Fix spurious virtual function related keywords

Remove virtual keyword from methods that are specific to this class
Add comment on method that hides a non-virtual base method and remove virtual keyword from it
Mark overrides with override

Author: NathanJPhillips

src/java_bytecode/expr2java.h

@@ -20,30 +20,27 @@ class expr2javat:public expr2ct
 {
 public:
   explicit expr2javat(const namespacet &_ns):expr2ct(_ns) { }
+
 protected:
   virtual std::string convert_with_precedence(
-    const exprt &src, unsigned &precedence);
-  virtual std::string convert_java_this(const exprt &src, unsigned precedence);
-  virtual std::string convert_java_instanceof(
-    const exprt &src,
-    unsigned precedence);
-  virtual std::string convert_java_new(const exprt &src, unsigned precedence);
-  virtual std::string convert_code_java_delete(
-    const exprt &src,
-    unsigned precedence);
-  virtual std::string convert_struct(const exprt &src, unsigned &precedence);
-  virtual std::string convert_code(const codet &src, unsigned indent);
+    const exprt &src, unsigned &precedence) override;
+  std::string convert_java_this(const exprt &src, unsigned precedence);
+  std::string convert_java_instanceof(const exprt &src, unsigned precedence);
+  std::string convert_java_new(const exprt &src, unsigned precedence);
+  std::string convert_code_java_delete(const exprt &src, unsigned precedence);
+  virtual std::string convert_struct(
+    const exprt &src, unsigned &precedence) override;
+  virtual std::string convert_code(const codet &src, unsigned indent) override;
   virtual std::string convert_constant(
-    const constant_exprt &src,
-    unsigned &precedence);
-  virtual std::string convert_code_function_call(
-    const code_function_callt &src,
-    unsigned indent);
+    const constant_exprt &src, unsigned &precedence) override;
+  // Hides base class version
+  std::string convert_code_function_call(
+    const code_function_callt &src, unsigned indent);
 
   virtual std::string convert_rec(
     const typet &src,
     const c_qualifierst &qualifiers,
-    const std::string &declarator);
+    const std::string &declarator) override;
 
   // length of string representation of Java Char
   // representation is '\u0000'