You want to use HashMap. There are no hash literals as there are in scripting languages like Perl, Python, or Ruby; you have to use explicit method calls. In Java 5:
import java.util.*;
...
Map<
String, String> myHash = new HashMap<String, String>();
myHash.put("A", "a");
myHash.put("B", "b");
myHash.put("C", "c");
String myLowerCaseLetter = myHash.get(myUpperCaseLetter);
[ EJFH: Added Garrett's corrections ]
[ July 13, 2006: Message edited by: Ernest Friedman-Hill ]