OptimalMapSize.java

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/**
 * @test
 * @bug 8080535 8191410 8215194 8221431 8239383
 * @summary Expected size of Character.UnicodeBlock.map is not optimal
 * @library /test/lib
 * @modules java.base/java.lang:open
 *          java.base/java.util:open
 * @build jdk.test.lib.util.OptimalCapacity
 * @run main OptimalMapSize
 */

import java.lang.reflect.Field;
import jdk.test.lib.util.OptimalCapacity;

// What will be the number of the Unicode blocks in the future.
//
// According to http://www.unicode.org/versions/Unicode7.0.0/ ,
// in Unicode 7 there will be added 32 new blocks (96 with aliases).
// According to http://www.unicode.org/versions/beta-8.0.0.html ,
// in Unicode 8 there will be added 10 more blocks (30 with aliases).
//
// After implementing support of Unicode 9 and 10 in Java, there will
// be 638 entries in Character.UnicodeBlock.map.
//
// As of Unicode 11, 667 entries are expected.
// As of Unicode 12.1, 676 entries are expected.
// As of Unicode 13.0, 684 entries are expected.
//
// Initialization of the map and this test will have to be adjusted
// accordingly then.
//
// Note that HashMap's implementation aligns the initial capacity to
// a power of two size, so it will end up 1024 (and thus succeed) in
// cases, such as 638, 667, 676, and 684.

public class OptimalMapSize {
    public static void main(String[] args) throws Throwable {
        // The initial size of Character.UnicodeBlock.map.
        // See src/java.base/share/classes/java/lang/Character.java
        Field f = Character.UnicodeBlock.class.getDeclaredField("NUM_ENTITIES");
        f.setAccessible(true);
        int num_entities = f.getInt(null);
        assert num_entities == 684;
        int initialCapacity = (int)(num_entities / 0.75f + 1.0f);

        OptimalCapacity.ofHashMap(Character.UnicodeBlock.class,
                "map", initialCapacity);
    }
}