diff --git a/concore_cli/commands/doctor.py b/concore_cli/commands/doctor.py
index 254edfd..0204583 100644
--- a/concore_cli/commands/doctor.py
+++ b/concore_cli/commands/doctor.py
@@ -35,6 +35,19 @@
             "Windows": "winget install -e --id Python.Python.3.11",
         },
     },
+    "Java (javac)": {
+        "names": {
+            "posix": ["javac"],
+            "windows": ["javac"],
+        },
+        "version_flag": "-version",
+        "config_keys": ["JAVACEXE", "JAVACWIN"],
+        "install_hints": {
+            "Linux": "sudo apt install default-jdk",
+            "Darwin": "brew install openjdk",
+            "Windows": "winget install -e --id EclipseAdoptium.Temurin.17.JDK",
+        },
+    },
     "Verilog (iverilog)": {
         "names": {
             "posix": ["iverilog"],
@@ -277,8 +290,13 @@ def doctor_check(console):
         else:
             hint = tool_def["install_hints"].get(plat_name, "")
             hint_str = f" (install: {hint})" if hint else ""
-            # Docker, MATLAB, Verilog are optional - show as warning
-            if tool_label in ("MATLAB", "Verilog (iverilog)", "Docker"):
+            # Optional tools - show as warning
+            if tool_label in (
+                "MATLAB",
+                "Verilog (iverilog)",
+                "Docker",
+                "Java (javac)",
+            ):
                 console.print(
                     f"  [yellow]![/yellow] {tool_label} -> Not found{hint_str}"
                 )
diff --git a/tests/test_doctor.py b/tests/test_doctor.py
index e9ec584..0c2d950 100644
--- a/tests/test_doctor.py
+++ b/tests/test_doctor.py
@@ -6,9 +6,11 @@
 from click.testing import CliRunner
 from concore_cli.cli import cli
 from concore_cli.commands.doctor import (
+    TOOL_DEFINITIONS,
+    _check_package,
     _detect_tool,
     _get_platform_key,
-    _check_package,
+    _get_version,
     _resolve_concore_path,
     doctor_check,
 )
@@ -209,5 +211,48 @@ def test_doctor_with_concore_sudo(self, mock_path):
         self.assertIsInstance(result, bool)
 
 
+class TestJavaDoctor(unittest.TestCase):
+    """Tests for Java toolchain support in concore doctor."""
+
+    def test_tool_definitions_include_java(self):
+        """TOOL_DEFINITIONS must include Java (javac)."""
+        self.assertIn("Java (javac)", TOOL_DEFINITIONS)
+
+        java_def = TOOL_DEFINITIONS["Java (javac)"]
+        self.assertEqual(java_def["version_flag"], "-version")
+        self.assertEqual(java_def["config_keys"], ["JAVACEXE", "JAVACWIN"])
+        self.assertIn("javac", java_def["names"]["posix"])
+        self.assertIn("javac", java_def["names"]["windows"])
+
+    def test_doctor_output_mentions_java(self):
+        """Doctor command output should include Java section."""
+        runner = CliRunner()
+        result = runner.invoke(cli, ["doctor"])
+        self.assertIn("Java (javac)", result.output)
+
+    @patch("shutil.which")
+    def test_detect_java_when_present(self, mock_which):
+        """Should detect javac when available."""
+        mock_which.side_effect = lambda cmd: (
+            "/usr/bin/javac" if cmd == "javac" else None
+        )
+        path, name = _detect_tool(TOOL_DEFINITIONS["Java (javac)"]["names"]["posix"])
+        self.assertEqual(path, "/usr/bin/javac")
+        self.assertEqual(name, "javac")
+
+    @patch("subprocess.run")
+    def test_get_version_javac_stderr_fallback(self, mock_run):
+        """javac -version outputs to stderr on older JDKs; ensure fallback works."""
+        from unittest.mock import MagicMock
+
+        mock_res = MagicMock()
+        mock_res.stdout = ""
+        mock_res.stderr = "javac 1.8.0_292\n"
+        mock_run.return_value = mock_res
+
+        ver = _get_version("/usr/bin/javac", "-version")
+        self.assertEqual(ver, "javac 1.8.0_292")
+
+
 if __name__ == "__main__":
     unittest.main()