Java does not directly support EBCDIC. There are actually a large number of EBCDIC variations. Java does support a number of encodings related to EBCDIC. For example, the 'Cp1047' encoding is defined as "Latin-1 character set for EBCDIC hosts".
[EBCDIC is] not directly supported. EBCDIC comes in dozens of variants, most of which do not have Java support. Check out Cp037, Cp038, Cp278, Cp280, Cp284, Cp285, Cp297, Cp424, Cp500, Cp871, Cp918, Cp1046, Cp1047, Cp1048, Cp1148.
Also, to the best of my knowledge, you cannot change the encoding of a String. Since you used "String" with an uppercase 'S' I am assuming you are referring to the String class. Java stores all strings internally via unicode or UTF-16.
You can encode a string (lowercase 's') when you write it to a stream (to a file, the console, a network connection, etc). Some of the various stream classes and reader & writer classes support taking an encoding definition.