Used Polymorphism by adding isMutating() in Command Class

src/seedu/addressbook/commands/Command.java

@@ -70,4 +70,6 @@ public int getTargetIndex() {
     public void setTargetIndex(int targetIndex) {
         this.targetIndex = targetIndex;
     }
+
+    public boolean isMutating() { return true; }
 }

src/seedu/addressbook/commands/FindCommand.java

@@ -53,4 +53,6 @@ private List<ReadOnlyPerson> getPersonsWithNameContainingAnyKeyword(Set<String>
         return matchedPersons;
     }
 
+    @Override
+    public boolean isMutating() { return false; }
 }

src/seedu/addressbook/commands/HelpCommand.java

@@ -25,4 +25,8 @@ 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 +17,7 @@ public CommandResult execute() {
         return new CommandResult(feedbackToUser);
     }
 
+    @Override
+    public boolean isMutating() { return false; }
+
 }

src/seedu/addressbook/commands/ListCommand.java

@@ -22,4 +22,7 @@ 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 +37,7 @@ 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 +38,7 @@ public CommandResult execute() {
         }
     }
 
+    @Override
+    public boolean isMutating() { return false; }
+
 }

src/seedu/addressbook/logic/Logic.java

@@ -76,7 +76,7 @@ public CommandResult execute(String userCommandText) throws Exception {
     }
 
     /**
-     * Executes the command, updates storage, and returns the result.
+     * Executes the command, updates storage if data is mutated, and returns the result.
      *
      * @param command user command
      * @return result of the command
@@ -85,7 +85,9 @@ 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() == true) {
+            storage.save(addressBook);
+        }
         return result;
     }