[T5A1][T01-T4] Li Shicheng

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

@@ -65,4 +65,9 @@ public int getTargetIndex() {
     public void setTargetIndex(int targetIndex) {
         this.targetIndex = targetIndex;
     }
+
+    /*
+     * Returns whether the given command will change the data. 
+     */
+    public abstract boolean isMutating();
 }

src/seedu/addressbook/commands/DeleteCommand.java

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

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;
+    }
+
 }

src/seedu/addressbook/logic/Logic.java

@@ -85,7 +85,8 @@ public CommandResult execute(String userCommandText) throws Exception {
     private CommandResult execute(Command command) throws Exception {
         command.setData(addressBook, lastShownList);
         CommandResult result = command.execute();
-        storage.save(addressBook);
+        if (command.isMutating())
+            storage.save(addressBook);
         return result;
     }