Added public IMainParameter interface to fix #559 (#583)

Added public IMainParameter interface to fix #559

src/main/java/com/beust/jcommander/IMainParameter.java

@@ -0,0 +1,25 @@
+/**
+ * Copyright (C) 2024 the original author or authors.
+ * See the notice.md file distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.beust.jcommander;
+
+public interface IMainParameter {
+
+	ParameterDescription getDescription();
+
+}

src/main/java/com/beust/jcommander/JCommander.java

@@ -64,7 +64,7 @@ public class JCommander {
      * Description of a main parameter, which can be either a list of string or a single field. Both
      * are subject to converters before being returned to the user.
      */
-    static class MainParameter {
+    static class MainParameter implements IMainParameter {
         /**
          * This field/method will contain whatever command line parameter is not an option.
          */
@@ -93,6 +93,7 @@ static class MainParameter {
 
         private boolean firstTimeMainParameter = true;
 
+        @Override
         public ParameterDescription getDescription() {
             return description;
         }
@@ -1144,7 +1145,7 @@ public Map<IKey, ParameterDescription> getDescriptions() {
         return descriptions;
     }
 
-    public MainParameter getMainParameter() {
+    public IMainParameter getMainParameter() {
         return mainParameter;
     }