[T5A2][T16-A3] DION NG

src/seedu/addressbook/commands/AddCommand.java

@@ -67,4 +67,9 @@ public CommandResult execute() {
         }
     }
 
+	@Override
+	public boolean isMutating() {
+		return true;
+	}
+
 }

src/seedu/addressbook/commands/ClearCommand.java

@@ -16,4 +16,9 @@ public CommandResult execute() {
         addressBook.clear();
         return new CommandResult(MESSAGE_SUCCESS);
     }
+
+	@Override
+	public boolean isMutating() {
+		return true;
+	}
 }

src/seedu/addressbook/commands/Command.java

@@ -38,8 +38,9 @@ public static String getMessageForPersonListShownSummary(List<? extends ReadOnly
 
     /**
      * Executes the command and returns the result.
+     * @throws Exception 
      */
-    public abstract CommandResult execute();
+    public abstract CommandResult execute() throws Exception;
 
     /**
      * Supplies the data the command will operate on.
@@ -65,4 +66,11 @@ public int getTargetIndex() {
     public void setTargetIndex(int targetIndex) {
         this.targetIndex = targetIndex;
     }
+    /**
+     * abstract class to be inherited and implemented in child 
+     * classes to check for mutating commands
+     * @return true or false 
+     */
+
+    public abstract boolean isMutating();
 }

src/seedu/addressbook/commands/DeleteCommand.java

@@ -39,4 +39,10 @@ public CommandResult execute() {
         }
     }
 
+
+	@Override
+	public boolean isMutating() {
+		return true;
+	}
+
 }

src/seedu/addressbook/commands/ExitCommand.java

@@ -16,4 +16,9 @@ public CommandResult execute() {
         return new CommandResult(MESSAGE_EXIT_ACKNOWEDGEMENT);
     }
 
+	@Override
+	public boolean isMutating() {
+		return false;
+	}
+
 }

src/seedu/addressbook/commands/FindCommand.java

@@ -53,4 +53,9 @@ private List<ReadOnlyPerson> getPersonsWithNameContainingAnyKeyword(Set<String>
         return matchedPersons;
     }
 
+	@Override
+	public boolean isMutating() {
+		return false;
+	}
+
 }

src/seedu/addressbook/commands/HelpCommand.java

@@ -25,4 +25,9 @@ public class HelpCommand extends Command {
     public CommandResult execute() {
         return new CommandResult(MESSAGE_ALL_USAGES);
     }
+
+	@Override
+	public boolean isMutating() {
+		return false;
+	}
 }

src/seedu/addressbook/commands/IncorrectCommand.java

@@ -17,4 +17,9 @@ public CommandResult execute() {
         return new CommandResult(feedbackToUser);
     }
 
+	@Override
+	public boolean isMutating() {
+		return false;
+	}
+
 }

src/seedu/addressbook/commands/ListCommand.java

@@ -22,4 +22,10 @@ public CommandResult execute() {
         List<ReadOnlyPerson> allPersons = addressBook.getAllPersons().immutableListView();
         return new CommandResult(getMessageForPersonListShownSummary(allPersons), allPersons);
     }
+
+
+	@Override
+	public boolean isMutating() {
+		return false;
+	}
 }

src/seedu/addressbook/commands/ViewAllCommand.java

@@ -37,4 +37,10 @@ public CommandResult execute() {
             return new CommandResult(Messages.MESSAGE_INVALID_PERSON_DISPLAYED_INDEX);
         }
     }
+
+
+	@Override
+	public boolean isMutating() {
+		return false;
+	}
 }

src/seedu/addressbook/commands/ViewCommand.java

@@ -38,4 +38,10 @@ public CommandResult execute() {
         }
     }
 
+
+	@Override
+	public boolean isMutating() {
+		return false;
+	}
+
 }