MapTest.java

import java.lang.reflect.Field;
import java.util.HashMap;

public class MapTest {
    private static class X {
        private int value;

        public X(int value) {
            this.value = value;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }
            X x = (X) o;
            return value == x.value;
        }

        @Override
        public int hashCode() {
            return 1;
        }
    }

    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < 16; i++) {
            printMap(map);
            map.put(i, i);
        }

        System.out.println();

        HashMap<X, Integer> map2 = new HashMap<>();
        for (int i = 0; i < 16; i++) {
            printMap(map2);
            map2.put(new X(i), i);
        }
    }

    private static void printMap(HashMap<?, ?> map) throws NoSuchFieldException, IllegalAccessException {
        System.out.println("map.size() = " + map.size());
        Field internalTable = HashMap.class.getDeclaredField("table");
        internalTable.setAccessible(true);
        Object[] table = (Object[]) internalTable.get(map);
        if (table == null) {
            System.out.println("table = " + null);
        }
        else {
            System.out.println("table.length = " + table.length);
        }
    }
}