You can apply a custom formatter to make the labels print whatever you want. In your case, I believe something like this should work:
plot.setDomainValueFormat(new NumberFormat() {
@Override
public StringBuffer format(double d, StringBuffer sb, FieldPosition fp) {
return sb.append((d + 1) + ""); // shortcut to convert d+1 into a String
}
// unused
@Override
public StringBuffer format(long l, StringBuffer stringBuffer, FieldPosition fieldPosition) { return null;}
// unused
@Override
public Number parse(String s, ParsePosition parsePosition) { return null;}
});