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Java Holiday Calendar 2016 (Day 3): Initializing Maps in the Smartest Way

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Java Holiday Calendar 2016 (Day 3): Initializing Maps in the Smartest Way

Learn how you can create and initialize type-safe maps in Java by using two simple utility methods.

· Java Zone ·
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Today's tip is how to initialize Java Maps in a type-safe way with Java 8. With Java 9, we will get even better ways of creating immutable Maps. Until then, by defining two utility methods...

    public static <K, V> Entry<K, V> entry(K key, V value) {
        return new AbstractMap.SimpleEntry<>(key, value);
    }
    public static <K, U> Collector<Entry<K, U>, ?, Map<K, U>> entriesToMap() {
        return Collectors.toMap(Entry::getKey, Entry::getValue);
    }


...you can do this:

protected static Map<Integer, String> createMap() {
        return Stream.of(
                entry(0, "zero"),
                entry(1, "one"),
                entry(2, "two"),
                entry(3, "three"),
                entry(4, "four"),
                entry(5, "five"),
                entry(6, "six"),
                entry(7, "seven"),
                entry(8, "eight"),
                entry(9, "nine"),
                entry(10, "ten"),
                entry(11, "eleven"),
                entry(12, "twelve")).
                collect(entriesToMap());
    }


You can read more about initializing maps here.

Follow the Java Holiday Calendar 2016 with small tips and tricks all the way through the winter holiday season.

Learn how to build distributed stream processing applications in Java that elastically scale to meet demand- includes reference application.  Brought to you in partnership with Hazelcast.

Topics:
java ,maps ,immutable ,type-safe

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