From 567488b59e786e0e258cb00584fbb11afea23649 Mon Sep 17 00:00:00 2001
From: Mark Taylor <m.b.taylor@bristol.ac.uk>
Date: Thu, 5 Mar 2026 10:58:53 +0000
Subject: [PATCH] table: refine JTable overlong cell ellipsis positioning

Modify the recent change that elides overlong strings displayed
in JTable cells in the middle; the ellipsis may now be placed
either in the middle or at the end, depending on content.

Roughly, strings with embedded whitespace (which are likely to
be natural language text or similar) are elided at the end,
but long strings without embedded whitespace (which are more likely
to be something hierarchical like a filename or URL) are elided
in the middle.
---
 .../ac/starlink/table/gui/CustomLabelUI.java  | 26 +++++++++++++++++--
 topcat/src/docs/sun253.xml                    |  4 +--
 ttools/src/docs/sun256.xml                    |  4 +--
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/table/src/main/uk/ac/starlink/table/gui/CustomLabelUI.java b/table/src/main/uk/ac/starlink/table/gui/CustomLabelUI.java
index e7f69eeb2..3d926cae3 100644
--- a/table/src/main/uk/ac/starlink/table/gui/CustomLabelUI.java
+++ b/table/src/main/uk/ac/starlink/table/gui/CustomLabelUI.java
@@ -2,6 +2,7 @@
 
 import java.awt.FontMetrics;
 import java.awt.Rectangle;
+import java.util.regex.Pattern;
 import javax.swing.Icon;
 import javax.swing.JComponent;
 import javax.swing.JLabel;
@@ -23,6 +24,8 @@
 public class CustomLabelUI extends BasicLabelUI {
     private static final String ELLIPSES = "...";
     private static final int ELLIPSES_LEN = ELLIPSES.length();
+    private static final Pattern EMBEDDED_WHITESPACE =
+        Pattern.compile( "[^\\s]\\s+[^\\s]" );
     private String displayedText_;
 
     /**
@@ -71,12 +74,12 @@ protected String layoutCL( JLabel label, FontMetrics fontMetrics,
             return displayedText_;
         }
 
-
         /* Check if a truncation occurred, and if the text is long enough. If
          * the text is too short, there is no point in truncating differently.*/
         int displayedLength = displayedText_.length();
         if ( !displayedText_.equals( text ) &&
-             displayedLength > 2 * ELLIPSES_LEN ) {
+             displayedLength > 2 * ELLIPSES_LEN &&
+             isCentralElisionPreferred( text ) ) {
             int splitLength =
                 ( displayedLength + ELLIPSES_LEN ) / 2 - ELLIPSES_LEN;
             String beforeEllipses = displayedText_.substring( 0, splitLength );
@@ -94,4 +97,23 @@ protected String layoutCL( JLabel label, FontMetrics fontMetrics,
 
         return displayedText_;
     }
+
+    /**
+     * Indicates whether text should be truncated by eliding text in the
+     * middle, rather than at the end.
+     *
+     * @param  txt  text to test
+     * @return   true if central elision is preferred
+     */
+    private boolean isCentralElisionPreferred( String txt ) {
+        if ( txt == null ||
+             txt.length() == 0 ||
+             txt.endsWith( ELLIPSES ) ||
+             EMBEDDED_WHITESPACE.matcher( txt ).find() ) {
+            return false;
+        }
+        else {
+            return true;
+        }
+    }
 }
diff --git a/topcat/src/docs/sun253.xml b/topcat/src/docs/sun253.xml
index 014f6db6a..ebe7b1505 100644
--- a/topcat/src/docs/sun253.xml
+++ b/topcat/src/docs/sun253.xml
@@ -34926,8 +34926,8 @@ introduced since the last version:
         <ref id="form-histogram">histogram</ref> plots.</li>
     <li>Overlong text and array fields in the
         <ref id="TableViewerWindow">Data Window</ref>
-        are now displayed with an ellipsis (...) in the middle
-        rather than at the end.</li>
+        are now in some cases displayed with an ellipsis (...)
+        in the middle rather than at the end.</li>
     <li>Functions 
         <ref id="Coverage-uniqToOrder"><code>uniqToOrder</code></ref> and
         <ref id="Coverage-uniqToIndex"><code>uniqToIndex</code></ref>
diff --git a/ttools/src/docs/sun256.xml b/ttools/src/docs/sun256.xml
index 2c19f53cc..ad75be319 100644
--- a/ttools/src/docs/sun256.xml
+++ b/ttools/src/docs/sun256.xml
@@ -16035,8 +16035,8 @@ eds. C. Gabriel et al., ASP Conf. Ser. 351, p. 666 (2006)
         <ref id="layer-histogram">histogram</ref> plots.</li>
     <li>Overlong text and array fields in the
         <ref id="mode-gui"><code>gui</code></ref> output mode table
-        window are now displayed with an ellipsis (...) in the middle
-        rather than at the end.</li>
+        window are now in some cases displayed with an ellipsis (...)
+        in the middle rather than at the end.</li>
     <li>Functions
         <ref id="Coverage-uniqToOrder"><code>uniqToOrder</code></ref> and
         <ref id="Coverage-uniqToIndex"><code>uniqToIndex</code></ref>