Discussion
What will be the output of the program?
import java.util.*;
public class Fragment06
{
public static void main(String[] args)
{
Map<String, String> m = new HashMap<String, String>();
m.put(null, "one");
m.put(null, "two");
System.out.println(m.get(null) + " " + m.size());
}
}
Answer: B
HashMap permits one null key, so this stores an entry and then overwrites its value, leaving the map with a single entry holding two. Hashtable and TreeMap both reject a null key with a NullPointerException, which is the distinction being tested.
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