Lecture 13: Stream() Method Example

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The stream() method example problem statement

Implement the stream() method to print a list of integers.

The stream() method example solution

integers.stream().forEach(i -> System.out.print(i + " "));

The stream() method example output

6 7 8 9 10

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Hi there, My name is Marius from AlefTav Coding. Today, I will look at the two concepts stream() and lambda. In this lecture you will learn how to Implement the stream() method to print a list of integers.

stream() is a feature that was introduced in the Java 8 release in 2014. Because most Java programs have to process very large collections of data, the stream() feature was introduced to help deal with this. In fact, the main aim of stream() is to let you write code that can easily handle big collections.

import java.util.List;
public class Lecture13 {
    public static void main(String[] args) {
        List\<Integer\> integers = List.of(6, 7, 8, 9, 10);
        integers.stream()
                        .forEach(i -> System.out.print(i + “ ”) );
    }
}

Now, I will look at this solution implementation. Here, I have a collection of numbers named, integers. I want to be able to process this collection. So, I have to turn the collection into a stream. Technically, I am making a call to the stream() method with the code, dot stream(). The two round brackets after the word, stream indicate that I am working with a method.

Once my collection has been turned into a stream of values, I can then call certain specified methods. In this example, I am calling the method, forEach(), because I am going to process each value. In particular, I want to print each value, separated by a single space.

We say that forEach() calls a lambda to do this. This lambda code is read as follows. Given a value i, short for integer, return that value by printing it on the computer screen. And then add one space (+ " "). The lambda operator is a dash, followed by a greater than symbol (->).

If you do not understand this code at first, think it over and eventually it will begin to make sense.

My class in today's lesson is Lecture13. As always, with Java there must be a main(). Then, I am creating a collection to work with.

My data type is a general List with a sub-type Integer, between the angle brackets (< >). Note the capital letter, I in Integer. With a List, you have to use the non-primitive type, which all start with capital letters (Integer). I am using the Integer data type, because my values are discrete, whole numbers. I declare the list of values as integers, all small letters. Then, I assign the numbers by adding each of the numbers 6 to 10 to my list with the expression, List<Integer> integers = List.of(6, 7, 8, 9, 10);.

Then, just as with the Scanner class in a previous lecture, I will need to do an import. This time it is for, List (import java.util.List;).

With my program complete, I can run it. The output is as follows: the value, 6, followed by one space, followed by 7, one space till the value 10 and one space.

In this lecture you learnt how to implement a stream() and a lambda. These are two concepts you should try to understand thoroughly, because it will make your life as a java developer so much more pleasant. Now, as usual, I have here a coding exercise for you to practise your new-found skills.

stream() method coding exercise:
Implement the stream() method to print the names of the BRICS countries. (See below)

public class Lecture14 {
    public static void main(String[] args) {
        List<String> brics = List.of(
            “Brazil”, “Russia”,“India”, “China”, “South Africa”);
        // TODO: Implement the ‘stream()’  
    }
}

My name is Marius from AlefTav Coding. Till our next meeting, KEEP CODING.

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