--- a/src/java.desktop/share/classes/javax/swing/text/PlainView.java	Mon Nov 13 15:04:18 2017 -0800
+++ b/src/java.desktop/share/classes/javax/swing/text/PlainView.java	Tue Nov 14 10:32:31 2017 +0530
@@ -646,7 +646,7 @@
         if (tabSize == 0) {
             return x;
         }
-        float ntabs = (x - tabBase) / tabSize;
+        int ntabs = (int) ((x - tabBase) / tabSize);
         return tabBase + ((ntabs + 1) * tabSize);
     }
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/javax/swing/JTextArea/TestTabSize.java	Tue Nov 14 10:32:31 2017 +0530
@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code 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 General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+/*
+ * @test
+ * @bug 8187957
+ * @summary  Verifies Tab Size works correctly in JTextArea
+ * @run main TestTabSize
+ */
+
+import java.awt.geom.Rectangle2D;
+import javax.swing.GroupLayout;
+import javax.swing.JFrame;
+import javax.swing.JScrollPane;
+import javax.swing.JTextArea;
+import javax.swing.SwingUtilities;
+import javax.swing.text.BadLocationException;
+import javax.swing.text.Caret;
+
+public class TestTabSize {
+    private static JScrollPane jScrollPane1;
+    private static JTextArea jTextArea1;
+    private static JFrame f;
+    private static Rectangle2D rect;
+    private static Rectangle2D rect1;
+    private static boolean excpnthrown = false;
+
+    public static void main(String args[]) throws Exception {
+
+        SwingUtilities.invokeAndWait(() -> {
+            try {
+                jScrollPane1 = new javax.swing.JScrollPane();
+                jTextArea1 = new javax.swing.JTextArea();
+                jTextArea1.setTabSize(8);
+                f = new JFrame();
+
+                jTextArea1.setFont(new java.awt.Font("Monospaced", 0, 10));
+                String str =
+                        "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!#\n"
+                        + "! Some Text\t\t\t\t\t#";
+                jTextArea1.setText(str);
+                jScrollPane1.setViewportView(jTextArea1);
+
+                GroupLayout layout = new javax.swing.GroupLayout(f.getContentPane());
+                f.getContentPane().setLayout(layout);
+                layout.setHorizontalGroup(
+                    layout.createParallelGroup(
+                            javax.swing.GroupLayout.Alignment.LEADING)
+                            .addGroup(layout.createSequentialGroup()
+                                    .addContainerGap()
+                                    .addComponent(jScrollPane1,
+                                            javax.swing.GroupLayout.DEFAULT_SIZE,
+                                            446, Short.MAX_VALUE)
+                                    .addContainerGap())
+                );
+                layout.setVerticalGroup(
+                        layout.createParallelGroup(
+                                javax.swing.GroupLayout.Alignment.LEADING)
+                                .addGroup(layout.createSequentialGroup()
+                                        .addContainerGap()
+                                        .addComponent(jScrollPane1)
+                                        .addContainerGap())
+                );
+
+                f.pack();
+                int first = str.indexOf("#");
+                jTextArea1.setCaretPosition(first);
+                Caret caret = jTextArea1.getCaret();
+                rect = jTextArea1.modelToView2D(caret.getDot());
+                System.out.println("caret x position " + rect.getX());
+
+                jTextArea1.setCaretPosition(str.indexOf("#", first+1));
+                caret = jTextArea1.getCaret();
+                rect1 = jTextArea1.modelToView2D(caret.getDot());
+                System.out.println("2nd caret x position " + rect1.getX());
+
+            } catch (BadLocationException ex) {
+                excpnthrown = true;
+            } finally {
+                f.dispose();
+            }
+        });
+        if (excpnthrown) {
+            throw new RuntimeException("BadLocationException thrown");
+        }
+        if ((int)rect.getX() != (int)rect1.getX()) {
+            throw new RuntimeException("Tab width calculation wrong");
+        }
+    }
+}