Add StartTime class

src/main/java/seedu/waddle/model/item/StartTime.java

@@ -0,0 +1,52 @@
+package seedu.waddle.model.item;
+
+import static java.util.Objects.requireNonNull;
+import static seedu.waddle.commons.util.AppUtil.checkArgument;
+
+import java.time.LocalTime;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+
+/**
+ * Represents the start time of the item.
+ */
+public class StartTime {
+    public static final String MESSAGE_CONSTRAINTS =
+            "Cost should be written as HHmm in 24H format. For example, 3:25pm is 1525.";
+    private static final String timePattern = "HHmm";
+    private static final DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern(timePattern);
+    private final LocalTime startTime;
+
+    /**
+     * Constructs a {@code StartTime}.
+     *
+     * @param startTime A valid start time.
+     */
+    public StartTime(String startTime) {
+        requireNonNull(startTime);
+        checkArgument(isValidCost(startTime), MESSAGE_CONSTRAINTS);
+        this.startTime = LocalTime.parse(startTime, timeFormatter);
+    }
+
+    /**
+     * Returns true if a given string is a valid Cost
+     */
+    public static boolean isValidCost(String test) {
+        LocalTime time;
+        try {
+            time = LocalTime.parse(test, timeFormatter);
+        } catch (DateTimeParseException e) {
+            return false;
+        }
+        return true;
+    }
+
+    public LocalTime getStartTime() {
+        return this.startTime;
+    }
+
+    @Override
+    public String toString() {
+        return this.startTime.toString();
+    }
+}