We need more context. In regular Processing, there is not PApplet.main() line, for example.

    // Your Serial Port
    Serial port;
    // Your XBee Reader object
    XBeeReader xbee;

    int ad64H=0x0013A200;
    int [] ad64L={0x403E17E5,0x403E17E6,0x403E17E3};
    int [] ad16={0xFFFE,0xFFFE,0xFFFE};
    String [] ni={" 204"," 203"," 205"};

   
    static public void main(String args[]) {
        PApplet.main(new String[] { "processing.XBee"});
    }

Again, lack of context. This code is to be run in an IDE like Eclipse, not in the PDE.

If you want to run it in the latter, remove:
import processing.core.*;
import processing.serial.*;
and
    static public void main(String args[]) {
        PApplet.main(new String[] { "processing.XBee"});
    }

Mmm, it isn't valid IDE code either, missing a class around your methods and field declarations...