Improved the message when choosing between the regular java compiler …

…and the ECJ compiler, which requires Java 11+

robocode.ui.editor/src/main/java/net/sf/robocode/ui/editor/RobocodeCompilerFactory.java

@@ -12,15 +12,17 @@
 import net.sf.robocode.io.FileUtil;
 import net.sf.robocode.io.Logger;
 import net.sf.robocode.manager.IVersionManagerBase;
-import static net.sf.robocode.io.Logger.logError;
-import static net.sf.robocode.io.Logger.logMessage;
 import net.sf.robocode.ui.dialog.ConsoleDialog;
 import net.sf.robocode.ui.dialog.WindowUtil;
+import net.sf.robocode.util.JavaVersion;
 
 import javax.swing.*;
 import java.io.*;
 import java.util.Objects;
 
+import static net.sf.robocode.io.Logger.logError;
+import static net.sf.robocode.io.Logger.logMessage;
+
 
 /**
  * @author Mathew A. Nelson (original)
@@ -101,8 +103,10 @@ public boolean configureCompiler(RobocodeEditor editor) {
 
 		if (javacOK) {
 			int rc = JOptionPane.showConfirmDialog(editor,
-					"Robocode has found a working javac (Java Compiler) on this system.\nWould you like to use it?\n"
-					+ "(If you click No, Robocode will use the build-in Eclipse Compiler for Java (ECJ))",
+					"Robocode has found a working javac (Java Compiler) on this system.\nWould you like to use it?\n" +
+							"\n" +
+							"If you click No, Robocode will use the build-in Eclipse Compiler for Java (ECJ),\n" +
+							"which requires Java 11 or newer.",
 					"Confirm javac",
 					JOptionPane.YES_NO_OPTION,
 					JOptionPane.QUESTION_MESSAGE);
@@ -111,6 +115,17 @@ public boolean configureCompiler(RobocodeEditor editor) {
 				javacOK = false;
 			}
 		}
+
+		if (!javacOK) {
+			if (JavaVersion.getJavaMajorVersion() < 11) {
+				JOptionPane.showMessageDialog(editor, "Eclipse Compiler for Java (ECJ) requires\n" +
+								"Java 11 or newer to run.\n" +
+								"Please upgrade Java 11 or newer.",
+						"Error", JOptionPane.ERROR_MESSAGE);
+
+				return false; // compilerOK = false
+			}
+		}
 
 		if (!javacOK) {
 			compilerName = "Eclipse Compiler for Java (ECJ)";