CellDemo.java shows how. See https://code.google.com/p/gdata-java-client/source/browse/trunk/java/sample/spreadsheet/cell/CellDemo.java?r=51
From CellDemo.java:
/**
* Prints out the specified cell.
*
* @param cell the cell to print
*/
public void printCell(CellEntry cell) {
String shortId = cell.getId().substring(cell.getId().lastIndexOf('/') + 1);
out.println(" -- Cell(" + shortId + "/" + cell.getTitle().getPlainText()
+ ") formula(" + cell.getCell().getInputValue() + ") numeric("
+ cell.getCell().getNumericValue() + ") value("
+ cell.getCell().getValue() + ")");
}