Answer 1

A hashtable is used to map keys to values.
for example:

Hashtable<String, Integer> table =
new Hashtable<String, Integer>();
table.put("key1", 2);
table.put("key2", 7);
table.put("key3", 18);

You can read the values with the get() of your Hashtable method:

System.out.print(table.get("key2")); // 7