Add CloseConfirmable interface

This interface is intended for UI components that get user input to deal
with unsaved state before closing.

With this we create an opt-in clean-up mechanism for close operations.

Author: hinerm

src/main/java/org/scijava/ui/CloseConfirmable.java

@@ -0,0 +1,54 @@
+/*
+ * #%L
+ * SciJava Common shared library for SciJava software.
+ * %%
+ * Copyright (C) 2009 - 2014 Board of Regents of the University of
+ * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
+ * Institute of Molecular Cell Biology and Genetics.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.ui;
+
+/**
+ * Interface for UI components that require the user to deal with changed state
+ * before the component can be closed. The {@link #confirmClose()} method should
+ * <p>
+ * For example, a text editor that monitors unsaved changes would implement this
+ * interface. Its {@code confirmClose} method would, if unsaved changes exist,
+ * ask the user if they would like to save said changes, e.g. with a
+ * {@code Yes-No-Cancel} dialog. The method would return {@code true} if
+ * {@code Yes} or {@code No} was selected in this case, and {@code false} if
+ * {@code Cancel}ed.
+ * </p>
+ *
+ * @author Mark Hiner
+ */
+public interface CloseConfirmable {
+
+	/**
+	 * @return {@code true} if the current close operation should continue.
+	 */
+	boolean confirmClose();
+}