Merge branch 'master' into branch-add-diagram

docs/DeveloperGuide.md

@@ -224,6 +224,24 @@ Note: While the diagram shows the lifeline of objects even after their deletion,
 
 ---
 
+### Add Grade implementation
+
+**Logic**: 
+1. `AddGradeCommand.java`
+2. `AddGradeCommandParser.java`
+
+The `addGrade` command is used by KonTActs to add an assignment and grade to a contact.
+The added assignments and grades uses `HashMap` to store the assignments and grades in each person object.
+
+This is illustrated in the activity diagram below:
+
+<puml src="diagrams/AddGradeImpl.puml" width="450" />
+
+* addGrade checks whether the assignment exists in the database, if the score is valid and if the person exists in the contacts.
+* If the conditions are satisfied, the assignment is added to the `HashMap` in the person object which stores all the added assignments of that person.
+
+---
+
 ### MarkCommand
 
 <puml src="diagrams/MarkCommandActivityDiagram.puml" width="750" />

docs/diagrams/AddGradeImpl.puml

@@ -0,0 +1,10 @@
+@startuml
+start
+:User executes addGrade command with assignment name, score and name of person;
+if () then ([AssignmentExists and ScoreValid and PersonExists])
+    :Specified assignment and score is added to specified person;
+else ([else])
+:addGrade command returns an error to the user;
+endif
+stop
+@enduml