Add FindCommand implementation

src/main/java/duke/command/FindCommand.java

@@ -0,0 +1,25 @@
+package duke.command;
+
+import duke.storage.Storage;
+import duke.task.TaskList;
+import duke.ui.Ui;
+
+public class FindCommand extends Command {
+    public static final String COMMAND_WORD = "find";
+
+    private final String keyWords;
+
+    public FindCommand(String keyWords) {
+        this.keyWords = keyWords;
+    }
+
+    @Override
+    public boolean isExit() {
+        return false;
+    }
+
+    @Override
+    public void execute(TaskList tasks, Ui ui, Storage storage) {
+        ui.findTasksMessage(tasks, keyWords);
+    }
+}

src/main/java/duke/parser/Parser.java

@@ -29,6 +29,8 @@ public static Command parse(String fullCommand) throws DukeException {
                 return prepareDelete(suffix);
             case ListCommand.COMMAND_WORD:
                 return prepareList(suffix);
+            case FindCommand.COMMAND_WORD:
+                return prepareFind(suffix);
             case ExitCommand.COMMAND_WORD:
                 return new ExitCommand();
             default:
@@ -85,4 +87,12 @@ private static Command prepareList(String suffix) throws DukeException {
             return new ListCommand();
         }
     }
+
+    private static Command prepareFind(String suffix) throws DukeException {
+        if (suffix.length() == 0) {
+            throw new DukeException("You cannot search for nothing.");
+        } else {
+            return new FindCommand(suffix);
+        }
+    }
 }

src/main/java/duke/task/Task.java

@@ -35,4 +35,8 @@ public String getDescription() {
     public String toString() {
         return "[" + this.getStatusIcon() + "] " + this.getDescription();
     }
+
+    public boolean contains(String keyWords) {
+        return description.contains(keyWords);
+    }
 }

src/main/java/duke/ui/Ui.java

@@ -81,4 +81,14 @@ public void listTasksMessage(TaskList tasks) {
     public void exitMessage() {
         System.out.println("Bye. Hope to see you again soon!");
     }
+
+    public void findTasksMessage(TaskList tasks, String keyWords) {
+        System.out.println("Here are the matching tasks in your list:");
+        for (int i = 1; i <= tasks.getNumOfTasks(); i++) {
+            Task t = tasks.retrieve(i);
+            if (t.contains(keyWords)) {
+                System.out.format("%d.%s\n", i, t.toString());
+            }
+        }
+    }
 }