One trick to teach you how to quickly create a Map using Java (code sharing)-javaTutorial-php.cn

One trick to teach you how to quickly create a Map using Java (code sharing)

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Release： 2021-09-14 13:19:15

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In the previous article "Understanding the new java.util.function.*pojo reflection method in java8 (with code)", we learned about the new pojo reflection method in java8. The following article will introduce to you how to use java to quickly create a Map. Let's see how to do it together.

One trick to teach you how to quickly create a Map using Java (code sharing)

If you want to quickly create a Map without frequent new, the fastest way is to use Guava , use ImmutableMap.of("a", 1, "b", 2, "c", 3);

Guava

Map<String, Integer> left = ImmutableMap.of("a", 1, "b", 2, "c", 3);

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java9

Map<Integer, String> map = Map.of(1, "A", 2, "B", 3, "C");

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More than 10 groups will not be supported, so it will be like this:

Map.ofEntries(
    Map.entry( 1, false ),
    Map.entry( 2, true ),
    Map.entry( 3, false ),
    Map.entry( 4, true ),
    Map.entry( 5, false ),
    Map.entry( 6, true ),
    Map.entry( 7, false ),
    Map.entry( 8, true ),
    Map.entry( 9, false ),
    Map.entry( 10, true ),
    Map.entry( 11, false )
);

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Anonymous

Map<Integer, String> mymap = new HashMap<Integer, String>() {
	{
		put(1, "one");
		put(2, "two");
	}
};
Collections.unmodifiableMap(new HashMap<Integer, String>() {
            {
                put(0, "zero");
                put(1, "one");
                put(2, "two");
                put(3, "three");
                put(4, "four");
                put(5, "five");
                put(6, "six");
                put(7, "seven");
                put(8, "eight");
                put(9, "nine");
                put(10, "ten");
                put(11, "eleven");
                put(12, "twelve");
            }
        });

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