The code below demonstrates a number of problems with the modifiers field of manually constructed MouseEvents.

import java.awt.*;
import java.awt.event.*;

public class MouseEventConstruction {
    final static int inmods[] = {
        InputEvent.BUTTON1_MASK,
        InputEvent.BUTTON1_MASK | InputEvent.ALT_MASK,
        InputEvent.BUTTON1_MASK | InputEvent.SHIFT_MASK,
        InputEvent.BUTTON1_MASK | InputEvent.META_MASK,
        InputEvent.BUTTON1_MASK | InputEvent.CTRL_MASK,
        InputEvent.BUTTON1_MASK | InputEvent.SHIFT_MASK | InputEvent.ALT_MASK,
        InputEvent.BUTTON1_MASK | InputEvent.BUTTON2_MASK,
        InputEvent.BUTTON2_MASK | InputEvent.ALT_MASK,
        InputEvent.BUTTON2_MASK | InputEvent.SHIFT_MASK,
        InputEvent.BUTTON2_MASK | InputEvent.META_MASK,
        InputEvent.BUTTON2_MASK | InputEvent.CTRL_MASK,
        };
    final static int numEvents = inmods.length;

    public static void main(String[] args) {
        Frame dummy = new Frame("dummy");
        MouseEvent event;
        for(int loop = 0; loop < numEvents; loop++) {
            event = new MouseEvent(dummy,
                                   MouseEvent.MOUSE_PRESSED,
                                   0,
                                   inmods[loop],
                                   0,0,0,false);
            if (event.getModifiers() != inmods[loop]) {
                System.out.println("[" + loop + "]Test failed for mask " + inmods[loop] + ", got: " + event.getModifiers());
            }
        }
        System.out.println("Test done.");
    }
}