Update JSON_STRING rutine is_equal

Update JSON_OBJECT new features (has_keys, item,get_keys), and fixed an incorrect use of HASH_TABLE

json/json_object.e

@@ -38,6 +38,8 @@ feature -- Change Element
 
 	put(key:JSON_STRING; value:JSON_VALUE) is
 			--
+			require
+				not_null: key /= Void
 			local
 				l_json_null:JSON_NULL
 				l_value:JSON_VALUE
@@ -47,9 +49,30 @@ feature -- Change Element
 					create l_json_null
 					l_value:=l_json_null
 				end
-				object.extend(key, l_value)
+				object.extend(l_value,key)
 			end
 
+feature -- Access
+	has_key(key:JSON_STRING):BOOLEAN is
+		-- has the JSON_OBJECT contains a specific key 'key'.
+		do
+			Result := object.has (key)
+		end
+
+	item(key:JSON_STRING):JSON_VALUE is
+		-- the json_value associated with a key.
+		do
+			Result:= object.item (key)
+		end
+
+	get_keys:ARRAY[JSON_STRING] is
+			--
+		do
+			Result:=object.current_keys
+		end
+
+
+
 
 feature -- Report
 	to_json:STRING is
@@ -95,6 +118,6 @@ feature -- Report
 		end
 
 
-feature -- Implementation
-	object:HASH_TABLE[JSON_STRING,JSON_VALUE]
+feature {NONE} -- Implementation
+	object:HASH_TABLE[JSON_VALUE,JSON_STRING]
 end

json/json_string.e

@@ -14,8 +14,8 @@ class
 	JSON_STRING
 	inherit
 		JSON_VALUE
-			rename
-				is_equal as is_equal_json
+			redefine
+				is_equal
 			end
 
 	create
@@ -30,6 +30,13 @@ feature -- Initialization
 
 
 feature -- Access
+feature -- Comparison
+	is_equal (other: like Current): BOOLEAN is
+			-- Is JSON_STRING  made of same character sequence as `other'
+			-- (possibly with a different capacity)?
+		do
+			Result:= Current.to_json.is_equal (other.to_json)
+		end
 
 feature -- Change Element
 	append(value:STRING)is
@@ -57,7 +64,4 @@ feature -- Status report
 
 feature {NONE} -- Implementation
 	buffer:STRING
-invariant
-	invariant_clause: True -- Your invariant here
-
 end