Improve type safety of the fluent interface of Overlay<T>

Refactor all the unchecked casts from Overlay<T> to T into a single
private cast() method. Also add a runtime type check to the constructor
to prevent creation of window objects of the form "A extends Overlay<B>"
for unrelated A & B, as such casts would then subvert the type system.

desktop/src/main/java/bisq/desktop/main/overlays/Overlay.java

@@ -29,14 +29,16 @@ import bisq.desktop.util.Transitions;
 
 import bisq.core.app.BisqEnvironment;
 import bisq.core.locale.GlobalSettings;
+import bisq.core.locale.LanguageUtil;
 import bisq.core.locale.Res;
 import bisq.core.user.DontShowAgainLookup;
-import bisq.core.locale.LanguageUtil;
 
 import bisq.common.Timer;
 import bisq.common.UserThread;
 import bisq.common.util.Utilities;
 
+import com.google.common.reflect.TypeToken;
+
 import org.apache.commons.lang3.StringUtils;
 
 import de.jensd.fx.fontawesome.AwesomeIcon;
@@ -68,8 +70,8 @@ import javafx.scene.transform.Rotate;
 
 import javafx.geometry.HPos;
 import javafx.geometry.Insets;
-import javafx.geometry.Pos;
 import javafx.geometry.NodeOrientation;
+import javafx.geometry.Pos;
 
 import javafx.beans.property.BooleanProperty;
 import javafx.beans.property.SimpleBooleanProperty;
@@ -93,7 +95,7 @@ import lombok.Setter;
 import lombok.extern.slf4j.Slf4j;
 
 @Slf4j
-public abstract class Overlay<T extends Overlay> {
+public abstract class Overlay<T extends Overlay<T>> {
 
     ///////////////////////////////////////////////////////////////////////////////////////////
     // Enum
@@ -185,12 +187,23 @@ public abstract class Overlay<T extends Overlay> {
 
     protected int maxChar = 1800;
 
+    private T cast() {
+        //noinspection unchecked
+        return (T) this;
+    }
+
 
     ///////////////////////////////////////////////////////////////////////////////////////////
     // Public API
     ///////////////////////////////////////////////////////////////////////////////////////////
 
     public Overlay() {
+        //noinspection UnstableApiUsage
+        TypeToken<T> typeToken = new TypeToken<>(getClass()) {
+        };
+        if (!typeToken.isSupertypeOf(getClass())) {
+            throw new RuntimeException("Subclass of Overlay<T> should be castable to T");
+        }
     }
 
     public void show(boolean showAgainChecked) {
@@ -266,26 +279,22 @@ public abstract class Overlay<T extends Overlay> {
 
     public T onClose(Runnable closeHandler) {
         this.closeHandlerOptional = Optional.of(closeHandler);
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T onAction(Runnable actionHandler) {
         this.actionHandlerOptional = Optional.of(actionHandler);
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T onSecondaryAction(Runnable secondaryActionHandlerOptional) {
         this.secondaryActionHandlerOptional = Optional.of(secondaryActionHandlerOptional);
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T headLine(String headLine) {
         this.headLine = headLine;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T notification(String message) {
@@ -294,8 +303,7 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.notification");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T instruction(String message) {
@@ -304,8 +312,7 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.instruction");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T attention(String message) {
@@ -314,8 +321,7 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.attention");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T backgroundInfo(String message) {
@@ -324,8 +330,7 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.backgroundInfo");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T feedback(String message) {
@@ -334,8 +339,7 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.feedback");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T confirmation(String message) {
@@ -344,8 +348,7 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.confirmation");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T information(String message) {
@@ -354,8 +357,7 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.information");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T warning(String message) {
@@ -365,8 +367,7 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.warning");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T error(String message) {
@@ -377,136 +378,116 @@ public abstract class Overlay<T extends Overlay> {
             this.headLine = Res.get("popup.headline.error");
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     @SuppressWarnings("UnusedReturnValue")
     public T showReportErrorButtons() {
         this.showReportErrorButtons = true;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T message(String message) {
         this.message = message;
         setTruncatedMessage();
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T closeButtonText(String closeButtonText) {
         this.closeButtonText = closeButtonText;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T useReportBugButton() {
         this.closeButtonText = Res.get("shared.reportBug");
         this.closeHandlerOptional = Optional.of(() -> GUIUtil.openWebPage("https://bisq.network/source/bisq/issues"));
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T useIUnderstandButton() {
         this.closeButtonText = Res.get("shared.iUnderstand");
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T actionButtonTextWithGoTo(String target) {
         this.actionButtonText = Res.get("shared.goTo", Res.get(target));
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T secondaryActionButtonTextWithGoTo(String target) {
         this.secondaryActionButtonText = Res.get("shared.goTo", Res.get(target));
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T closeButtonTextWithGoTo(String target) {
         this.closeButtonText = Res.get("shared.goTo", Res.get(target));
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T actionButtonText(String actionButtonText) {
         this.actionButtonText = actionButtonText;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T secondaryActionButtonText(String secondaryActionButtonText) {
         this.secondaryActionButtonText = secondaryActionButtonText;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T useShutDownButton() {
         this.actionButtonText = Res.get("shared.shutDown");
         this.actionHandlerOptional = Optional.ofNullable(BisqApp.getShutDownHandler());
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T buttonAlignment(HPos pos) {
         this.buttonAlignment = pos;
-        return (T) this;
+        return cast();
     }
 
     public T width(double width) {
         this.width = width;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T maxMessageLength(int maxChar) {
         this.maxChar = maxChar;
-        return (T) this;
+        return cast();
     }
 
     public T showBusyAnimation() {
         this.showBusyAnimation = true;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T dontShowAgainId(String key) {
         this.dontShowAgainId = key;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T dontShowAgainText(String dontShowAgainText) {
         this.dontShowAgainText = dontShowAgainText;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T hideCloseButton() {
         this.hideCloseButton = true;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T useAnimation(boolean useAnimation) {
         this.useAnimation = useAnimation;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T setHeadlineStyle(String headlineStyle) {
         this.headlineStyle = headlineStyle;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
     public T disableActionButton() {
         this.disableActionButton = true;
-        //noinspection unchecked
-        return (T) this;
+        return cast();
     }
 
 

desktop/src/main/java/bisq/desktop/main/overlays/TabbedOverlay.java

@@ -4,7 +4,7 @@ import com.jfoenix.controls.JFXTabPane;
 
 import javafx.scene.layout.Region;
 
-public abstract class TabbedOverlay<T extends TabbedOverlay> extends Overlay {
+public abstract class TabbedOverlay<T extends TabbedOverlay<T>> extends Overlay<T> {
 
     protected JFXTabPane tabPane;
 

desktop/src/main/java/bisq/desktop/main/overlays/popups/Popup.java

@@ -22,7 +22,8 @@ import bisq.desktop.main.overlays.Overlay;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-public class Popup<T extends Overlay> extends Overlay<Popup> {
+// TODO: Type parameter is unused - remove:
+public class Popup<T> extends Overlay<Popup<T>> {
     protected final Logger log = LoggerFactory.getLogger(this.getClass());
 
     public Popup() {
@@ -41,6 +42,4 @@ public class Popup<T extends Overlay> extends Overlay<Popup> {
     protected void onHidden() {
         PopupManager.onHidden(this);
     }
-
-
 }

desktop/src/test/java/bisq/desktop/main/overlays/OverlayTest.java

@@ -0,0 +1,47 @@
+/*
+ * This file is part of Bisq.
+ *
+ * Bisq is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Bisq is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Bisq. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package bisq.desktop.main.overlays;
+
+import org.junit.Test;
+
+public class OverlayTest {
+
+    @Test
+    public void typeSafeCreation() {
+        new A();
+        new C();
+        new D<>();
+    }
+
+    @Test(expected = RuntimeException.class)
+    public void typeUnsafeCreation() {
+        new B();
+    }
+
+    private static class A extends Overlay<A> {
+    }
+
+    private static class B extends Overlay<A> {
+    }
+
+    private static class C extends TabbedOverlay<C> {
+    }
+
+    private static class D<T> extends Overlay<D<T>> {
+    }
+}