Refactored some code.

Fixed possible issue of NullPointerException during DnD.

src/main/java/com/weis/darklaf/components/tabframe/JTabFrame.java

@@ -897,7 +897,6 @@ public class JTabFrame extends JComponent {
     public static class TabFramePosition {
         private Alignment a;
         private int index;
-        private Point point;
 
         @Contract(pure = true)
         public TabFramePosition(final Alignment a, final int index) {
@@ -905,29 +904,24 @@ public class JTabFrame extends JComponent {
             this.index = index;
         }
 
-        @Contract(pure = true)
-        public TabFramePosition(final Alignment a, final int index, final Point p) {
-            this.a = a;
-            this.index = index;
-            this.point = p;
-        }
-
+        /**
+         * Set the alignment.
+         *
+         * @param a the alignment.
+         */
         public void setAlignment(final Alignment a) {
             this.a = a;
         }
 
+        /**
+         * Set the index.
+         *
+         * @param index the index.
+         */
         public void setIndex(final int index) {
             this.index = index;
         }
 
-        public Point getPoint() {
-            return point;
-        }
-
-        public void setPoint(final Point point) {
-            this.point = point;
-        }
-
         /**
          * The alignment position.
          * This specifies at what location the tab is placed.

src/main/java/com/weis/darklaf/ui/tabbedpane/TabbedPaneTransferHandler.java

@@ -333,6 +333,7 @@ public class TabbedPaneTransferHandler extends TransferHandler implements DropTa
 
         @Override
         public DataFlavor[] getTransferDataFlavors() {
+            if (tabFlavor == null) return new DataFlavor[0];
             return new DataFlavor[]{tabFlavor};
         }
 

src/main/java/com/weis/darklaf/ui/tabframe/DarkTabFrameUI.java

@@ -32,6 +32,7 @@ import com.weis.darklaf.components.tabframe.TabFrameTab;
 import com.weis.darklaf.components.tabframe.TabFrameUI;
 import com.weis.darklaf.components.uiresource.JPanelUIResource;
 import com.weis.darklaf.util.DarkUIUtil;
+import com.weis.darklaf.util.Pair;
 import org.jdesktop.jxlayer.JXLayer;
 import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
@@ -230,6 +231,11 @@ public class DarkTabFrameUI extends TabFrameUI implements AWTEventListener {
 
     @Override
     public JTabFrame.TabFramePosition getTabIndexAt(final JTabFrame tabFrame, @NotNull final Point p) {
+        return getTabIndexAtImpl(tabFrame, p).getFirst();
+    }
+
+    protected Pair<JTabFrame.TabFramePosition, Point> getTabIndexAtImpl(final JTabFrame tabFrame,
+                                                                        @NotNull final Point p) {
         Component tabComp = null;
         Alignment a = null;
         Point pos = null;
@@ -287,33 +293,39 @@ public class DarkTabFrameUI extends TabFrameUI implements AWTEventListener {
         if (tabComp == null) {
             var tab = maybeRestoreTabContainer(tabFrame, p);
             if (tab.getAlignment() != null) {
-                return tab;
+                return new Pair<>(tab, pos);
             }
         } else {
             layout.setDraggedOver(false);
         }
         if (tabComp == null) {
-            return new JTabFrame.TabFramePosition(null, -1);
+            return new Pair<>(new JTabFrame.TabFramePosition(null, -1), pos);
         }
         var tabs = tabFrame.tabsForAlignment(a);
         for (var tab : tabs) {
             var rect = getTabRect(tab, a, tabComp, true);
             if (rect.contains(pos)) {
-                return new JTabFrame.TabFramePosition(a, tab.getIndex(), pos);
+                return new Pair<>(new JTabFrame.TabFramePosition(a, tab.getIndex()), pos);
             }
         }
-        return new JTabFrame.TabFramePosition(a, -1, pos);
+        return new Pair<>(new JTabFrame.TabFramePosition(a, -1), pos);
     }
 
     @Override
     public JTabFrame.TabFramePosition getNearestTabIndexAt(final JTabFrame tabFrame, final Point pos) {
-        var tab = getTabIndexAt(tabFrame, pos);
+        return getNearestTabIndexAtImpl(tabFrame, pos).getFirst();
+    }
+
+    protected Pair<JTabFrame.TabFramePosition, Point> getNearestTabIndexAtImpl(final JTabFrame tabFrame,
+                                                                               final Point pos) {
+        var res = getTabIndexAtImpl(tabFrame, pos);
+        var tab = res.getFirst();
         if (tab.getAlignment() != null && tab.getIndex() == -1) {
-            var p = tab.getPoint();
+            var p = res.getSecond();
             var a = tab.getAlignment();
             if (tabFrame.getTabCountAt(a) == 0) {
                 tab.setIndex(-1);
-                return tab;
+                return res;
             }
             int w = a == destAlign && destIndex == -1 ? dropSize.width : 0;
             var comp = getTabContainer(a);
@@ -344,7 +356,7 @@ public class DarkTabFrameUI extends TabFrameUI implements AWTEventListener {
                     break;
             }
         }
-        return tab;
+        return res;
     }
 
     public void setDropSize(final int width, final int height) {
@@ -388,13 +400,15 @@ public class DarkTabFrameUI extends TabFrameUI implements AWTEventListener {
     }
 
     public JTabFrame.TabFramePosition getDropPosition(final JTabFrame tabFrame, final Point p) {
-        var tab = getNearestTabIndexAt(tabFrame, p);
+        var res = getNearestTabIndexAtImpl(tabFrame, p);
+        var tab = res.getFirst();
         if (tab.getAlignment() != null) {
             var a = tab.getAlignment();
             int index = tab.getIndex();
             if (index >= 0) {
-                var rect = getTabRect(tabFrame.getTabComponentAt(a, index), a, tabFrame.getTabContainer(a), false);
-                var pos = tab.getPoint();
+                var rect = getTabRect(tabFrame.getTabComponentAt(a, index), a,
+                                      tabFrame.getTabContainer(a), false);
+                var pos = res.getSecond();
                 if (isForward(a)) {
                     if (pos.x <= rect.x + rect.width / 2 && pos.x >= rect.x) {
                         tab.setIndex(tab.getIndex() - 1);

src/main/java/com/weis/darklaf/ui/tabframe/TabFrameTransferHandler.java

@@ -61,7 +61,7 @@ import java.awt.event.MouseEvent;
 public class TabFrameTransferHandler extends TransferHandler implements DropTargetListener, SwingConstants {
 
     private static final String MIME_TYPE = DataFlavor.javaJVMLocalObjectMimeType
-            + ";class=com.weis.darklaf.components.tabframe.TabFrame";
+            + ";class=com.weis.darklaf.components.tabframe.JTabFrame";
     private static TabbedPaneDragGestureRecognizer recognizer = null;
     private final Timer timer;
     private final Timer startTimer;
@@ -381,6 +381,7 @@ public class TabFrameTransferHandler extends TransferHandler implements DropTarg
 
         @Override
         public DataFlavor[] getTransferDataFlavors() {
+            if (tabFlavor == null) return new DataFlavor[0];
             return new DataFlavor[]{tabFlavor};
         }
 

src/main/java/com/weis/darklaf/util/Pair.java

@@ -0,0 +1,46 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2019 Jannis Weis
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package com.weis.darklaf.util;
+
+import org.jetbrains.annotations.Contract;
+
+public class Pair<T, H> {
+
+    private T first;
+    private H second;
+
+    @Contract(pure = true)
+    public Pair(final T first, final H second) {
+        this.first = first;
+        this.second = second;
+    }
+
+    public H getSecond() {
+        return second;
+    }
+
+    public T getFirst() {
+        return first;
+    }
+}