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Henri Idrovo
Henri Idrovo

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Java 8 Stream API on Arrays

#java #stream #functional

Java 8 introduced the concept of functional programming. My first instinct when I need to iterate is to use a for-loop. So here are some common operations on arrays using the stream api. I'll reference this post when I need a friendly reminder. USE MORE STREAMS! You can read more about java streams here. Also I'm using the Java 8 method reference syntax, you can read more about that topic here.

Given an array of strings that represent a phone number, format and print each to console. 

String[] phoneNumbers = new String[] {"3125550909", "3125557676", "3125552323", "3125556161", "3125554141"}; String[] formattedPhoneNumbers = Arrays.stream(phoneNumbers) .map(value -> String.format("1-(%s)-%s-%s", value.substring(0,3), value.substring(3,6), value.substring(6,10))) .toArray(String[]::new); Arrays.stream(formattedPhoneNumbers).forEach(System.out::println);
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Given an array of strings that represent zip codes, filter out unwanted zip codes and print remaining to console. 

String[] zipCodes = new String[] {"60640","94102", "60602", "94115", "60647", "94140"}; String[] subsetZipCodes = Arrays.stream(zipCodes) .filter(value -> value.contains("606")) .toArray(String[]::new); Arrays.stream(subsetZipCodes).forEach(System.out::println);
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Given an array of sentences, count the number of occurrences for each word and print to console. 

String[] lines = new String[] { "toast for breakfast ", "sleepy in chicago", "tired in the morning", "coffee in the morning", "sleepy breakfast today", "breakfast in chicago" }; Map <String, Integer > wordCount = Arrays.stream(lines) .map(w -> w.split("\\s+")) .flatMap(Arrays::stream) .collect(Collectors.toMap(w -> w, w -> 1, Integer::sum)); wordCount.forEach((k, v) -> System.out.println(String.format("%s ==>> %d", k, v)));
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Given an array of names, and a custom NbaPlayer class, create a new array with elements of NbaPlayer type. 

String[] names = {"lebron", "kyrie", "doncic", "davis", "lavine"}; class NbaPlayer { String name; NbaPlayer(String name){ this.name = name; } @Override public String toString() { return "NbaPlayer{" + "name='" + name + '\'' + '}'; } } NbaPlayer[] players = Arrays.stream(names).map(NbaPlayer::new).toArray(NbaPlayer[]::new); Arrays.stream(players).forEach(System.out::println);
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That's all for now. Maybe in the next post I'll do more with streams and other data structures. ArrayLists for sure. 👨🏽‍💻

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