK,
        ERROR;

        private int count;

        // can be named inc(), instead of the Greek capital Delta,
        // which stands for the math increment operator '∆' 
        synchronized int Δ( final int... times ) {

            if ( times.length <= 0 )
                return ++count; // increase by 1

            return count += Arrays.stream( times ).sum(); // increase by arguments
        }

        // can be named val[ue](), instead of the Greek capital Xi,
        // which stands for the math identity operator '≡' 
        int Ξ() {
            return count;
        }
    }

    public static void main( final String[] args ) {

        Arrays.stream( new int[] { 1, 2, 3, 4, 5, 6, 7 } )
            .forEach( i -> {
                CountOf.NO.Δ();
                @SuppressWarnings( "unused" )
                final int LHS_DUMMY =
                    i % 2 == 0
                        ? CountOf.OK.Δ()
                        : CountOf.ERROR.Δ();
            } );
        System.out.printf( "No: %d, OK: %d, Error: %d, Error.inc(38): %d, Error.inc(4, 4): %d%n",
            CountOf.NO.Ξ(), CountOf.OK.Ξ(), CountOf.ERROR.Ξ(), CountOf.ERROR.Δ( 38 ), CountOf.ERROR.Δ( 4, 4 ) );

        // Output:
        // No: 7, OK: 3, Error: 4, Error.inc(38): 42, Error.inc(4, 4): 50
    }
}