multiple lines of code in stream.forEach

Question

I have the following code for reading lines of a file:

String fileName = "dataset/ANC-all-count.txt";
Integer i=0;
//read file into stream, try-with-resources
try (Stream<String> stream = Files.lines(Paths.get(fileName), StandardCharsets.ISO_8859_1)) {

    stream.forEach(System.out::println);
    i++;

} catch (IOException e) {
    e.printStackTrace();
}
System.out.println("count is : "+i);

but the problem is I need to put i++ inside the following line:

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

So I want something like this:

stream.forEach(System.out::println; i++);

But it does not work this way so can anyone help how I can make it work?

Answer 1

There are two completely different things you should ask here:

a) how do I place multiple lines of code in stream.forEach()?

b) what should I do to count the number of lines in a Stream?

The question b) is answered already by other posters; on the other hand, the general question a) has a quite different answer:

use a (possibly multi-line) lambda expression or pass a reference to multi-line method.

In this particular case, you'd either declare i a field or use a counter/wrapper object instead of i.

For example, if you want to have multiple lines in forEach() explicitly, you can use

class Counter { // wrapper class
    private int count;
    public int getCount() { return count; }
    public void increaseCount() { count++; }
}

and then

Counter counter = new Counter();
lines.stream().forEach( e -> {
    System.out.println(e);
    counter.increaseCounter(); // or i++; if you decided i is worth being a field
} );

Another way to do it, this time hiding those multiple lines in a method:

class Counter { // wrapper class
    private int count;
    public int getCount() { return count; }
    public void increaseCount( Object o ) {
        System.out.println(o);
        count++;
    }
}

and then

Counter counter = new Counter();
lines.stream().forEach( counter::increaseCount );

or even

Counter counter = new Counter();
lines.stream().forEach( e -> counter.increaseCount(e) );

The second syntax comes in handy if you need a consumer having more than one parameter; the first syntax is still the shortest and simplest though.

Answer 2

The forEach method takes an instance of any class that implements Consumer. So here is an example of using a custom Consumer implementation that keeps up with the count. Later you can call getCount() on the Consumer implementation to get the count.

import java.util.ArrayList;
import java.util.List;
import java.util.function.Consumer;

public class ConsumerDemo {
    public static void main(String[] args) {
        List<String> lines = new ArrayList<String>();
        lines.add("line 1");
        lines.add("line 2");

        MyConsumer countingConsumer = new MyConsumer();
        lines.stream().forEach(countingConsumer);
        System.out.println("Count: " + countingConsumer.getCount());
    }

    private static class MyConsumer implements Consumer<String> {
        private int count;

        @Override
        public void accept(String t) {
            System.out.println(t);
            count++;
        }

        public int getCount() {
            return count;
        }
    }
}

Answer 3

Use peek() and count():

i = (int) stream.peek(System.out::println) 
                .count();