Basic HTML version of Foils prepared 18 May 97

Foil 23 The Hashtable class

From Java Tutorial - Spring 1997 Part 4: Multithreading, useful Java classes, I/O, Networking, and the future Peking Tutorial, Web Certificate -- Spring-Summer 1997. by Nancy J. McCracken,Geoffrey C. Fox


This class is similar to the Perl associative array (or hash array with {} brackets). It can store a set of key and value pairs, neither of which can be null.
  • Hashtable staff = new Hashtable();
  • Employee harry = new Employee("Harry Hacker");
  • staff.put("987-98-9996", harry);
Values are retrieved by indexing with a key. Like Vectors, Hashtables only store things of type Object and you must cast the result.
  • steve = (Employee) staff.get("149-26-7355");
If there was no entry, a null is returned.
Performance of the Hashtable can also be affected by giving an initialCapacity and a loadFactor for reallocation.



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