How to determine the number of buckets in a HashMap data structure?

In Java, the HashMap data structure uses a bucket array to store key-value pairs. The number of buckets corresponds to the internal capacity of the HashMap and affects performance.

The number of buckets can be determined using the capacity() method, but it is not public. However, you can indirectly obtain the current number of buckets:

• Use reflection to access the private table field (the array of buckets) and find its length.
• Or use the size() method for the number of elements, but this is not the number of buckets.

Example with reflection:

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

HashMap<String, String> map = new HashMap<>();
map.put("key", "value");

Field tableField = HashMap.class.getDeclaredField("table");
tableField.setAccessible(true);
Object[] table = (Object[]) tableField.get(map);
int bucketCount = table == null ? 0 : table.length;
System.out.println("Number of buckets: " + bucketCount);

Note that the internal implementation of HashMap may change between Java versions, so this approach is not always reliable.