Converter tests:

Change test data files extension to "java"

j2k/tests/testData/ast/issues/kt-836.java

@@ -0,0 +1,31 @@
+//file
+package com.voltvoodoo.saplo4j.model;
+
+import java.io.Serializable;
+
+public class Language implements Serializable {
+        protected String code;
+
+        public Language(String code) {
+                this.code = code;
+        }
+
+        public String toString() {
+                return this.code;
+        }
+}
+
+
+class Base {
+  void test() {}
+  String toString() {
+    return "BASE";
+  }
+}
+
+class Child extends Base {
+  void test() {}
+  String toString() {
+      return "Child";
+  }
+}