Can java.util.HashMap store null key/value pair?
Yes it can, However only one null key is allowed, but can store many null values against non-null keys
Example
public class HashMapTest
{
public static void main(String args[])
{
HashMap h = new HashMap();
h.put(null,null);
h.put(null, "1");
h.put("1", null);
h.put("1", "1");
h.put("2", null);
System.out.println(h.get(null).toString());
System.out.println(h.get("1"));
System.out.println(h.get("2"));
}
}
output
1
1
null
Can java.util.Hashtable store null key/value pair?
No it can’t. We cannot store null keys or null values or both in the Hashtable, java.lang.NullPointerException will be thrown.
import java.util.Hashtable;
public class HashTableTest
{
public static void main(String args[])
{
Hashtable h = new Hashtable();
//h.put(null,null); //NullPointerException
//h.put(null, "1"); //NullPointerException
//h.put("1", null); //NullPointerException
h.put("1", "1");
//h.put("2", null); //NullPointerException
//System.out.println(h.get(null).toString()); //NullPointerException
System.out.println(h.get("1")); //1
System.out.println(h.get("2")); //null
}
}
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