Hashtable and nulls

Если коротко, то Hashtable не поддерживает null'ы ни в каком виде:

	import java.util.Hashtable;
	import java.util.Properties;
	public class HashtableTest {
	public static void main(String[] args) {
	Properties p = new Properties();
	if (p instanceof Hashtable) {
	System.out.println("java.util.Properties is a subclass of java.util.Hashtable");
	}
	try {
	p.put(null, "value");
	} catch (NullPointerException npe) {
	System.out.println("Hashtable does NOT support addition of null KEYs!");
	}
	try {
	p.put("key", null);
	} catch (NullPointerException npe) {
	System.out.println("Hashtable does NOT support addition of null VALUEs!");
	}
	try {
	if (!p.contains(null)) {
	System.out.println("Does not contain null.");
	}
	} catch (NullPointerException npe) {
	System.out.println("Hashtable does NOT support check for null keys!");
	}
	}
	}
	/* OUTPUT:
	java.util.Properties is a subclass of java.util.Hashtable
	Hashtable does NOT support addition of null KEYs!
	Hashtable does NOT support addition of null VALUEs!
	Hashtable does NOT support check for null keys!
	*/

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