DragImageExchange.java

package net.squiz.matrix.ui;

import java.awt.image.BufferedImage;
import java.awt.Point;

public class DragImageExchange {

    private static BufferedImage dragImage;
    private static Point mouseOffset;
    private static boolean inExchange = false;

    // cannot instantiate
    private DragImageExchange() {}

    public static void setDragImage(BufferedImage dragImage, Point mouseOffset) {
        //if (inExchange)
        //  throw new IllegalStateException("There is already an exchange open.");
        DragImageExchange.dragImage = dragImage;
        DragImageExchange.mouseOffset = mouseOffset;
        inExchange = true;
    }

    public static BufferedImage getDragImage() {
        if (!inExchange)
            throw new IllegalStateException("There is no exchange open.");
        return dragImage;
    }

    public static Point getMouseOffset() {
        if (!inExchange)
            throw new IllegalStateException("There is no exchange open.");
        return mouseOffset;
    }

    public static void completeExchange() {
        if (!inExchange)
            throw new IllegalStateException("There is no exchange open.");
        dragImage = null;
        inExchange = false;
    }
}