Support JDK 21 and std::list

Fixes removeFirst() and removeLast() incompatibilities with methods
of the same name in the Java base class java.util.AbstractSequentialList
which were added in JDK 21 as part of JEP-431.

configure.ac has been modified to detect the version of JDK/Java for use
in testing the test-suite via the JAVA_VERSION_MAJOR variable.

Needed to continue testing removeFirst(), removeLast(), addFirst(), addLast().

Closes #3156

CHANGES.current

@@ -7,6 +7,26 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.4.0 (in progress)
 ===========================
 
+2025-04-02: wsfulton
+            [Java] #3156 Support JDK 21 and std::list. Fixes removeFirst() and removeLast()
+            incompatibilities with methods of the same name in the base class,
+            AbstractSequentialList, which were added in JDK 21 with a different
+            return type. The addFirst() and addLast() methods were also added, all part
+            of JEP-431 Sequenced Collections, see https://openjdk.org/jeps/431.
+
+            If these 4 methods are needed, as SWIG previously generated them, then add
+            the following to your interface file after %include <std_list.i>:
+
+              %extend std::list {
+                void removeLast() { $self->pop_back(); }
+                void removeFirst() { $self->pop_front(); }
+                void addLast(const T &value) { $self->push_back(value); }
+                void addFirst(const T &value) { $self->push_front(value); }
+              }
+
+            But note that this will give javac compiler errors when using JDK 21 and
+            later for removeFirst() and removeLast().
+
 2025-04-02: wsfulton
             [Java] Fix javac -Xlint warning (JDK 21):
 

Examples/test-suite/java/Makefile.in

@@ -7,6 +7,7 @@ JAVA         = @JAVA@
 JAVAC        = @JAVAC@
 JAVAFLAGS    = @JAVAFLAGS@
 JAVAC_OPTIONS = @JAVAC_OPTIONS@
+JAVA_VERSION_MAJOR = @JAVA_VERSION_MAJOR@
 JAVA_CLASSPATH_SEP = @JAVA_CLASSPATH_SEP@
 SCRIPTSUFFIX = _runme.java
 SKIP_DOXYGEN_TEST_CASES = @JAVA_SKIP_DOXYGEN_TEST_CASES@
@@ -77,6 +78,7 @@ SRCDIR       = ../$(srcdir)/
 JAVA_PACKAGE = $*
 JAVA_PACKAGEOPT = -package $(JAVA_PACKAGE)
 SWIGOPT += $(JAVA_PACKAGEOPT)
+SWIGOPT += -DJAVA_VERSION_MAJOR=$(JAVA_VERSION_MAJOR)
 
 # Ensure testsuite remains free from SWIG warnings.
 SWIGOPT += -Werror

Examples/test-suite/li_std_list.i

@@ -9,6 +9,18 @@
 #include <numeric>
 %}
 
+#if defined(SWIGJAVA) && JAVA_VERSION_MAJOR < 21
+// Test these methods which were removed in swig-4.0 as JDK added the same methods
+// in the java.util.AbstractSequentialList base but unfortunately two of them use
+// a different return type.
+%extend std::list {
+  void removeLast() { $self->pop_back(); }
+  void removeFirst() { $self->pop_front(); }
+  void addLast(const T &value) { $self->push_back(value); }
+  void addFirst(const T &value) { $self->push_front(value); }
+}
+#endif
+
 %template(BoolList) std::list<bool>;
 %template(CharList) std::list<char>;
 %template(ShortList) std::list<short>;

Lib/java/std_list.i

@@ -22,6 +22,7 @@ SWIGINTERN jint SWIG_ListSize(size_t size) {
 }
 }
 
+%javamethodmodifiers std::list::push_back "private";
 %javamethodmodifiers std::list::begin "private";
 %javamethodmodifiers std::list::insert "private";
 %javamethodmodifiers std::list::doSize "private";
@@ -54,7 +55,7 @@ namespace std {
   }
 
   public boolean add($typemap(jboxtype, T) value) {
-    addLast(value);
+    push_back(value);
     return true;
   }
 
@@ -185,14 +186,7 @@ namespace std {
     void clear();
     %rename(remove) erase;
     iterator erase(iterator pos);
-    %rename(removeLast) pop_back;
-    void pop_back();
-    %rename(removeFirst) pop_front;
-    void pop_front();
-    %rename(addLast) push_back;
     void push_back(const T &value);
-    %rename(addFirst) push_front;
-    void push_front(const T &value);
     iterator begin();
     iterator end();
     iterator insert(iterator pos, const T &value);

configure.ac

@@ -1017,31 +1017,25 @@ else
   JAVAC="$JAVACBIN"
 fi
 
-# Check Java version: we require Java 9 or later for Doxygen tests.
 if test -n "$JAVAC"; then
-    AC_MSG_CHECKING(if java version is 9 or greater)
-    javac_version=`"$JAVAC" -version 2>&1`
-    java_version_num=`echo $javac_version | sed -n 's/^javac //p'`
-    if test -z "$java_version_num"; then
-        AC_MSG_WARN([unknown format for Java version returned by "$JAVAC" ($javac_version)])
-        JAVA_SKIP_DOXYGEN_TEST_CASES=1
-        AC_MSG_RESULT(unknown)
-    else
-        dnl Until Java 8 version number was in format "1.x", starting from
-        dnl Java 9 it's just "x".
-        case $java_version_num in
-            1.*)
-                JAVA_SKIP_DOXYGEN_TEST_CASES=1
-                AC_MSG_RESULT([no, disabling Doxygen tests])
-                ;;
+  AC_MSG_CHECKING(java major version)
+  javac_version=`"$JAVAC" -version 2>&1`
+  java_version_num=`echo $javac_version | sed -n 's/^javac //p'`
+  JAVA_VERSION_MAJOR="1"
+  if test -n "$java_version_num"; then
+    dnl Until Java 8 version number was in format "1.x.y_z", starting from Java 9 it's "x.y.z".
+    JAVA_VERSION_MAJOR=[$(echo "$java_version_num" | sed -e "s/^1\.//" | sed -e "s/^\([0-9]\+\)\..*/\1/")]
+  fi
+  AC_MSG_RESULT([$JAVA_VERSION_MAJOR])
 
-            *)
-                AC_MSG_RESULT(yes)
-                ;;
-        esac
-    fi
+# Check Java version: we require Java 9 or later for Doxygen tests.
+  JAVA_SKIP_DOXYGEN_TEST_CASES=
+  if test "$JAVA_VERSION_MAJOR" -le "8"; then
+    JAVA_SKIP_DOXYGEN_TEST_CASES="1"
+  fi
 
-    AC_SUBST(JAVA_SKIP_DOXYGEN_TEST_CASES)
+  AC_SUBST(JAVA_VERSION_MAJOR)
+  AC_SUBST(JAVA_SKIP_DOXYGEN_TEST_CASES)
 fi
 
 AC_MSG_CHECKING(for java include file jni.h)