Why does resizing takes place if all the elements are ended in same bucked?

I have written below code to test the behavior of hashmap when all elements are ended in the same bucket:-

public class DerivedMain {

int data = 10;

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

public static void main(String[] args) {

    HashMap m = new HashMap();
    for(int i=0;i<20;i++) {
        m.put(i, i);
    }

    Field tableField = null;
    try {
        tableField = HashMap.class.getDeclaredField("table");
    } catch (NoSuchFieldException | SecurityException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    tableField.setAccessible(true);
    Object[] table = null;
    try {
        table = (Object[]) tableField.get(m);
    } catch (IllegalArgumentException | IllegalAccessException e) 
            {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    System.out.println(table == null ? 0 : table.length);
}

}

I got the following output:- 32

Why is resizing happening even when all the elements are ending in same bucket?