Sorting custom entry fields that contain numerical values

CHANGELOG.md

@@ -50,6 +50,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We fixed an issue where JabRef switched to discrete graphics under macOS [#5935](https://github.com/JabRef/jabref/issues/5935)
 - We fixed an issue where the Preferences entry preview will be unexpected modified leads to Value too long exception [#6198](https://github.com/JabRef/jabref/issues/6198)
 - We fixed an issue where custom jstyles for Open/LibreOffice would only be valid if a layout line for the entry type `default` was at the end of the layout section [#6303](https://github.com/JabRef/jabref/issues/6303)
+- We fixed an issue where sort on numeric cases was broken. [#6349](https://github.com/JabRef/jabref/issues/6349)
 
 ### Removed
 

src/main/java/org/jabref/gui/maintable/MainTableColumnFactory.java

@@ -38,6 +38,7 @@
 import org.jabref.gui.specialfields.SpecialFieldsPreferences;
 import org.jabref.gui.util.OptionalValueTableCellFactory;
 import org.jabref.gui.util.ValueTableCellFactory;
+import org.jabref.gui.util.comparator.NumericFieldComparator;
 import org.jabref.gui.util.comparator.PriorityFieldComparator;
 import org.jabref.gui.util.comparator.RankingFieldComparator;
 import org.jabref.gui.util.comparator.ReadStatusFieldComparator;
@@ -212,6 +213,7 @@ private Node createGroupColorRegion(BibEntryTableViewModel entry, List<AbstractG
         new ValueTableCellFactory<BibEntryTableViewModel, String>()
                 .withText(text -> text)
                 .install(column);
+        column.setComparator(new NumericFieldComparator());
         column.setSortable(true);
         return column;
     }

src/main/java/org/jabref/gui/util/comparator/NumericFieldComparator.java

@@ -0,0 +1,42 @@
+package org.jabref.gui.util.comparator;
+
+import java.util.Comparator;
+
+/**
+ * Comparator for numeric cases.
+ */
+public class NumericFieldComparator implements Comparator<String> {
+
+    @Override
+    public int compare(String val1, String val2) {
+        /*
+         * The purpose of this class is to add the numeric comparison, because values are sorted
+         * as if they were strings.
+         * */
+
+        // We start by implementing the comparison in the edge cases (if one of the values is null)
+        if (val1 == null && val2 == null) return 0;
+        if (val1 == null) return -1; // (we assume that "null" is "less than" any other value)
+        if (val2 == null) return 1;
+
+        // Now we start the conversion to integers.
+        Integer valInt1 = null;
+        Integer valInt2 = null;
+        try {
+            valInt1 = Integer.parseInt(val1.trim()); // In case the user added an unnecessary white space (e.g. 1 1 instead of 11)
+        } catch(NumberFormatException ignore) {} // do nothing
+        try {
+            valInt2 = Integer.parseInt(val2.trim());
+        } catch(NumberFormatException ignore) {}
+        if (valInt1 == null && valInt2 == null) return val1.compareTo(val2); // None of the values were parsed (i.e both are not numeric)
+        // so we will use the normal string comparison.
+        if (valInt1 == null) return -1; // We assume that strings "are less" than integers
+        if (valInt2 == null) return 1;
+
+        // If we arrive at this stage then both values are actually numeric !
+        return valInt1-valInt2;
+    }
+
+
+
+}