DragExchange.java

package net.squiz.matrix.ui;

import java.awt.datatransfer.*;
import net.squiz.matrix.matrixtree.MatrixTreeTransferable;
import java.awt.*;
import java.util.*;
import javax.swing.tree.*;

public class DragExchange {

    private static MatrixTreeTransferable transfer;
    private static Draggable dragSource;
    private static boolean inExchange = false;
    // cannot instantiate
    private DragExchange() {}

    public static void setTransferable(Draggable dragSource, MatrixTreeTransferable transfer) {
        if (inExchange)
            throw new IllegalStateException("There is already an exchange open by " + dragSource.getClass());
        DragExchange.transfer = transfer;
        DragExchange.dragSource = dragSource;
        inExchange = true;
    }

    public static MatrixTreeTransferable getTransferable() {
        if (!inExchange)
            throw new IllegalStateException("There is no exchange open");
        return transfer;
    }

    public static Draggable getSource() {
        if (!inExchange)
            throw new IllegalStateException("There is no exchange open");
        return dragSource;
    }

    public static TreePath[] getDragPaths() {
        if (!inExchange)
            throw new IllegalStateException("There is no exchange open");
        java.util.List paths = null;
        try {
            paths = (java.util.List) transfer.getTransferData(
                MatrixTreeTransferable.TREE_NODE_FLAVOUR);
        } catch (UnsupportedFlavorException ufe) {
        //  GUIUtilties.error();
            ufe.printStackTrace();
        } catch (java.io.IOException ioe) {
        //  GUIUtilties.error();
            ioe.printStackTrace();
        }
        return (TreePath[]) paths.toArray(new TreePath[paths.size()]);
    }

    public static Image translateImage(Draggable draggable) {
        if (!inExchange)
            throw new IllegalStateException("There is no exchange open");
        TreePath[] pathsArr = getDragPaths();

        return draggable.getDragImage(pathsArr);
    }

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