Hmm, just to add to this, you can overload methods with different
argument types and have them on the same class.

public String receivedData(String s)

public byte[] receivedData(byte[] b)

That won't help out the OP, just thought I'd throw that out. ;)

The best way is probably to refactor/redesign what he/she has.  There
are many patterns that may help.

Besides rewriting the program in Ada?

They could use a "return variable in the input" idiom and make
do something like the following:

public void receivedData( String[] returnValue ) {
  ...
 returnValue[0] = someString;
}

public void receivedData( byte[][] returnValue ) {
 ...
 returnValue[0] = someByteArray;
}

public doMagic( ) {

 String[] stringWrapper = new String[1];
 receivedData( stringWrapper );
 doStringStuff( stringWrapper[0] );

 byte[][] byteWrapper = new byte[][1];
 receivedData( byteWrapper );
 doByteStuff( byteWrapper[0] );

}

It's rather cumbersome, though. A cleaner way would be to use "marker
parameters":

public String receivedData( String dummy ) {
 return someString;
}

public byte[] receivedData( byte[] dummy ) {
 return someByteArray;
}

public doMagic( ) {
 String receivedString = receivedData( "String" );
 byte[] receivedByteArray = receivedData( new byte[0] );
}

It's not a very "javaesque" way to do things, though. It's a pretty weird
thing to do in a java program, and is likely to confuse a whole lot more
than it helps, so I wouldn't recommend it.