How can I initialise a static Map?

Question

How would you initialise a static Map in Java?

Method one: static initialiser
Method two: instance initialiser (anonymous subclass) or some other m

Answer 1

Java 9

We can use Map.ofEntries, calling Map.entry( k , v ) to create each entry.

import static java.util.Map.entry;
private static final Map map = Map.ofEntries(
        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"));

We can also use Map.of as suggested by Tagir in his answer here but we cannot have more than 10 entries using Map.of.

Java 8 (Neat Solution)

We can create a Stream of map entries. We already have two implementations of Entry in java.util.AbstractMap which are SimpleEntry and SimpleImmutableEntry. For this example we can make use of former as:

import java.util.AbstractMap.*;
private static final Map myMap = Stream.of(
            new SimpleEntry<>(1, "one"),
            new SimpleEntry<>(2, "two"),
            new SimpleEntry<>(3, "three"),
            new SimpleEntry<>(4, "four"),
            new SimpleEntry<>(5, "five"),
            new SimpleEntry<>(6, "six"),
            new SimpleEntry<>(7, "seven"),
            new SimpleEntry<>(8, "eight"),
            new SimpleEntry<>(9, "nine"),
            new SimpleEntry<>(10, "ten"))
            .collect(Collectors.toMap(SimpleEntry::getKey, SimpleEntry::getValue));