Index: trunk/src/org/openstreetmap/josm/gui/MainApplication.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/MainApplication.java	(revision 12669)
+++ trunk/src/org/openstreetmap/josm/gui/MainApplication.java	(revision 12670)
@@ -210,9 +210,51 @@
     }
 
+    /**
+     * Asks user to update its version of Java.
+     * @param updVersion target update version
+     * @param url download URL
+     * @param major true for a migration towards a major version of Java (8:9), false otherwise
+     * @param eolDate the EOL/expiration date
+     * @since 12270
+     */
+    public static void askUpdateJava(String updVersion, String url, String eolDate, boolean major) {
+        ExtendedDialog ed = new ExtendedDialog(
+                Main.parent,
+                tr("Outdated Java version"),
+                tr("OK"), tr("Update Java"), tr("Cancel"));
+        // Check if the dialog has not already been permanently hidden by user
+        if (!ed.toggleEnable("askUpdateJava"+updVersion).toggleCheckState()) {
+            ed.setButtonIcons("ok", "java", "cancel").setCancelButton(3);
+            ed.setMinimumSize(new Dimension(480, 300));
+            ed.setIcon(JOptionPane.WARNING_MESSAGE);
+            StringBuilder content = new StringBuilder(tr("You are running version {0} of Java.",
+                    "<b>"+System.getProperty("java.version")+"</b>")).append("<br><br>");
+            if ("Sun Microsystems Inc.".equals(System.getProperty("java.vendor")) && !platform.isOpenJDK()) {
+                content.append("<b>").append(tr("This version is no longer supported by {0} since {1} and is not recommended for use.",
+                        "Oracle", eolDate)).append("</b><br><br>");
+            }
+            content.append("<b>")
+                   .append(major ?
+                        tr("JOSM will soon stop working with this version; we highly recommend you to update to Java {0}.", updVersion) :
+                        tr("You may face critical Java bugs; we highly recommend you to update to Java {0}.", updVersion))
+                   .append("</b><br><br>")
+                   .append(tr("Would you like to update now ?"));
+            ed.setContent(content.toString());
+
+            if (ed.showDialog().getValue() == 2) {
+                try {
+                    platform.openUrl(url);
+                } catch (IOException e) {
+                    Logging.warn(e);
+                }
+            }
+        }
+    }
+
     @Override
     protected List<InitializationTask> beforeInitializationTasks() {
         return Arrays.asList(
             new InitializationTask(tr("Starting file watcher"), fileWatcher::start),
-            new InitializationTask(tr("Executing platform startup hook"), platform::startupHook),
+            new InitializationTask(tr("Executing platform startup hook"), () -> platform.startupHook(MainApplication::askUpdateJava)),
             new InitializationTask(tr("Building main menu"), this::initializeMainWindow),
             new InitializationTask(tr("Updating user interface"), () -> {
Index: trunk/src/org/openstreetmap/josm/tools/PlatformHook.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/PlatformHook.java	(revision 12669)
+++ trunk/src/org/openstreetmap/josm/tools/PlatformHook.java	(revision 12670)
@@ -2,7 +2,4 @@
 package org.openstreetmap.josm.tools;
 
-import static org.openstreetmap.josm.tools.I18n.tr;
-
-import java.awt.Dimension;
 import java.awt.GraphicsEnvironment;
 import java.io.BufferedReader;
@@ -20,8 +17,5 @@
 import java.util.List;
 
-import javax.swing.JOptionPane;
-
 import org.openstreetmap.josm.Main;
-import org.openstreetmap.josm.gui.ExtendedDialog;
 import org.openstreetmap.josm.io.CertificateAmendment.CertAmend;
 import org.openstreetmap.josm.tools.date.DateUtils;
@@ -61,6 +55,8 @@
       * Reason: On OSX we need to register some callbacks with the
       * OS, so we'll receive events from the system menu.
-      */
-    default void startupHook() {
+     * @param callback Java expiration callback, providing GUI feedback
+     * @since 12270 (signature)
+      */
+    default void startupHook(JavaExpirationCallback callback) {
         // Do nothing
     }
@@ -246,54 +242,30 @@
 
     /**
-     * Asks user to update its version of Java.
-     * @param updVersion target update version
-     * @param url download URL
-     * @param major true for a migration towards a major version of Java (8:9), false otherwise
-     * @param eolDate the EOL/expiration date
+     * Called when an outdated version of Java is detected at startup.
+     * @since 12270
+     */
+    @FunctionalInterface
+    public interface JavaExpirationCallback {
+        /**
+         * Asks user to update its version of Java.
+         * @param updVersion target update version
+         * @param url download URL
+         * @param major true for a migration towards a major version of Java (8:9), false otherwise
+         * @param eolDate the EOL/expiration date
+         */
+        void askUpdateJava(String updVersion, String url, String eolDate, boolean major);
+    }
+
+    /**
+     * Checks if the running version of Java has expired, proposes to user to update it if needed.
+     * @param callback Java expiration callback
+     * @since 12270 (signature)
      * @since 12219
      */
-    default void askUpdateJava(String updVersion, String url, String eolDate, boolean major) {
-        ExtendedDialog ed = new ExtendedDialog(
-                Main.parent,
-                tr("Outdated Java version"),
-                tr("OK"), tr("Update Java"), tr("Cancel"));
-        // Check if the dialog has not already been permanently hidden by user
-        if (!ed.toggleEnable("askUpdateJava"+updVersion).toggleCheckState()) {
-            ed.setButtonIcons("ok", "java", "cancel").setCancelButton(3);
-            ed.setMinimumSize(new Dimension(480, 300));
-            ed.setIcon(JOptionPane.WARNING_MESSAGE);
-            StringBuilder content = new StringBuilder(tr("You are running version {0} of Java.",
-                    "<b>"+System.getProperty("java.version")+"</b>")).append("<br><br>");
-            if ("Sun Microsystems Inc.".equals(System.getProperty("java.vendor")) && !isOpenJDK()) {
-                content.append("<b>").append(tr("This version is no longer supported by {0} since {1} and is not recommended for use.",
-                        "Oracle", eolDate)).append("</b><br><br>");
-            }
-            content.append("<b>")
-                   .append(major ?
-                        tr("JOSM will soon stop working with this version; we highly recommend you to update to Java {0}.", updVersion) :
-                        tr("You may face critical Java bugs; we highly recommend you to update to Java {0}.", updVersion))
-                   .append("</b><br><br>")
-                   .append(tr("Would you like to update now ?"));
-            ed.setContent(content.toString());
-
-            if (ed.showDialog().getValue() == 2) {
-                try {
-                    openUrl(url);
-                } catch (IOException e) {
-                    Logging.warn(e);
-                }
-            }
-        }
-    }
-
-    /**
-     * Checks if the running version of Java has expired, proposes to user to update it if needed.
-     * @since 12219
-     */
-    default void checkExpiredJava() {
+    default void checkExpiredJava(JavaExpirationCallback callback) {
         Date expiration = Utils.getJavaExpirationDate();
         if (expiration != null && expiration.before(new Date())) {
             String version = Utils.getJavaLatestVersion();
-            askUpdateJava(version != null ? version : "latest",
+            callback.askUpdateJava(version != null ? version : "latest",
                     Main.pref.get("java.update.url", "https://www.java.com/download"),
                     DateUtils.getDateFormat(DateFormat.MEDIUM).format(expiration), false);
Index: trunk/src/org/openstreetmap/josm/tools/PlatformHookOsx.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/PlatformHookOsx.java	(revision 12669)
+++ trunk/src/org/openstreetmap/josm/tools/PlatformHookOsx.java	(revision 12670)
@@ -48,5 +48,5 @@
 
     @Override
-    public void startupHook() {
+    public void startupHook(JavaExpirationCallback callback) {
         // Here we register callbacks for the menu entries in the system menu and file opening through double-click
         // http://openjdk.java.net/jeps/272
@@ -79,5 +79,5 @@
             Logging.warn("Failed to register with OSX: " + ex);
         }
-        checkExpiredJava();
+        checkExpiredJava(callback);
     }
 
Index: trunk/src/org/openstreetmap/josm/tools/PlatformHookWindows.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/PlatformHookWindows.java	(revision 12669)
+++ trunk/src/org/openstreetmap/josm/tools/PlatformHookWindows.java	(revision 12670)
@@ -183,6 +183,6 @@
 
     @Override
-    public void startupHook() {
-        checkExpiredJava();
+    public void startupHook(JavaExpirationCallback callback) {
+        checkExpiredJava(callback);
     }